Many significant and clinically impactful developments have been made in the fields of intraocular lenses (IOLs) and cataract surgical techniques in the academic years 2012–2013. Introduction and more widespread application of femtosecond (FS) laser technology in cataract surgery promise to enhance precision and safety and to improve technical surgical outcomes. However, whether the cost-benefit ratio will allow its widespread acceptance still remains to be seen. At the other extreme, there are still situations, particularly in the developing world, where manual small-incision cataract surgery (M-SICS) is practiced. This surgical technique promises to offer equivalent outcomes and is much more cost-effective than phacoemulsification.
As cataract surgery is evolving, the emphasis is on refractive outcomes, enhancement of quality of vision, and lifestyle. Intraocular lenses using advanced technologies such as toric, multifocal, and multifocal toric IOLs offer a good range of unaided visual acuity and reduced spectacle dependence.
This review incorporates only a selected number of articles involving clinical and experimental trials that appeared in literature in the English language. All the articles included in the review have been listed in PubMed between January 1, 2013, and December 31, 2013. Keywords that have been used to carry out the search are phacoemulsification, cataract surgery, toric IOLs, multifocal IOLs, multifocal toric IOLs, FS laser cataract surgery, surgically induced astigmatism (SIA), and small-incision cataract surgery (SICS).
The idea has been to include clinically relevant, novel, and pertinent articles published in peer-reviewed literature that will provide helpful insights, which can be implemented to enhance surgical and visual outcomes for cataract patients.
FEMTOSECOND LASER-ASSISTED CATARACT SURGERY
Cataract surgery is the most commonly performed ophthalmic procedure worldwide. The application of FS lasers has the potential to improve patient outcomes and allows surgeons of different experience and skill levels to perform better cataract surgeries. The effect of this new technology on refractive and visual outcomes, complication rates, patient safety, and cost-effectiveness for both patients and health insurance organizations has generated much interest and discussion among ophthalmologists.1–3
Femtosecond lasers deliver ultrashort pulses of energy at infrared wavelengths at close proximity. Technology integrating high-resolution anterior segment imaging with an FS laser is capable of treating tissue that is significantly deeper in the eye. This technology now offers a system with the capacity to create main, side-port, and astigmatic corneal incisions, anterior capsulotomy and fragmenting, and softening of the nucleus. The advantage is that it uses automated, computer-guided laser precision, and there is minimal collateral tissue damage. There has been substantial progress in surgical and visual outcomes after the introduction of first-generation FS cataract lasers. Indeed, there is an emerging body of evidence highlighting benefits such as reduced phacoemulsification time, better wound architecture, greater precision and accuracy of anterior capsulotomy, and more stable and predictable positioning of the IOL.4–10
The Value of Surgical Experience During Femtosecond Laser Cataract Surgery
Roberts et al11 evaluated the surgical outcomes and safety of FS laser cataract surgery with greater surgical experience, modified techniques, and improved technology. They prospectively evaluated 1500 consecutive eyes undergoing FS laser cataract surgery and refractive lens exchange surgery between April 2011 and March 2012. All cases underwent anterior capsulotomy, lens fragmentation, and corneal incisions using the Alcon LenSx FS laser. The patients were divided into 2 groups. Group 1 consisted of the first 200 cases, and group 2 was composed of the subsequent 1300 cases. The same surgeon performed all the surgeries. The 2 groups were compared for intraoperative complication rates.
The authors observed that anterior capsule tears (4% vs 0.31%), posterior capsule tears (3.5% vs 0.31%), and posterior lens dislocation (2% vs 0%) were significantly lower in group 2. The number of docking attempts per case (1.5 vs 1.05%), incidence of postlaser pupillary constriction (9.5% vs 1.23%), and anterior capsular tags (10.5% vs 1.61%) were also significantly lower in group 2. Therefore, in the present study, particularly noteworthy was the observation that the complication rates were higher in group 1 as compared with group 2 The differences were statistically significant for all parameters.
The variables in the study were the surgeon’s experience with FS lasers, the addition of 1 drop of 10% phenylephrine immediately after the LenSx procedure, and technical enhancement of the LenSx system. The authors concluded that the surgical outcomes and safety of FS laser cataract surgery improved significantly with greater surgical experience, development of modified techniques, and improved technology. The complication rates observed in this study were comparable to reports of complication rates observed in manual phacoemulsification surgery.
This study validates the safety and efficacy of FS laser cataract surgery. There is a definite learning curve while adopting this technology. The differences in the results between the 2 groups can be attributed both to the initial learning curve of the surgeon and improvements in the software and docking systems of the laser platform over time.
Lens Fragmentation and Anterior Capsulotomy Using Femtosecond Laser Cataract Surgery—A Review of 3 Studies
Reddy et al12 studied the safety and effectiveness of FS laser–assisted lens fragmentation and anterior capsulotomy versus the manual technique. Patients were randomized to receive either FS laser–assisted lens prefragmentation and capsulotomy (56 eyes) or manual capsulorhexis and standard phacoemulsification (63 eyes). The study was performed using the VICTUS FS laser platform (Bausch and Lomb Technolas). The authors found that effective phaco time (EPT) was lower in the femtolaser group (5.2 ± 5.7 seconds) as compared with the manual group (7.7 ± 6.0 seconds). Other authors have also reported this previously. The mean phaco energy was also significantly lower in patients who underwent FS laser–assisted pretreatment (13.8% ± 10.3% in the laser group and 20.3% ± 8.1% in the manual group).
The authors believed that with the increasing experience of the surgeon in using the FS cataract procedure and optimum use of different fragmentation patterns for different cataract grades, it was possible to further reduce EPT. The circularity and intended diameter of capsulotomy were studied ex situ. Analyzing in situ snapshots assessed the centration of capsulotomy. Laser-assisted capsulotomies were significantly more accurate and precise in terms of the intended diameter, circularity, and centration. The authors also found that the safety profile of the procedures was equivalent. However, the surgeons did not report any difference in the ease of performing phacoemulsification in either group of patients.
In another study, Abell et al13 prospectively compared EPT after FS laser pretreatment and conventional phacoemulsification. They observed the associated effects on visual outcomes and endothelial cell loss. The CATALYS Femtosecond Laser System (OptiMedica USA) was used. Two hundred one consecutive eyes that underwent FS laser–assisted cataract surgery (cases) were compared with 51 eyes (controls) that underwent conventional phacoemulsification followed by IOL insertion. One hundred percent of the cases pretreated with FS laser had complete capsulotomy. The mean EPT was reduced by 83.6% in the FS pretreatment group as compared with the controls.
During the course of the study, lens fragmentation patterns were altered to improve the ease of cataract extraction. Furthermore, the last few patients (24 cases, 3 controls) underwent phacoemulsification with a larger phacoemulsification tip (20 gauge). After optimization of the FS pretreatment group with grid size and phacoemulsification tip, the overall reduction in EPT was 96.2% when compared with controls. Also, 30% of eyes in the FS pretreatment group had 0 EPT. None of the eyes in the control group had 0 EPT. Lower phacoemulsification times were recorded consistently across the FS group. An EPT of less than 4 seconds was observed in 80.7% of cases. The lowest EPT time in the conventional group was 4.90 seconds. The lower EPT in the FS group was associated with a 36.1% reduction in endothelial cell loss. However, there was no significant difference between the groups in terms of preoperative and postoperative mean endothelial cell count.
In yet another study, Conrad-Hengerer et al14 studied the corneal endothelial cell count and corneal thickness measurements in patients undergoing standard phacoemulsification compared with FS laser–assisted cataract removal. They did a prospective, randomized, intraindividual cohort study. One eye of the patient was randomized to undergo FS laser–assisted cataract surgery (CATALYS; OptiMedica), and the other eye received conventional phacoemulsification (control group). The authors observed the corneal endothelial cell loss, corneal thickness, and EPT for 3 months. The postoperative results were as follows: mean endothelial cell loss (FS laser group: 7.9% ± 7.8% (1 week), 8.1% ± 8.1% (3 months)] and [control group: 12.1% ± 7.3% (1 week), 13.7% ± 8.4% (3 months)]; mean relative change in corneal thickness from the preoperative values [FS laser group: 0.0% ± 1.9% (1 day), 2.8% ± 1.8% (1 week), 3.3% ± 1.7% (3 months)] and [control group: 0.9% ± 2.3% (1 day), 2.4% ± 1.5% (1 week), 3.2% ± 1.4% (3 months)]. The differences in the corneal endothelial cell loss and corneal thickness were statistically significant over the entire postoperative period. The endothelial cell loss at the 3-month postoperative visit and the corrected distance visual acuity (CDVA) showed a positive correlation with EPT in the femtolaser group. So the authors concluded that FS laser–assisted cataract surgery with softening of the lens before phacoemulsification led to a significant reduction in endothelial cell loss and quicker visual recovery.
