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Effectiveness and safety of femtosecond laser–assisted lens fragmentation and anterior capsulotomy versus the manual technique in cataract surgery

Reddy, Kasu Prasad MB, DO, MRCOphth(UK)*; Kandulla, Jochen PhD; Auffarth, Gerd U. MD, PhD, FEBO

Author Information
Journal of Cataract & Refractive Surgery: September 2013 - Volume 39 - Issue 9 - p 1297-1306
doi: 10.1016/j.jcrs.2013.05.035
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Abstract

Cataract accounts for up to half the cases of blindness worldwide, making it the most frequent cause.A Most important, cataract is also the main cause of easily curable blindness. Not surprisingly, the cataract surgery rate is highest in developed countries.A In 2011, the estimated number of cataract surgeries was approximately 3.3 million in the United States and more than 19 million worldwide.A–C

Modern cataract surgery has been characterized by ongoing advancements (eg, change from intracapsular to extracapsular extraction, use of phacoemulsification, and miniaturization of instrumentation) and by the development of new types of intraocular lenses (IOLs).1 Along with these changes has been a progressive reduction in incision size so that microincision cataract surgery can now be performed. Together, these advances are considered to have improved overall outcomes.

Nevertheless, cataract surgery presents continuing challenges and risks despite its overall safety. Specifically, manual capsulorhexis (anterior capsulotomy), considered the most difficult part of the procedure, is highly dependent on the surgeon’s skill.2,3 Potential complications include injuries to the cornea, iris, and the anterior or posterior capsule as well as vitreous loss. Capsule complications are positively associated with poorer long-term outcomes.4 In addition, the size, precision, and centration of the capsulorhexis can have a substantial impact on ultimate visual outcomes.5 In addition to challenges associated with manual capsulorhexis, excess energy that occurs during phacoemulsification can cause capsule complications and damage the corneal epithelium at the probe insertion site.5,6

Femtosecond lasers are being used to address some of the remaining issues associated with manual cataract surgery. In general, femtosecond lasers can improve precision and reduce risks.2,5,7,8,D

The objective of this study was to evaluate the effectiveness and safety of femtosecond laser–assisted lens fragmentation for cataract surgery. Specifically, the study aimed to determine whether femtosecond laser prefragmentation of the lens reduces the duration of applied ultrasound (US) energy during phacoemulsification and to compare the adverse event profile of laser prefragmentation with that of standard manual phacoemulsification. The precision of the capsulotomy was also assessed in both study groups.

Patients and methods

This randomized controlled open-label prospective single-center multisurgeon trial (4 surgeons) included 2 treatment groups: (1) femtosecond laser–assisted lens fragmentation and anterior capsulotomy before phacoemulsification (laser group) and (2) manual capsulorhexis and standard phacoemulsification (manual group). The study conformed to the Declaration of Helsinki, and local independent ethics committee (Aditya, India) approval was obtained. All patients provided informed consent.

Eligible patients were at least 18 years old with clear corneal media and elected to have routine cataract surgery. Figure 1 shows the key exclusion criteria.

Figure 1
Figure 1:
Exclusion criteria.

Examinations

Preoperative eye examinations took place 30 days to 1 hour before treatment. Preoperative assessments included corrected distance visual acuity (CDVA), cataract grade and type, slitlamp and fundus examinations, and intraocular pressure. Cataracts were graded at the slitlamp (SL10E, Topcon Corp.) according to the Lens Opacities Classification System III.9 The study protocol exclusion criteria for the femtosecond laser procedure included anterior chamber depth (ACD) of less than 2.4 mm or more than 4.5 mm. Therefore, the laser group also had corneal mapping and measurement of ACD, axial length, and lens thickness.

Postoperative slitlamp, visual, and fundus examinations were performed on the day of surgery and 1 day postoperatively (16 to 36 hours).

Laser System

The study was performed using the Victus femtosecond laser platform (Bausch & Lomb Technolas). Femtosecond lasers from Technolas have been available since 2004 for flap creation; therapeutic applications for femtosecond lasers followed thereafter.10–19,E The laser system includes a curved patient interface that adapts to the natural curvature of the cornea. The patient interface works in combination with pressure sensors that monitor pressure and shear forces on the eye in 3 dimensions (xy plane and along the anterior–posterior axis) to minimize corneal applanation and avoid corneal wrinkles. The laser uses a real-time optical coherence tomography (OCT) imaging system for procedural planning and real-time monitoring. For cataract procedures, the laser uses a pulse rate of up to 80 kHz; for flap procedures, the pulse rate is up to 160 kHz.10,E

Surgical Technique

Both femtosecond laser–assisted and manual procedures were performed by experienced surgeons. These procedures included access incisions for the surgical tools, anterior capsulotomy, phacoemulsification, and IOL implantation.