Pretreatment with the FS laser system helps in reducing EPT and mean phaco energy. This may favorably impact the health of the anterior segment and the corneal endothelium. This, in turn, may potentially lead to quicker visual recovery after cataract surgery.
Anterior Capsulotomy Integrity Using the Femtosecond Laser System
Auffarth et al15 did a pig eye laboratory study to objectively measure the strength of capsulotomy when performed with an FS-assisted technique as compared with a manual capsulotomy procedure. Ten fresh pig eyes were randomly assigned to either FS laser–assisted capsulotomy (VICTUS FS laser platform from Bausch and Lomb Technolas USA) or manual capsulotomy. After capsulotomy was performed, the authors removed the cornea, and the anterior capsule was cut out with microscissors. It was immersed in an ophthalmic viscosurgical device (OVD), and capsule retractors were positioned within this donut-shaped capsule. The left retractor was fixed, whereas the right retractor moved at a constant speed controlled by the pull force measuring device (Alluris GmbH 7 Co. KG Germany). The maximum amount of force immediately before tissue rupture was measured. The mean rupture force was 113 ± 12 mN for the laser-assisted procedure and 73 ± 22mN for the manual procedure. So the laser-assisted procedure had a significantly higher rupture force than the manual procedure. The authors also measured the mean stretching ratio of the capsule. This was defined as the diameter of the donut-shaped anterior capsule immediately before rupture divided by the unstretched diameter. The mean stretching ratios were 1.60% ± 0.10% for the laser-assisted procedure and 1.35% ± 0.04% for the manual procedure. This ratio was also significantly higher for the laser-assisted procedure. The authors observed that these results were similar to previously published results for the LenSx and LensAR FS platforms (reference15).
This study highlights that anterior capsulotomies made with the FS laser platform provide stronger capsular openings as compared with the manual technique in a laboratory setting using pig eyes. This may be advantageous in complicated cataract cases, pseudoexfoliation syndrome cases, pediatric cases, white cataracts, and other difficult situations. A stronger, more resistant capsular rim is also beneficial for cataract surgery in eyes with very dense lenses.
However, anterior capsules of pigs are known to be anatomically thicker and more elastic. Therefore, the findings of this study might not be fully comparable to those obtained from a clinical setting.
Small Pupils and Femtosecond-Assisted Cataract Surgery—A Review of 2 Studies
Femtosecond laser–assisted cataract surgery requires adequate dilation for imaging and treatment. A minimum 5.5-mm preoperative dilation is required to perform a 5-mm anterior capsulotomy using an FS laser platform.
Conrad-Hengerer et al16 evaluated the efficacy of different treatment modalities in eyes with small pupils before FS laser–assisted cataract surgery. Of the 850 eyes scheduled for cataract surgery, 40 eyes had an intraoperative pupil size smaller than 5.5 mm. A sequential 3-step treatment protocol was followed to achieve a pupil larger than 5.5 mm: (1) intracameral administration of epinephrine solution, (2) additional viscomydriasis, and (3) implantation of a Malyugin ring pupil expander.
To achieve a pupil larger than 5.5 mm, epinephrine was sufficient in 7% of the eyes (step 1). Additional viscomydriasis was necessary in 25% of the eyes (step 2), and the pupil expander was implanted in 68% of the eyes (step 3).
The FS laser platform was housed outside the operating room. When any 1 of the 3 steps enlarged the pupil to at least 5.5 mm, FS laser–assisted cataract surgery was performed with an anterior capsulotomy diameter of at least 4.5 mm and nuclear fragmentation grids of 350 μm (CATALYS; OptiMedica). This was followed by phacoemulsification and IOL implantation.
There was no difficulty in capturing an optical coherence tomography image. The posterior capsule could be identified, and anterior capsulotomy was completed in all the cases. There were tongue-like lesions of the capsulotomies detected in 5 eyes. However, tears were observed in the anterior or posterior capsules. No severe intraoperative complications occurred in any of the eyes.
In yet another study, Burkhard and Schultz17 also described certain methods for performing FS laser–assisted cataract surgery in eyes with small pupils. In 73 eyes with small pupils, laser treatment was possible after installing a mechanical dilation device. Iris retractors or a Malyugin ring was used for mechanical pupil dilation before laser capsulotomy and lens fragmentation. With and without an OVD, no flattening of the anterior chamber or other complications occurred during redocking, laser treatment, or the manual part of the procedure. Small adhesions of anterior capsulotomy were more frequent when the anterior chamber was still filled with the OVD and did not occur when the OVD was removed.
A small, poorly dilated pupil constitutes a major challenge in cataract surgery, particularly when performing capsulorhexis. Femtosecond laser–assisted cataract surgery can be considered even in a scenario in which a pupil cannot be dilated. It is safe to first go ahead with intraoperative pupillary dilation techniques, fill up the eye with an appropriate OVD, and then shift the patient to the FS laser platform. Following this technique does not seem to affect the safety and efficacy of the FS laser procedure. This protocol may also be used in surgical setups in which the FS laser platform may be housed outside the main operating room.
Bag-in-the-Lens and the Femtosecond Laser Technique—A Review of 2 Studies
Tassingnon et al18 first described the bag-in-the-lens technique in 2002. This technique is designed to prevent posterior capsular opacification, which is the most frequent complication of modern cataract surgery. It also ensures excellent IOL centration and a predictable effective lens position. Creating an appropriately sized and centered anterior and posterior capsulotomies relative to each other is important in bag-in-the-lens implantation. The posterior continuous curvilinear capsulorhexis in the bag-in-the-lens technique has been criticized as being too difficult for routine manual performance.19
Dick et al20 have described a technique for performing bag-in-the-lens IOL implantation using the FS laser–assisted technique (CATALYS; OptiMedica). Thirty-one cases of bag-in-the-lens were performed. The technique they used has been briefly described here. Initially, anterior capsulotomy, lens fragmentation, and corneal incisions were performed followed by routine phacoemulsification. The posterior capsule was then carefully opened with a 27-gauge self-bent needle. Sodium hyaluronate 1% (Healon) was injected through the opening to push back the anterior vitreous. The patient was then moved again to the FS laser platform where a second docking was performed. The posterior capsule was then observed on the optical coherence tomography performed by the system. However, its exact demarcation and safety zones needed to be confirmed manually. The laser was once again fired to perform posterior capsulorhexis. The patient was then moved back again under the operating microscope. The posterior capsulorhexis flap was carefully removed, and bag-in-the-lens was implanted.
The results of the study showed that there were no major intraoperative or postoperative complications or vitreous disturbance in any of the cases. Indeed, postoperative visual acuity improved in all eyes. There was no significant difference between preoperative and postoperative intraocular pressures at 1 week and 1 month.
The main limitation in the widespread acceptance of the bag-in-the-lens technique is that it has been considered too difficult for routine manual performance. The FS laser is capable of performing anterior and posterior capsulotomies of the desired size and centration in a reproducible way. It may even be possible to create a posterior capsulotomy with the FS laser without performing any nick in the posterior capsule intraoperatively. This may facilitate a more general usage of the bag-in-the-lens implantation technique. However, a limitation in the use of this procedure is that it requires the use of 2 separate patient docking interfaces. This will increase the cost of surgery even more than what it currently is.
DIFFERENT CATARACT SURGICAL TECHNIQUES AND TECHNOLOGIES
Manual Small-Incision Cataract Surgery
Manual SICS is a frequently used technique in eye camps and high-volume surgical settings. There are a few studies evaluating M-SICS and phacoemulsification in literature.21–26 The main cited advantages of M-SICS are its short-term cost-effectiveness, its low dependence on technology, and the short surgical duration. The disadvantages of this technique include low uncorrected visual acuity (UCVA) and high-induced astigmatism,27 which limits visual outcomes.
Manual Small-Incision Cataract Surgery in an Outreach Program—A Prospective Evaluation
Nowak and Grzybowski28 evaluated the CDVA and complication rates following M-SICS performed on 84 patients in an outreach program. A CDVA of 0.3 (probably in LogMar as not mentioned) (6/12) or better was achieved in 98.6% of cases at 6 weeks. Posterior capsule rupture occurred in 1 (1.2%) of 84 patients without vitreous loss. Minor hyphemas were observed in 12 (14.3%) of 84 eyes, which resolved without intervention.
From this study, it is evident that a high percentage of avoidable blindness can be tackled by implementing appropriate programs. High-volume cataract surgery in an eye camp setting with the application of appropriate surgical techniques and standardized protocols of disinfection and sterilization does not compromise the quality of visual outcomes after surgery.
Manual Small-Incision Cataract Surgery—An Endothelium Evaluation
Evaluation of corneal endothelial loss and edema is a measure of surgically induced endothelial damage. Density of nuclear sclerosis, intraoperative mechanical touch,29 and OVD30 contribute to the endothelial integrity.
Goldenberg et al31 prospectively evaluated the corneal endothelial cell loss and central corneal thickness in eyes that underwent a modification of M-SICS. In this approach, they used an anterior chamber maintainer throughout the surgery with addition of an ocular viscoelastic device prior to nucleus removal. The authors examined the eyes at the 1-week and 1-month follow-up visits. They found significant endothelial loss at 1 week postoperatively (P = 0.003). Central corneal thickness showed a significant increase at the 1-week and 1-month follow-up visits. However, the peripheral corneal thickness measurements at 12- and 6-o’clock hours remained unaffected.
The modified M-SICS technique used by the authors is a viable enhancement with mild and transient impact on the corneal endothelial cell density and corneal pachymetry.
Manual Small-Incision Cataract Surgery: Results of 2 Meta-analyses
Jaggernath et al32 did a systematic search of research articles to compare the safety, efficacy, and cost-effectiveness of M-SICS versus phacoemulsification. In the 42 articles that they included in their analysis, all the studies showed that both techniques were safe and effective. However, phacoemulsification was more expensive because of medication and instrumentation costs. Also the authors found that phacoemulsification involved a steep learning curve for surgeons. As far as visual acuity was concerned, the eyes that underwent phacoemulsification had better UCVA as against eyes that underwent M-SICS because of low astigmatism. The literature also points to M-SICS being more useful for intumescent and hard cataracts.
Manual SICS is comparable to phacoemulsification in almost all aspects except for postoperative astigmatism. Also because of the low-cost factor, M-SICS seems to be the preferred approach in settings with fewer resources such as eye camps.
Another meta-analysis was undertaken by Zhang et al33 to compare visual outcomes in eyes with phacoemulsification and SICS. The primary outcome measures included CDVA and uncorrected distance visual acuity (UDVA). Secondary outcomes were SIA, percentage of endothelial cell loss, and other complications. In the 6 randomized controlled trials that were analyzed, a greater proportion of patients in the phacoemulsification group had a final UCVA of 6/9 or greater, whereas a greater proportion of patients in the SICS group had a UCVA of less than 6/18. The groups were similar regarding best corrected visual acuity (BCVA), complications, and percentage of endothelial cell loss. A very remarkable difference between the groups was that phacoemulsification induced significantly less SIA.
This meta-analysis has shown that phacoemulsification is superior to SICS in CDVA and causes less SIA, but there are no significant differences in visual rehabilitation, endothelial cell loss, and complication rates between the groups.
With developments in IOL technology and increasing patient expectations, good functional vision may be considered more crucial while evaluating surgical outcomes. Riaz et al34 performed a review of 8 randomized controlled trials that compared SICS and phacoemulsification. They defined 2 primary outcomes: “good functional vision” (presenting a visual acuity of 6/12 or better) and “poor visual outcome” (BCVA of <6/60). They also collected data on posterior capsule rupture rates, other complications, and cost-effectiveness of the 2 techniques. Most studies reported a visual acuity of 6/18 or better (rather than 6/12 or better) at 6 to 8 weeks after surgery, indicating no difference between the M-SICS and phacoemulsification groups. The complications reported were low for both techniques. One study reported that cost was more than 4 times higher using phacoemulsification as compared with M-SICS.
On the basis of this review, the authors concluded that phacoemulsification may result in better BCVA on a short-term basis (up to 3 months after surgery) compared with M-SICS but similar BCVA.
In view of the low cost of M-SICS, this appears to be a viable technique in patient populations where high-volume surgeries are a priority.
Further randomized, clinical trial studies are required with a longer-term follow-up to better assess uncorrected visual outcomes as it is important for everyday ambulatory vision. Indeed, most patients prefer not to use spectacles and rely on uncorrected vision. Also, assessment of low contrast sensitivity performance may enable us to translate the information and compare visual functions in the context of the difficulty that an individual patient may face on a daily basis in recognizing a variety of visual targets. With changing trends in refractive cataract surgery, the use of customized IOLs, and the increasing demand for 100% visual outcomes from patients,35 it has become imperative for surgeons to deliver optimum visual outcomes after cataract surgery.
INTRAOCULAR LENS TECHNOLOGIES
Toric Intraocular Lenses
According to published literature, up to 22% to 26% of patients undergoing cataract surgery have 1.5 diopters (D) or more of preexisting corneal astigmatism.36–38 These patients often require management of corneal astigmatism with either spectacles, contact lenses, or additional corneal refractive procedures such as limbal relaxing incisions, laser-assisted in situ keratomileusis, or photorefractive keratectomy.
Correction of astigmatism at the time of cataract surgery is possible using incisional techniques, such as astigmatic keratotomy, or by implanting a toric IOLs. These IOLs have been widely reported to be safe and effective, and they offer predictable visual outcomes,39–41 even in cases of high astigmatism,42 keratoconus (KC),43 pellucid marginal degeneration (PMD),44 megalocornea,45 and postkeratoplasty astigmatism.46 This review includes selected articles highlighting the various aspects of toric IOLs.
The Role of the Posterior Cornea in Measuring Corneal Astigmatism—A Review of 3 Studies
Today, the current practice is to use anterior corneal astigmatism, assessed by various devices, to evaluate corneal astigmatism. Based on this evaluation, the appropriate toric IOL model is chosen.
However, Koch et al47 evaluated the impact of posterior corneal astigmatism on outcomes following toric IOL implantation. As they pointed out, several studies,48–54 including theirs,47 have suggested that posterior corneal astigmatism does contribute to total corneal astigmatism. Therefore, ignoring this aspect may lead to residual refractive errors and potentially dissatisfied patients. In their prospective study, 41 eyes of 41 patients underwent preoperative corneal astigmatism measurements using 5 different devices, 4 of which measured only anterior corneal astigmatism and 1 measured total corneal astigmatism, based on anterior and posterior corneal astigmatism. These measurements were performed preoperatively and at 3 weeks postoperatively. Postoperatively, the manifest refraction was corrected at the corneal plane. Effective toric power at the corneal plane was calculated using the Holladay 2 IOL consultant software. The difference between the manifest refraction and effective toric power gave the assumed actual corneal astigmatism.
With each of the 5 devices, that is, IOL Master, manual keratometer, LENSTAR, Atlas Topographer, and the Galilei Dual Scheimpflug system, the corneal astigmatism prediction error was calculated as the difference between actual corneal astigmatism and that measured by the particular device.
For further understanding, the eyes were subdivided into 2 categories: those having with the rule (WTR) astigmatism and those with against the rule (ATR) astigmatism, based on the orientation of the steep meridian.