The study eye was dilated, and topical anesthesia was administered repeatedly before capsulotomy. All surgical procedures were performed using standard surgical equipment. The scleral or corneal incision was made using a keratome knife with a 2.8 mm width. Trypan blue was used to stain the tissue so the capsulotomy was easier to visualize during the femtosecond and manual procedures. The manual capsulorhexis was created using the continuous curvilinear capsulorhexis (CCC) technique. The intended diameter was dependent on pupil size. Video snapshots were used to evaluate capsulorhexis centration in relation to the pupil. After excision, the extracted capsulorhexis was photographed on a scale. The diameter and circularity of the capsulorhexis were evaluated ex situ. The IOLs were placed in the capsular bag using an IOL injector; no suture was used to close the wound.

For the laser-assisted procedure, the desired lens-fragmentation pattern and dimensions as well as the desired capsulotomy diameter were selected using the graphic user interface screen before the patient’s eye was docked to the patient interface on the femtosecond laser platform. Docking the patient’s eye to the optical system via the patient interface is intended to ensure stable positioning of the dissection pattern. The image of the docked eye from an embedded camera and a live OCT image of the crystalline lens with the anterior and posterior capsular bag were displayed on the screen of the graphic user interface. The live OCT allows precise identification of landmarks (eg, anterior and posterior corneal surfaces and lens capsule), ensuring sufficient safety distances to protect tissues. Based on the live data image, the lens-fragmentation pattern and the capsulotomy pattern were defined by adjusting the marked treatment area in the online OCT and the online camera images. An overlay of the planned treatment on the OCT and video images shown on the graphic user interface allowed the surgeon to verify the treatment.

Phacoemulsification was performed using the Stellaris Vision Enhancement System (Bausch & Lomb). After anterior capsulotomy was performed, lens fragmentation was applied in different patterns as follows: cross only, ring only, quadrant only, or a combination. The capsulotomy and lens-fragmentation cuts were programmed to proceed from posteriorly to anteriorly. This upward propagation of the laser beam focus avoids shielding effects by bubbles with the goal of ensuring precise cutting of the ocular media. In addition, it reduces the laser radiation reaching the retina. The dimensions of lens fragmentation were individualized for each patient. The boundaries of the lens-segmentation pattern were overlaid as a trapezoid graphic on the live OCT image of the eye, which allowed the surgeon to select the safety zones appropriate for the crystalline lens of each eye (Figure 2). A safety distance of at least 800 μm from the posterior capsular bag and 200 μm from the anterior capsular bag was maintained to avoid intraoperative complications. (Note: A safety distance of 600 μm from the anterior capsular bag is now used when the fragmentation diameter exceeds the capsulotomy diameter.)

Figure 2
Figure 2:
Optical coherence tomography image of the human eye.

After the laser procedures, patients were undocked from the laser and moved to the phacoemulsification system. Incisions were made in the cornea or sclera. The circular segment of the capsule was removed with a forceps by grasping the tissue centrally and moving it upward in a circular manner. In this way, any potential remaining bridge connecting the dissected disk with the capsular bag was disrupted; removal by this method is safer than pulling the capsule disk out. After phacoemulsification and extraction of the crystalline lens, the IOL was inserted.

Perioperative Medical Care

Combined diclofenac sodium 1 mg, tromethamine 8 mg, sorbic acid 2 mg, and boric acid 15 mg/1 mL eyedrops (Voveran Ophtha) were started 2 days preoperatively and continued 2 times per day for up to 2 months. Steroids were used for a maximum of 2 months postoperatively, beginning hourly on the first postoperative day and tapering to 4 times daily for up to 2 months. The postoperative schedule for antibiotics was hourly at 1 day, every 2 hours at 2 and 3 days, and 6 times daily at 4 through 7 days.

Outcome Measures

The primary effectiveness endpoint was the effective phacoemulsification time (EPT) during phacoemulsification, which is the time to emulsify and extract the cataractous lens via the phacoemulsification probe if the phaco machine were driven at 100% phaco energy. The EPT represents the cumulative phaco energy used during the phaco procedure. In addition to the EPT, the mean phaco time and mean phaco energy were evaluated. The secondary effectiveness endpoint was a subjective surgeon assessment of the ease of phacoemulsification based on perceived hardness of the nuclear sclerotic cataract on a 5-point scale (1 = very easy; 2 = easy; 3 = middle; 4 = hard; 5 = very hard). Other effectiveness endpoints included the mean phaco time, mean phaco energy, and volume of balanced salt solution used.