On data analysis, the authors reported that in eyes with WTR astigmatism, the mean corneal astigmatism prediction error was 0.5 to 0.6 D with all devices. However, in eyes with ATR astigmatism, the mean corneal astigmatism prediction error was 0.2 to 0.3 D. The Galilei, however, did not give much corneal prediction error in ATR astigmatism eyes, although it did give an error of about 0.57 D error in WTR eyes. This suggests that even the Galilei device tends to underestimate posterior corneal astigmatism in WTR eyes.
In a previous study, the same authors have reported that the posterior cornea was steeper along the vertical axis in most eyes. They further stated that the magnitude of posterior corneal astigmatism increased as the magnitude of anterior WTR astigmatism increased. In eyes with ATR astigmatism, however, the posterior corneal astigmatism was about 0.2 D, and it did not change with changing magnitude in anterior corneal astigmatism. Now, the existence of a steeper posterior cornea along the vertical meridian would mean net plus refractive power along the horizontal meridian. This would mean that if only anterior corneal astigmatism was considered, there would be an overestimation of WTR astigmatism. In such a case, there would be the possibility that the greater the magnitude of anterior WTR astigmatism, the higher would be the underestimation. Similarly, in ATR astigmatism, there would be underestimation, which would probably be the same irrespective of the magnitude of anterior corneal astigmatism. Based on their results, the authors also suggested a new nomogram, the Baylor toric IOL nomogram for selection of toric IOL power.
There are several issues involved in the use of the Baylor toric IOL nomogram for selection of toric IOL power, which have not been addressed in this study. Chief among these are the difficulties involved in measuring the actual amount of astigmatism induced by the toric IOL, any effects of tilt/decentration of the IOL, and higher-order aberrations (HOAs), which may manifest as refractive astigmatism. Despite these limitations, the article opens up avenues for further, detailed, prospective randomized trials using different devices.
In another retrospective study, Eom et al55 USA tried to evaluate the differences in the axes of corneal and internal astigmatism. They studied 180 eyes and assessed corneal andinternal astigmatism on the Wavefront Analyzer (KR-1 W; Topcon, USA). Internal astigmatism is basically a combination of posterior corneal and lenticular astigmatism. Axis differences between corneal and internal astigmatism were further subdivided as on-axis differences (axis difference between internal and corneal astigmatism of 180 ± 10 degrees), opposite axis differences (axis difference between internal and corneal astigmatism of 90 ± 10 degrees), or oblique axis difference.
On an analysis of corneal astigmatism, the authors found that 46.1% of eyes had more than 1.0 D of astigmatism, and 22.2% of eyes had more than 1.5 D of astigmatism.
While examining internal astigmatism, 45.5% of eyes (82 eyes) had more than 1.0 D of astigmatism and 18.9% of eyes (34 eyes) had more than 1.5 D of internal astigmatism. The axis difference was on-axis in only 10.0% of eyes, whereas in the rest, it was either oblique or opposite axis. Furthermore, 10% of eyes had an opposite axis difference with more than 1.0 D of both corneal and internal astigmatism.
The study by Eom et al provides some interesting insights. When corneal astigmatism and internal astigmatism are on the same axis, the postoperative refractive astigmatism usually decreases as compared with the preoperative refractive astigmatism. On the other hand, when corneal astigmatism and internal astigmatism are on opposite axes, the internal astigmatism will have a neutralizing effect on the corneal astigmatism. This will result in greater refractive astigmatism postoperatively, with poorer unaided visual acuity, as compared with the preoperative visual acuity.
Thus, surgeons should be particularly careful in correcting corneal astigmatism when the internal astigmatism is aligned on the opposite axis. Also, an understanding of this will help in counseling the patient regarding the need for a toric IOL, even though he/she may not need astigmatic correction prior to cataract surgery.
Overall, these 3 studies highlight and emphasize the value of addressing coexisting corneal astigmatism. While toric IOLs are becoming increasingly popular, there are instances in which targeted astigmatic correction is often not achieved. Surgeons should be aware of and investigate posterior corneal contributions to astigmatism to achieve better accuracy. It appears that corneal astigmatism is overestimated in WTR by all devices and underestimated in ATR by all except the Placido-dual Scheimpflug analyzer.
Assessing internal astigmatism is also important for toric IOL decision making. Patients with significant amount of corneal and internal astigmatism on opposite axes will be more dissatisfied with visual outcomes following a nontoric IOL implantation.
Selection of Toric Intraocular Lens Power—A Review of 2 Studies
Accurate calculation of IOL power and selection of the right IOL model for implantation are crucial for success with toric IOLs. Currently, there are 10 different toric IOLs available worldwide. Most of them offer their own calculators that can be used to calculate and decide which toric IOL model should be implanted. As pointed out by Savini et al,56 however, an IOL with a given cylindrical power would correct the available amount of cylindrical power at the corneal plane. This depended on the distance between the 2 refracting lenses in the eye—the cornea and the IOL. Furthermore, they pointed out that the Alcon Acrysof Web-based toric calculator, which was used for the popular Acrysof toric IOL, estimated a fixed ratio (1.46) between the cylindrical power in the IOL plane and the cylindrical power in the corneal plane. This ratio was based on an average pseudophakic eye and the distance between the cornea and the IOL plane.
In a theoretical study, the authors aimed to evaluate the ratio between the toricity at the corneal and IOL planes. Meridional analysis was applied to an eye model with keratometry (K) ranging from 38.0 to 48.0 D and an axial length (AL) ranging from 20 to 30 mm.
For each diopter of keratometry and each millimeter of AL, the ratio between the toricity at the IOL plane and the toricity at the corneal plane was computed. A short eye (21.00 mm), a medium eye (23.65 mm), a medium-long eye (26.50 mm), and a long eye (28.00 mm) were tested along with different keratometry values.
The authors found that the ratio between toricity at the IOL and corneal planes was not fixed. The highest value was found in the eye with the steepest keratometry (48.0 D) and longest AL (30 mm), where the ratio was 1.86. The lowest value was found in the eye with the flattest keratometry (38 D) and shortest AL (20 mm), where the ratio was 1.29. In general, a low ratio (≤1.41) between toricity at the IOL plane and the corresponding toricity at the corneal plane (due to a flat K or short AL) resulted in overcorrection of astigmatism relative to the value reported by the manufacturer’s online calculator. In contrast, a high ratio (≥1.60) (due to a steep K or long AL) resulted in undercorrection of astigmatism. This variability would, again, be more relevant in eyes with more than 4 D of astigmatism.
The authors discussed that while the Acrysof toric IOL was reported to provide excellent correction of astigmatism with very good performance, the Web-based IOL calculator assumed a fixed ratio of 1.46 between IOL plane and corneal plane toricity. Although this worked well for the average eye, it could be a source of inaccurate predictions in eyes with steep or flat corneas, as well as extremely long or short eyes.
Surgeons need to understand that the ratio between the IOL and the corneal plane toricity depends on the anterior chamber depth. This, in turn, is dependent on the keratometry and AL. The authors also recommend that in cases of “out of average” K and AL values, surgeons could resort to alternate calculators such as the Alpins calculator or the Holladay 2 IOL consultant software.
Hoffmann et al57 published a study to evaluate the predictability of keratometric and anterior/posterior topographic measurements for the improvement of accuracy with toric IOLs. These IOLs were implanted in 78 eyes. Data acquired by the Lenstar optical biometer topography (Tomey, Nagoya, Japan) were processed using the ray tracing software OKULIX to predict the residual refraction. Four different inputs were examined: keratometry only, anterior topography, anterior and posterior topography/tomography, and combination of keratometry only and anterior and posterior topography/tomography. Four weeks postoperatively, the spherical prediction error and the cylindrical prediction error (difference vector between predicted and achieved cylindrical refraction) were determined. Cylindrical prediction errors were 0.57 D (keratometry only), 0.56 D (anterior topography), 0.56 D (anterior and posterior topography/tomography), and 0.50 D (combination of keratometry only and anterior and posterior topography/tomography). Based on their results, the authors concluded that a combination of keratometry and anterior and posterior topography/tomography of anterior and posterior surfaces yielded the best results for toric IOL power calculations.
While calculating the toric model to correct a particular amount of corneal astigmatism, adjustments need to be made based on the predicted anterior chamber depth or the effective lens position, which is a function of both keratometry values and AL. Therefore, the ratio of cylindrical power between the corneal plane and IOL plane is not a fixed entity and is likely to vary. This may lead to prediction errors in eyes that are very short or long or those that have unusually steep or flat corneas. Furthermore, considering the anterior and posterior topography can help improve outcomes.
Surgically Induced Astigmatism
An understanding of SIA has become very important for success with toric IOLs. Although IOL power calculations have improved, the surgical procedure is still the main cause of corneal changes.58 This could possibly explain variations in the final refractive results in some cases and lack of predictability and reproducibility in visual outcomes. It is well known that the location and width of the incision are important determinants of SIA.59,60 However, there are several unknown factors that also affect refractive changes in the cornea.
Denoyer et al61 studied morphological, optical, and biomechanical properties of the cornea to determine new parameters influencing refractive outcomes of cataract surgery. Patients scheduled for cataract surgery were assessed for SIA and HOAs. They were also subjected to corneal imaging using optical coherence tomography and biomechanical analysis by the Ocular Response Analyzer preoperatively and 1, 7, and 30 days postoperatively. The corneal thickness; incision width, length, and architecture; corneal hysteresis; and corneal resistance factor were computed. Cataract surgery was performed through incisions of either 2.75 or 2.2 mm or less.
The authors enrolled 40 eyes in the study. Surgically induced astigmatism and HOAs were significantly lower with smaller incisions. The corneal resistance factor was significantly reduced with a single-plane corneal incision compared with a 3-plane incision. Multivariate analysis showed that SIA was directly correlated with the width of the incision and inversely correlated with corneal hysteresis and corneal resistance factor. The larger incisions had higher amounts of corneal third-order trefoil compared with the smaller ones.
The authors suggested that in eyes with higher corneal hysteresis, SIA may be less despite a larger incision. On the other hand, in eyes with lower corneal hysteresis, SIA may be more even with a smaller incision. A better understanding of corneal biomechanics will help refine outcomes with toric IOLs even further.
Traditionally, we calculate SIA and include it while calculating the net amount of astigmatism to be treated with toric IOLs. Typically, this is done using vector analysis with keratometry values obtained preoperatively and postoperatively. However, we all know that the size and location of the incision play a role in determining SIA. The above article throws light on the role of corneal biomechanics, which may be the reason for unpredictability in visual outcomes even when a perfect surgery has been performed.
Outcomes With Toric Intraocular Lenses—A Review of 4 Studies
In a retrospective study, Hasegawa et al62 studied data from 143 eyes with 1 to 2.5 D of corneal astigmatism. Either aspheric nontoric or aspheric toric IOLs were implanted in the eyes. The authors examined uncorrected distance visual acuity, CDVA, and postoperative refractive astigmatism 3 months after surgery. For the purpose of analysis, corneal astigmatism was subdivided into 3 categories: WTR, ATR, or oblique astigmatism.
A comparison between toric and nontoric IOLs showed no significant difference in CDVA. However, UDVA was significantly better in the toric group compared with the nontoric group (P < 0.0001). As would be expected, the postoperative cylindrical power was also significantly lower in the toric group as compared with the nontoric group. Furthermore, when UDVA was compared between toric and nontoric IOLs based on orientation, the authors reported that with ATR and oblique astigmatism, UDVA was significantly better in the toric group as compared with the nontoric group. In eyes with WTR astigmatism, however, there was no significant difference in UDVA between the 2 groups.
Within the toric group, the residual cylindrical power was significantly lower (P < 0.001) in eyes with WTR astigmatism as compared with eyes with ATR astigmatism. Also, 3 months postoperatively, there was no difference in the axis alignment of toric IOLs between the WTR, ATR, and oblique astigmatism groups.
The mean postoperative UDVA was 0.12 logMAR, which was comparable to reported UDVA of −0.3 to 0.2 logMAR with Acrysof toric IOLs.63–65
The authors performed surgery using a superior incision, which could have resulted in a reduction in WTR in both groups. This may be one of the reasons why the postoperative residual cylindrical power was comparable between toric and nontoric IOLs. In this study, the authors concluded that even with a moderate amount of astigmatism, toric IOLs help in reducing cylindrical power as well as improving BCVA, particularly in eyes with ATR and oblique astigmatism.
Scialdone et al,66 in their prospective, randomized clinical trial, compared refractive and aberrometric results with 2 toric IOLs—the Acrysof toric IOL and the Zeiss AT Torbi 609 M IOL. They randomized 72 eyes into 2 groups—group A, in which the Acrysof IQ SN6AT IOL was implanted, and group B, in which the AT Torbi 609 M IOL was implanted. Three months postoperatively, an evaluation of outcomes included analysis of UDVA and CDVA, the difference between the expected and the obtained astigmatism, the difference between the expected and the obtained spherical equivalent, the difference between the expected and the obtained IOL axis, and optical quality. There were no significant differences between the groups in UDVA, CDVA, or expected versus obtained refractive astigmatism. There were no differences in intraocular or total HOAs. All 72 eyes in the study achieved 0.3 logMAR or better UDVA. The analysis of the difference between expected and obtained astigmatism was not statistically significant. This indicated that the 2 IOLs were equally effective. This is an important issue since the Zeiss toric IOL calculator takes into account anterior chamber depth, central corneal thickness, and IOL spherical power while calculating the effective cylindrical power at the corneal plane. However, the Alcon calculator does not take these parameters into consideration.
Another prospective, nonrandomized study reported by Mencucci et al67 evaluated and compared refractive, aberrometric, and quality-of-life results in 120 eyes divided into 3 groups based on their topographic corneal astigmatism. Group 1 had eyes with of more than 1.5 D of corneal astigmatism that received nonaspheric toric IOLs; group 2 had eyes with more than 1.5 D of corneal astigmatism that received nonaspheric monofocal IOLs; and group 3 had eyes with less than 1.0 D of corneal astigmatism that received nonaspheric monofocal IOLs. Group 3 acted as the control group. The authors compared UDVA, postoperative spherical equivalent, refractive astigmatism, lower-order astigmatism as assessed by aberrometry, Strehl ratio, and modulation transfer function between the groups 3 months postoperatively. Quality of life was also assessed using the NEI Refractive Error Quality of Life Instrument-42 questionnaire. They reported that postoperative UDVA, mean cylindrical power, spherical equivalent, Strehl ratio, modulation transfer function, and lower-order astigmatism were significantly lower in the toric group as compared with the astigmatic nontoric group. These outcomes, however, were not significantly different while comparing the control group with the toric group. The authors also reported a mean rotation of only about 3 degrees. The results of the self-administered questionnaire showed that both the toric and the control groups reported superior clarity of vision, distance vision, ability to cope with glare, and satisfaction with correction as compared with the astigmatic nontoric group.
As has been widely reported in literature, rotational stability with toric IOLs is of crucial importance in their success and ability to improve UDVA. Several factors, including IOL material, design, bioadhesiveness, and complete anterior capsule overlap may be responsible for rotational stability of toric IOLs.
Bachernegg et al68 reported rotational stability with a new toric IOL, the Bi-Flex T aspheric IOL (Medicontur Medical Engineering Ltd Europe (Switzerland, Hungary)). In their prospective series involving 30 eyes, this IOL, which is made up of hydrophilic acrylic material and has double-loop haptics, with an overall diameter of 13.0 mm and optic diameter of 6.0 mm, was aligned intraoperatively using the SMI Surgery Guidance Unit. Postoperatively, rotation from this position (judged from an intraoperative photograph) was assessed at 1 day and 1 and 3 months. The authors reported a mean rotation of 2.12 ± 3.45 degrees (range, −2 to +5 degrees) from end of surgery to last follow-up. However, most of this rotation was between the time of surgery and the first postoperative day, coined as misalignment by them. Minimal rotation occurred between 1 day and 3 months. Ninety percent of the IOLs were within ±2 degrees of the intended axis.
In the study by Bachernegg et al, the authors have not described in detail the methodology used to determine the postoperative IOL axis. Whether the retroillumination photographs were used in conjunction with any software has also not been mentioned. Their results correlate with recently published literature69–76 and once again reiterate the fact that with a better understanding of techniques and technology, toric IOLs are rotationally stable and therefore should be considered for all patients with significant amounts of corneal astigmatism.