Capsulotomy Comparisons

In addition to the phacoemulsification endpoints, the capsulorhexis diameter, relative diameter (measured/intended), circularity, and the extent of decentration were measured. In the laser group, the intended diameter was specified in the graphic user interface and could vary between 5.0 mm and 6.0 mm. In the manual group, the intended diameter was assumed to be 5.5 mm.

The diameter and circularity were measured ex situ. The capsulorhexis margin was delineated manually on photographs in which the blue-stained capsulorhexis had been spread onto a flat surface (Figure 3). An ellipsoid was fitted to the marked points using a software tool (Matlab, Mathworks, Inc.). From the fit, the semimajor (dmajor) and semiminor (dminor) axes were assessed and used to calculate mean diameter and circularity, respectively, whereby the diameter ϕ (ex vivo) was (dmajor + dminor)/2 and circularity ε was dminor/dmajor. This fitting procedure allowed arbitrary orientation of the ellipsoid semimajor axis based on the actual data geometry used for the fit (Figure 3).

Figure 3
Figure 3:
Ex situ capsulorhexis following the laser-assisted procedure (a) and the manual procedure (b). White scale bars indicate 1.0 mm (dmajor = semimajor axis; dminor = semiminor axis).

The diameter predictability was quantified by the relative diameter δϕ, defined as the ratio between ϕ and the intended diameter ϕintended. Because of retraction of the capsular bag, the diameter of the excised capsulorhexis was slightly smaller than the in situ diameter of the capsule cut. It was previously found that the mean excised tissue diameter was 7.48% ± 0.19% (SD) smaller than the in situ diameter of the capsule cut due to capsule contraction (unpublished company data on file with Technolas Perfect Vision). A similar observation was also made by Palanker et al.2 To correct for this difference, 7.48% was added to the measured diameter of the laser capsulotomy.

To assess the deviation from perfect centration, the pupil and the capsulorhexis were delineated manually on in situ snapshots. Ellipsoids were fit to the margins, and the Euclidian distance between the centers of mass was used to calculate ΔR according to equation ΔR = (pupilcenter of mass − capsulorhexiscenter of mass). Figure 4 shows a sample in which the pupil center is indicated by the red symbol and the capsulotomy center by the gray symbol. The contours of the ellipses fit to the pupil, and the outer rim of the capsulotomy are shown as dashed lines and solid lines, respectively. Calibration of each in situ snapshot was required to assess the absolute value ΔR, where the diameter ϕ was used.

Figure 4
Figure 4:
Schematic (a) and in situ snapshot (b) showing the pupil, outer rim of the cut, decentration (ΔR).

Intraocular Lens Decentration

Postoperative determination of IOL decentration was assessed according to whether the capsule overlap was considered to be nonconcentric within the optic diameter on the day of surgery (ie, more than 150 μm). One day postoperatively, assessment of IOL decentration or malposition was determined by visual inspection with a slitlamp examination. The IOL was considered to be centered when there was complete capsule overlap of the IOL optic (ie, for an IOL optical diameter of 6.0 mm and a capsulotomy of 5.5 mm, the decentration was less than 250 μm).

Safety

Safety endpoints were based on adverse events, such as a posterior capsular bag tear, IOL malposition, and iris damage. Serious adverse events related to the treatment procedures were classified by severity and causality.

Statistical Analyses

The planned enrollment was 60 eyes per group (based on sample-size calculations). Differences in between-group means were evaluated by the Student t test or Welch t test, as appropriate. Differences between medians were assessed using the Mann-Whitney U test. The F test was used to evaluate differences in standard deviations, and the Kolmogorov-Smirnov test was used to evaluate differences in distributions. The level for statistically significant differences was set at 5%. Descriptive statistics were used for patient demographics and adverse events.

Results

Demographics and Baseline Characteristics

The study enrolled 131 patients (laser group, 64; manual group, 67). One eye in the laser-assisted group was excluded from analysis because of a protocol violation, resulting in 130 eyes. During the clinical trial, it became evident that the P values of all phacoemulsification parameters (EPT, mean phaco energy, mean phaco time, and balanced salt solution volume) were both surgeon dependent and cataract grade dependent. Evaluation by the Mann-Whitney U test showed that median cataract grade between the 2 treatment groups was equal except for those operated on by 1 surgeon. To ensure equal cataract grade distributions in the 2 study groups to guarantee correct data analysis and rule out preoperative bias, 7 eyes in the laser-assisted group and 4 in the manual group were excluded from further analysis. This resulted in 56 eyes in the laser-assisted group and 63 in the manual group that had subsequent analysis.