Overall, the results of all the 4 previously mentioned studies corroborate our existing knowledge and experience that toric IOLs are both effective and rotationally stable. They should be considered for patients with regular corneal astigmatism associated with cataracts to improve visual, refractive, aberrometric, and quality-of-life aspects.
Toric Intraocular Lenses in Special Situations—A Review of 4 Studies
Parikakis et al78 reported a series of 3 cases with cataract and high astigmatism due to nonprogressive KC (2 eyes) or PMD (3 eyes). The patients underwent cataract extraction and toric IOL implantation (Greece ectasia and toric article). They found that all patients showed a marked improvement in BCVA and subjective refraction. Corneal topography findings remained stable during the follow-up period of 18 to 28 months.
Therefore, toric IOL implantation seems to be an effective method for correcting high astigmatism in cataract patients with stable KC and PMD.
Emanuel et al79 reported 2 cases, in which there was decentration of Acrysof toric IOLs placed in the bag. The authors performed scleral fixation of the haptics using 10-0 nylon sutures. They reported that 30 months after surgery, both IOLs were stable.
Gimbel et al80 reported a case, in which they performed reverse capture of a single-piece toric IOL with both haptics in the bag. The optic was captured through anterior capsulorhexis to stabilize an otherwise rotationally unstable IOL placed in the bag. They reported excellent UDVA and a stable IOL 2 years after surgery.
However, issues such as tilt and misalignment of the IOL also need to be considered before any recommendations can be made in such situations.
Although the performance of toric IOLs has been well documented, there is not much information on the refractive and stability outcomes of these IOLs in vitrectomized eyes.
Lee et al81 reported a retrospective, comparative case series of eyes undergoing combined cataract surgery and microinvasive vitrectomy surgery in patients with coexisting cataract, astigmatism, and vitreoretinal diseases. On examination, 24 months after surgery, eyes with toric IOLs reported better UDVA, residual refractive cylindrical power, and good rotational stability. The mean IOL rotation was 3 degrees, and maximum rotation was 10 degrees.
Thus, toric IOLs can be considered in selected special situations. However, proper patient selection, management of patient expectations, and evaluation of results in these cases are crucial.
Toric Intraocular Lenses and Quality of the Grating Target in Model Eyes
An increase in the number of eyes implanted with toric IOLs increases the probability that vitreoretinal surgery will have to be performed on some of these eyes in the future. Thus, it is important to know what the retinal images will be like during vitreous surgery performed on eyes with toric IOLs.
In eyes implanted with multifocal IOLs of a specific optical design, surgeons who have performed intraocular surgery reported difficulties caused by the blurring of parts of the images of the fundus.82–87 Cylindrical aberrations caused by toric IOLs could distort the retinal image or reduce stereopsis during surgery.
Inoue et al87,88 reported a laboratory study, in which they compared the quality of grating targets viewed through toric and nontoric IOLs placed in the model eye. Toric IOLs from 2 manufacturers (Alcon and Hoya) with a cylindrical power of 3 and 6 D were studied. Nontoric IOLs from the same manufacturers were used as controls. All IOLs had a spherical power of +20 D. Two fundus viewing systems were tested—the wide-angle system and the flat contact lens system. A grating target was glued to the posterior surface of the model eye at the position of the retina. The target consisted of gratings of different orientations and spatial frequencies. The grating target was photographed with a digital camera through a surgical microscope.
The results showed that toric IOLs affected the contrast of the grating target viewed through flat contact lenses, especially at lower spatial frequencies. However, it did not affect the grating target viewed through wide-angle lenses at all spatial frequencies. They further discussed that as light through the wide-angle viewing system passed only through the central optics of the toric IOL, it had lower cylindrical aberration. This was the reason why the wide-angle viewing system was not affected by toric IOLs. On the other hand, with the flat contact lens system, the light passed through all the optics of the IOL, depending on the IOL and the diameter of the pupil.
Toric IOLs have different refractive powers at each point of the lens that the light passes through, and therefore the images have different magnifications along the flat and steep meridians. The spherical power of toric IOLs at each given point is different because of the cylindrical power of the IOL. Fusion of these disparate images can be achieved if the difference in magnification between the 2 eyes does not exceed 5%. In an astigmatic eye, the difference in magnification should not exceed 5% for any meridian, if fusion of the retinal images is to be preserved.20
The images through toric IOLs of high cylindrical power with flat contact lenses were magnified by 3% to 5% in the direction of the steep meridian of the toric IOL and were minimized by 3% to 5% in the direction of the flat meridian. On the other hand, the images through the toric IOL with 6-D cylindrical power with wide-angle contact lenses were not magnified or minimized by more than 1% in any direction. Based on these results, the authors suggested that the commercially available toric IOLs, even with the highest cylindrical power, would not interfere with stereopsis during surgery with either the flat contact lens system or the wide-angle viewing system because the magnification and minimization of the retinal images were less than 5%. However, because the wide-angle viewing system was not influenced by the differences in the cylindrical power of toric IOLs, this system may be recommended for use in eyes with toric IOLs.
This study draws the attention of both cataract and vitreoretinal surgeons to the fact that toric IOLs are theoretically prone to affect retinal viewing during surgery. However, with the current high-powered toric IOLs, this interference is minimal, particularly when using wide-angle viewing systems. Vitreoretinal surgeons might want to keep this in mind while planning surgery in such patients.
MULTIFOCAL INTRAOCULAR LENSES
Cataract surgery with IOL implantation, in the present day scenario, aims to achieve an improvement in a patient’s visual acuity, as well as spectacle independence.
The limitation of the monofocal IOL design is that it allows the patient to achieve either distance, intermediate, or near vision, thereby not encompassing both distance and near vision. The earliest multifocal IOLs designed to achieve good vision at all distances were introduced in the 1980s.89,90
Multifocal IOLs using refractive, diffractive, and combinations of both optical principles have been developed. More recently, aspheric multifocal IOLs have been introduced, which result in superior91 or equal92 visual performance compared with spherical multifocal IOLs.
Choosing the Right Type of Intraocular Lens for the Right Patient: A Review of 2 Studies
Apart from refractive versus diffractive designs and spherical versus aspherical designs, multifocal IOL designs can be described as pupil dependent or pupil independent.
A recent review article by de Vries et al93 described the available designs, results, and adverse effects of implanting multifocal IOLs following cataract surgery.
Choosing the right multifocal IOL can be a challenging task if the goal is for the patient to achieve spectacle independence. Not every available IOL is suitable for every patient because of the complexity of different lifestyles, patient requirements, and the inherent anatomical and physiological traits of different eyes.
Braga-Mele et al94 recently published a review, which recommended some best practices, which could be used while choosing multifocal IOLs for patients after cataract surgery. According to the authors, the primary requirement was to understand the patient’s lifestyle needs and visual expectations after surgery. The next step was to choose an IOL based on its functional benefits and limitations keeping in mind patient expectations. However, the authors warned that even the best of surgeries or accurate measurements or formulae may give rise to residual refractive errors postoperatively, and patients should be counseled preoperatively to expect these outcomes.
Multifocal Intraocular Lenses in the Presence of Corneal Astigmatism—A Review of 3 Studies
Postoperative astigmatism can be a major refractive problem in patients with multifocal IOLs. It reduces UCVA, causes patient dissatisfaction, and frequently requires additional refractive surgery.95,96 With multifocal IOLs, any astigmatism over 1.00 D should be corrected for best results.96 The introduction of multifocal toric IOLs has opened up the possibility of multifocality to individuals with coexisting regular astigmatism undergoing cataract surgery.
Ferreira et al97 evaluated the visual and wavefront outcomes after cataract surgery with implantation of a diffractive multifocal toric IOL. The objective of this study was to evaluate visual function after implantation of the Acrysof IQ Restor multifocal toric IOL (Alcon Laboratories, IncAlcon Laboratories, Texas, USA) in patients with cataract and regular astigmatism between 0.75 and 2.5 D and IOL power calculation between +6.00 and +30.0 D.
This prospective case series was performed at 2 clinical centers. It included 38 eyes of 19 patients. A preoperative examination included a complete ophthalmologic examination of UDVA, corrected distance visual acuity, uncorrected and corrected intermediate visual acuity, and uncorrected and corrected near visual acuity using logMAR acuity charts under photophic conditions. Manifest refraction, slit-lamp biomicroscopy, Goldmann applanation tonometry, and fundoscopy under cycloplegia were done.
Appropriate IOL power calculations, using the standardized formulas, ultrasound biometry, and keratometry using a Pentacam-rotating Scheimpflug imaging device, were carried out. The IOL cylinder power and axis placement were calculated using the online Acrysof ReSTOR toric calculator. A single surgeon performed all surgeries under topical anesthesia using a standardized, coaxial phacoemulsification technique. Postoperative examinations were performed at 1 day, 1 week, and 1, 2, and 3 months using the same tests as for the preoperative examination. The Mann-Whitney U test was used to compare preoperative and postoperative results. The intraclass correlation coefficient was calculated as a measure of intraobserver repeatability.
There was no statistical significance in visual outcomes across all the examinations during follow-up visits (P> 0.05). All patients were spectacle independent. Spherical refraction was within ±0.5 D of the attempted spherical correction in 33 eyes. It was within ±1.00 D in all eyes. The refractive cylindrical power was ± 0.5 D in 30 eyes (79%) and ±1.00 D in 37 eyes (97%). During the early postoperative period, 1 eye required a second surgery to align the IOL axis so as to achieve a postoperative rotation of 15 degrees. At 3 months postoperatively, the mean toric IOL rotation was 2.97 ± 2.33 degrees. The HOAs, root mean square, coma, spherical aberrations, Trefoli, and Strehl were similar to those reported by a recent study of the monofocal lens design. The dysphotopic phenomena were comparable to those reported for the nontoric version of the Acrysof ReSTOR IOL.
In another multicentric observational study by Bellucci et al,98 patients with bilateral cataract and astigmatism undergoing cataract surgery with implantation of an AT Lisa toric 909 M multifocal toric IOL (Carl Zeiss Meditec, Germany) underwent postoperative evaluations for UDVA (Early Treatment Diabetic Retinopathy Study chart at 4 m), intermediate visual acuity (60 and 80 cm using the Precision Vision 2000 chart), and near visual acuity (40 cm using the Precision Vision 2000 chart). They were also evaluated for refraction, IOL rotation, defocus curve, and contrast sensitivity testing.
The multifocal toric IOL was implanted in 284 eyes of 142 patients. At 6 months, 89.4% of eyes were within ±1.00 D of emmetropia. The mean refractive cylinder decreased from −2.39 ± 1.48 to −0.49 ± 0.53 D. It was lower than 1.00 D in 80.9% of eyes. The mean visual acuities (logMAR) were monocular UDVA of 0.16 ± 0.22, monocular CDVA of 0.04 ± 0.15, binocular CDVA of −0.00 ± 0.09, monocular uncorrected near visual acuity of 0.21 ± 0.22, monocular corrected near visual acuity of 0.08 ± 0.16, and binocular distance corrected near visual acuity of 0.07 ±0.14. The intermediate visual acuity at 60 cm (80 cm) was as follows: monocular UCVA of 0.16 ± 0.21 (0.09 ±0.21), monocular distance corrected visual acuity of 0.13 ± 0.19 (0.07 ± 0.20), and binocular distance corrected visual acuity of 0.07 ± 0.17 (0.00 ± 0.18). At 3 and 6 months, 95.8% of IOLs showed no rotation greater than 5 degrees. Overall, the IOLs were found to be rotationally stable, and they provided excellent unaided vision at all distances. In eyes with a preoperative astigmatism that was less than 1.00 D, the resulting final cylindrical power was similar to that obtained in other studies with spherical IOLs. The contrast sensitivity performance too was found to be comparable to the nontoric multifocal model made by the same manufacturer. The depth of focus was also reported to be similar to the nontoric multifocal model.99,100
Venter and Pelouskova102 reported a case series to evaluate refractive outcomes and rotational stability after implantation of multifocal toric IOLs with a surface-embedded near section. Three months postoperatively, the mean monocular UDVA was 0.03 ± 0.11 logMAR, and the mean binocular UDVA was −0.02±0.10 logMAR. The mean monocular uncorrected near visual acuity at 40 cm was 0.17±0.14 logMAR, which was approximately Jaeger 3 (J3). Binocularly, the mean uncorrected near visual acuity was 0.13 ± 0.12 logMAR (approximately J2). At 3 months postoperatively, 84.3% of eyes were within ±0.50 D, and 97.7% were within ± 1.00 D of the spherical equivalent. On administering a patient satisfaction questionnaire, as expected with any multifocal IOL design, a percentage of patients experienced difficulty with glare, driving at night, starbursts, and a halo effect around lights. A small number of patients also reported ghosting and doubling of vision. Intermediate vision (computer, dashboard) seemed to be less of an issue than reading small print seen on medicine bottles, telephone books, and newspapers.
Results of Multifocal Intraocular Lens Implantation—A Review of 2 Studies
A prospective interventional study by Stephanie Schmickler et al102 evaluated 104 eyes of 52 patients aged 68.5 ± 10.5 years, who underwent cataract surgery. The patients were bilaterally implanted with aspheric diffractive TECNIS multifocal single-piece IOLs (AMO, CA), model ZMBOO, after completing a questionnaire regarding their visual symptoms, use of visual correction, and their visual satisfaction. This was a multicentric study carried out across 5 European centers. Postoperative assessments of the second eye were carried out 4 to 6 months after surgery in addition to routine postoperative examinations.
The overall rating of vision without spectacles was 8.5 ± 1.1 out of 10 after surgery, compared with 4.7 ± 2.1 before surgery. The IOL used enabled a good level of distance and near visual acuity over a wide range of working distances. This was reduced by only half a logMAR acuity line under mesopic conditions, despite a 1.5-mm change in pupil size, highlighting the fact that diffractive optics are pupil independent. The reading speed achieved was averaged at 121.4 ± 30.8 as compared with that previously reported with monofocal and multifocal IOL optics. The authors concluded that the TECNIS multifocal single-piece IOLs (AMO, CA), model ZMBOO, gave a high level of spectacle independence, low residual refractive error, high distance, and near visual acuity in photopic and mesopic lighting conditions and good reading acuity and speed, resulting in high levels of patient satisfaction.
In a retrospective study of 22 eyes of 21 patients, Veseta et al103 analyzed reasons (14) for IOL explantation. The authors divided the study population into 2 groups. Group A had explanted monofocal IOLs, and group B had explanted multifocal IOLs. Reasons for IOL explantation in group A were incorrect IOL power, IOL subluxation, decentration, and IOL opacity. Reasons for explantation in group B were intolerable haloes, glare, incorrect IOL power, and postoperative expectations not being met. Therefore, careful patient selection, sound surgical techniques, optimally selected IOL power, precise biometry readings, and high quality of IOL materials play an important role in minimizing the risk of IOL explantation.
Performance of Multifocal Intraocular Lenses Versus Monofocal Intraocular Lenses
Yamauchi et al104 compared the visual performance of multifocal and monofocal IOLs made of the same material. In this study, 46 patients were implanted with multifocal IOLs bilaterally (ZMA00: 32 patients; ZMBOO: 14 patients), and 85 patients were implanted with monofocal IOLs bilaterally (ZA9003: 47 patients; ZCB00: 38 patients). The mean ages of the patients in the 2 groups were 67.46 ± 7.56 and 67.84 ± 5.89 years, respectively. There were no significant differences between the 2 groups in terms of the patients’ age or sex (P = 0.7442 by Student t test and P = 0.9797 by the χ2 test, respectively.)