Table 1 shows the patients’ demographics and baseline characteristics. There were no demographic differences between groups. In addition, baseline eye characteristics, including cataract grade and type, did not differ significantly between groups (P > .05). Slitlamp and fundus examinations were normal considering the disease state and progression. No cases of epithelial staining or erosion, corneal edema, or anterior chamber cells or flare were observed before cataract surgery.

Table 1
Table 1:
Patient demographics and baseline characteristics.

Surgical Parameters

Of the 119 eyes, 78 (65.5%) had scleral tunnel incisions. For the manual procedure, CCC was performed in 63 eyes. Both IOL haptics were in the capsular bag in all eyes, and no eye required sutures. In the laser group, a variety of lens-fragmentation patterns were used including cross only, rings only, cross plus rings, and quadrant cuts.

Effectiveness

The distribution of EPT differed significantly between the laser group and the manual group (P=.001) (Figure 5). The mean EPT was lower in the laser group (5.2 ± 5.7 seconds) than in the manual group (7.7 ± 6.0 seconds) (P=.025). Surgeon ratings of the ease of phacoemulsification did not differ significantly between the 2 groups (data not shown). The median rating was 2 (easy) in both groups.

Figure 5
Figure 5:
Cumulative percentage of eyes by EPT (EPT = effective phaco time).

The mean phaco energy differed significantly between groups (P<.001). The mean phaco energy was 13.8% ± 10.3% in the laser group and 20.3% ± 8.1% in the manual group. The mean phaco time in the laser group and manual group did not differ significantly (30.4 ± 16.0 seconds versus 34.5 ± 19.6 seconds), nor did the mean balanced salt solution volume (84.6 ± 29. 6 mL versus 86.0 ± 25.8 mL).

Capsulotomy Comparisons

Table 2 shows the capsulorhexis quality measures. The accuracy and predictability of the capsulotomy (with respect to intended diameter, circularity, centration) were significantly better in the laser group than in the manual group (P<.01).

Table 2
Table 2:
Capsulorhexis quality measures.

Safety

Day of Surgery

Table 3 shows the complications on the day of surgery. All events were mild, and the incidence of incomplete capsulotomy did not differ significantly between the 2 groups. The rates of decentered capsulotomy and decentered IOL were significantly higher in the manual group than in the laser group (P<.01).

Table 3
Table 3:
Minor complications on the day of surgery.

One-Day Follow-up

No adverse events were observed in either treatment group. Slitlamp examination showed all IOLs to be centered. Results of slitlamp and fundus examinations and the occurrence of corneal edema were similar in the 2 groups. No cases of epithelial staining/erosion or abnormal iris were observed. Two cases of abnormal fundus examinations were noted in the manual group. One of the patients had previous retinal surgery, and the abnormal findings were also observed during the preoperative examinations. The other patient had early-stage glaucoma. Both findings were deemed unrelated to the present study. The rates of anterior chamber cells and flare were distributed similarly in each group.

Discussion

Excess energy that occurs with phacoemulsification may cause capsule complications as well as damage to the corneal epithelium at the probe insertion site; thus, it is beneficial to try to limit exposure to phaco US energy.5,6 This randomized controlled open-label prospective single-center multisurgeon study compared the use of a femtosecond laser to prefragment the cataractous lens before phacoemulsification with the use of the standard manual approach. We believe this is the first study to compare femtosecond laser cataract surgery using the Victus platform with manual cataract surgery.

We found that femtosecond laser assistance significantly reduced the EPT and mean phaco energy, which is consistent with findings in other studies.2,20–22 Initial results by Palanker et al.2 indicate an approximate 40% reduction in US energy used during phacoemulsification (cumulative dissipated energy) compared with manual cataract surgery. Abell et al.20 report a 70% reduction in mean EPT compared with the manual technique. Studies of femtosecond laser lens fragmentation by Conrad-Hengerer et al.21 found a significant reduction (>96%) in EPT using the femtosecond laser technique compared with the manual technique. The group also found that differences in fragmentation patterns influenced the EPT.22 With growing experience using the femtosecond cataract procedure and optimum use of different fragmentation patterns for different cataract grades, we anticipate being able to further reduce the EPT using this laser system.

In our study, by using phaco settings that matched the expected hardness of the cataractous lens with and without femtosecond laser chopping, surgeons were able to perform phacoemulsification with ease. Even though the surgeons in this study did not rate laser-assisted phacoemulsification to be easier than the manual procedure, laser-assisted phacoemulsification was associated with a lower phaco energy and a shorter EPT. The phacoemulsification technique is highly individualized and dependent on surgeon technique and phaco settings. This, combined with the learning curve associated with adopting this new technique, may explain the current findings.