There was no statistically significant difference in UDVA, uncorrected intermediate visual acuity, or CDVA. Uncorrected intermediate visual acuity was significantly better in the multifocal group, whereas corrected intermediate visual acuity and corrected near visual acuity were better in the monofocal group. Contrast sensitivity was significantly better in the monofocal group as compared with the multifocal group (both with and without glare). Spectacle dependency was also lower in the multifocal group. The subjects who were evaluated for their driving scores were patients who drove on a daily basis (30 patients in the multifocal group and 49 patients in the monofocal group). There were no significant differences between the groups. There was just 1 question related to nighttime driving, in which the monofocal group significantly outperformed the multifocal group. In terms of pupillary sizes and ocular aberrometry, there were no significant differences between the 2 groups.
The patients answered the Visual Function Questionnaire designed by the National Eye Institute. Twenty-five scores exhibited no significant differences between the 2 groups. The only exception was that the nighttime driving scores were less problematic in the monofocal group. These results demonstrated that the multifocal IOLs used in this study decreased spectacle dependency of patients without compromising subjective visual function.
Newer Multifocal Lenses—A Review of 2 Studies
A new trifocal diffractive IOL has been designed combining 2 superimposed diffractive profiles—one with +1.75 D addition for intermediate vision and the other with +3.50 D addition for near vision.
Vryghem et al105 evaluated subjective and objective visual results after implanting this new trifocal diffractive IOL. This study included 50 eyes of 25 patients operated on by a single surgeon. The uncorrected and best CDVAs; monocular and binocular vision and near, intermediate, and distance visual acuities; contrast sensitivity; and defocus curves were measured 6 months postoperatively. In addition to the standard clinical follow-up, a questionnaire evaluating individual satisfaction and quality of life was given to the patients.
The mean age of the patients at the time of surgery was 70 ± 10 years. The mean uncorrected and corrected monocular distance visual acuities were 0.06 ± 0.10 logMAR and 0.00 ± 0.08 logMAR, respectively. The outcomes for the binocular UDVA were almost the same (− 0.04 ± 0.09 logMAR). The binocular uncorrected intermediate and near visual acuities were – 010 ± 0.15 logMAR and 0.02 ± 0.06 logMAR, respectively. The distance corrected visual acuity was maintained under mesopic conditions. The contrast sensitivity was similar to that obtained after implantation of a bifocal IOL and did not decrease under mesopic conditions. The binocular defocus curve confirmed good visual acuity, even in the intermediate distance range, with a moderate decrease of less than 0.2 logMAR at −1.5 D, with respect to the best distance visual acuity at 0-D defocus. Patient satisfaction was high. There was no evidence of any discrepancy between the objective and subjective outcomes.
Based on their results, the authors concluded that the introduction of a third focus in diffractive multifocal IOLs improved the intermediate vision with minimal visual discomfort for the patients.
There are very few published data available on in vivo clinical outcomes with trifocal IOL designs. The study described below is one of the very few studies available in literature on the use of trifocal IOLs. To the best of our knowledge, it represents the largest cohort evaluated with FINEvision IOLs.
FINEvision IOLs are single-piece, aspheric diffractive trifocal IOLs composed of 25% hydrophilic acrylic material. The overall IOL diameter is 10.75 mm, and the optic is 6.15 mm. The IOL is available in powers ranging from +10.0 D to +30.0 D in 0.50-D steps. The intermediate vision and near vision add powers are +1.75 and +3.50 D respectively.
Sheppard et al106 assessed clinical visual outcomes and the patients’ subjective experiences after bilateral implantation of FINEvision trifocal diffractive IOLs.
The authors evaluated 30 eyes of 15 patients. All patients underwent uneventful bilateral cataract surgery. The IOLs were well centered in all eyes. There was no pupillary distortion or iris trauma.
The mean monocular spherical refractive correction was 0.27 ± 0.36 D (range, −0.25 to +1.00 D), and the cylindrical correction was −0.45 ± 0.45 D (range, 0.00 to −1.50 D). Under photopic and mesopic conditions, optimum visual acuity results were obtained at 0.00-D defocus (equivalent to distance vision viewing) with a second peak at −2.5 D (equivalent to near viewing at 40 cm). No distinct peak in the intermediate zone was present for either lighting level, although the range of clear vision (0.3 logMAR or better) extended from +1.00 to −2.50 D of defocus, with no sharp drop in visual acuity in the intermediate zone under photopic conditions. Binocular contrast sensitivity values were significantly better than monocular values at all spatial frequencies tested (P < 0.05). There were no significant differences in contrast sensitivity values between the right and left eyes at any spatial frequency (P > 0.05). Postoperatively, none of the patients reported any adverse photic phenomena.
The ear Activity Visual Questionnaire scores for subjective satisfaction with near vision were high, with a mean Rasch score of 15.9 ± 10.7 U [0 = completely satisfied; 100 = completely unsatisfied (range, 0–33.3)]. The mean overall satisfaction score with near vision (0 = completely satisfied, 4 = completely unsatisfied) was 0.7 (range, 0–2).
There have been only 2 studies carried out to report clinical outcomes in a cohort of patients with binocular implantation of diffractive trifocal IOLs, and this is one of them. The mean monocular UDVA (0.19± 0.09) and CDVA (0.08 ± 0.08) results are similar to the values reported by Voskresenskaya et al.107
In conclusion, FINEvision trifocal IOLs provided a good standard of distance vision acuity and intermediate and near visual function, as shown by the defocus curve testing, without any reports of dysphotopsia.
Evaluation of a Surgically Adjustable Multicomponent Intraocular Lens
Portaliou et al108 reported a 2-year follow-up of an initial clinical evaluation of a novel design multicomponent IOL called the Infinite Vision Optics multicomponent IOL. This is a hydrophilic, acrylic, foldable, optically integrated lens system that enables customized correction of all degrees of sherical, cylindrical, and multifocal power during primary surgery. At the same time, multicomponent IOLs allow adjustment of all residual refractive errors at any time postoperatively by the surgical exchange of one of the IOL components. It can also be used to manage patient expectations, including presbyopia correction.
This was a case series of 6 patients with a mean age of 63.3 years, who underwent routine cataract surgery and multicomponent IOL implantation. The primary objectives of the study were to evaluate the manufacturing feasibility of the IOL, the surgical implantation technique, and the evidence of interlenticualar fibrosis.
All 6 patients had uneventful cataract surgeries by a single surgeon using a standardized technique. The multicomponent IOL ocular system (Infinite Vision Optics, Strasbourg, France) implanted in all patients had 2 components. The base IOL or posterior component had a plate haptic configuration and was designed to be placed in the capsular bag. It allowed spherical corrections only. The anterior component of the IOL had 2 haptics designed to fit with a small bridge that projected off the anterior surface of the base IOL to secure the front IOL to the base IOL in a piggyback fashion. This anterior component of the IOL had 2 very thin IOL sections held together by hydrostatic forces that allowed spherical, cylindrical, and multifocal primary corrections or adjustments of residual refractive error. The anterior component of the IOL was implanted in the sulcus.
Two years postoperatively, the results showed a statistically significant improvement in UDVA and CDVA. None of the patients required enhancement surgery. There were no statistically significant differences in endothelial cell density as compared with endothelial cell density loss after routine cataract surgery. There was no posterior capsule opacification and no interlenticular fibrosis in any eye. However, this small initial series does not report outcomes related to inflammation or glaucoma.
Appropriately selected patients can achieve spectacle independence and good near and distance visual outcomes with current multifocal IOLs. Proper patient education and customization of IOL after weighing the benefits and adverse effects of multifocality are of paramount importance. Despite this, some patients will have unsatisfactory outcomes. Suitable postoperative management of both satisfied and dissatisfied patients will ultimately improve the visual benefits of multifocal IOLs.
With newer multifocal and trifocal IOL designs, and with added toricity of multifocal IOLs, the spectrum for implantation as well as customizing visual outcomes based on patient expectations is expanding.
The studies outlined in this review represent only a small proportion of the articles published over the course of the academic years 2012–2013. However, these studies report promising outcomes with FS laser–assisted cataract surgery and also open up newer avenues to achieve enhanced visual and refractive outcomes with toric and multifocal IOLs. Some of the articles corroborate and endorse our understanding of these technologies, whereas others bring out hitherto unexplored subjects such as corneal biomechanics and SIA and the contribution of the posterior cornea in overall corneal astigmatism.
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