We observed that transitioning to femtosecond laser cataract surgery requires an adjustment of the phacoemulsification technique and expect that each surgeon will have to adapt to the procedure. The learning curve associated with performing the procedure can vary depending on surgeon experience and training. The level of adjustment to the new technique may have also influenced the outcomes in our study. Based on their experience of more than 1500 cases, Roberts et al.23 concluded that the surgical outcomes and safety of laser cataract surgery improved significantly with surgeon experience, adjustment of techniques, and improved technology.

In our experience, the main differences in phacoemulsification are in irrigation and aspiration because the cortical tissue is attached more strongly to the capsule in the laser procedure. As experience with the laser-assisted procedure increases, the disparity between outcomes could increase. During our study, the more experienced surgeons no longer performed hydrodissection after the first few cases. Other surgeons found a reduction in hydrodissection, a more gentle approach to hydrodissection, or an adjustment to the technique to be beneficial to the procedure because the laser procedure generates gas and hence increases the volume in the capsular bag. Avoiding or minimizing hydrodissection should reduce the risk for anterior rupture, posterior capsule rupture, or capsular block syndrome (CBS), as reported by Roberts et al.,24 who concluded that an awareness of the changed intraocular environment created by the laser procedure and modification of the technique prevents CBS.

In addition to the adjustments to the phaco technique, one of the most important steps in performing femtosecond laser cataract surgery, regardless of the specific machine, is the docking process. With the Victus femtosecond laser, docking was found to be well centered and user friendly, with no corneal folds. We attribute this to the pressure sensors of the system. We observed the learning curve to be 5 to 10 cases once the surgeons became more familiar with using the patient interface and the docking process. In particular, centering and opening the capsulotomy with the femtosecond laser tended to improve with experience and then stabilize, providing a higher standard of accuracy and precision.

The safety profiles of the 2 procedures were equivalent. There were no adverse events, including posterior capsular tear, IOL malposition, iris damage, or retinal detachment, in either group at the 1-day follow-up. Our results compared favorably with findings in the literature.23,25 In our study, minor complications observed on the day of surgery included 2 incomplete capsulotomies in the femtosecond laser group, which we attribute to the learning curve for docking the patient interface. We also observed a much higher incidence of decentered capsulotomies and decentered IOLs in the manual group than in the laser group immediately postoperatively. We attribute this to the worse precision of the diameter and centration and reduced circularity of the capsulorhexis in the manual group. Initial visual inspection of IOL centration after surgery showed a higher level of nonconcentricity of the less precise capsulorhexis within the optic diameter in the manual group. However, this did not cause adverse events, and the 1-day postoperative safety evaluation found all IOLs to be centered with complete capsule overlap of the optic in both groups.

We found that the size, shape, and position of the anterior capsulotomy were significantly more predictable and accurate with the laser-assisted procedure than with the manual procedure. These results are consistent with those reported for other femtosecond lasers when used in both porcine and human eyes.2,7,26,27,D Palanker et al.2 reported a mean deviation of 27 ± 25 μm from the intended capsulotomy diameter using the laser versus −282 ± 305 μm with the manual technique and a mean circularity of 0.95 ± 0.04 compared with 0.77 ± 0.15. Friedman et al.26 also report a significant difference in the capsulotomy size and shape of the extracted capsule between a femtosecond laser and manual capsulorhexis, with a mean deviation from centration of 77 ± 47 μm in the laser group. Studies of stretch tests and tensile forces in porcine eyes using other femtosecond laser systems2,7,27 also found that the strength of the capsulotomy created with the laser was significantly stronger than the manually produced capsulotomy, which is in agreement with stretch-force measurements performed with the Victus system by Auffarth et al.28

Greater deviation in the accuracy of the capsulorhexis leads to greater postoperative asymmetric contractile forces on the IOL in the capsulorhexis, causing more IOL decentration.29 Although our study did not extend to measuring the visual impact of decentration, we realize the potential advantages of using the femtosecond laser technique to create more precise and reproducible capsulotomies and the possibility of improving refractive outcomes. Multifocal, accommodating, and toric IOLs, in particular, benefit from a well-formed circular and centered capsulotomy of a precise diameter because visual outcomes with these IOLs are more impaired by tilt and decentration.30–32 Nagy et al.33 observed that more regularly shaped femtosecond capsulotomies had improved centration and better IOL–capsule overlap than manual capsulorhexes. In their study comparing the effects on IOL centration of femtosecond laser capsulotomy and the manual technique, Kránitz et al.34 reported significantly higher values of overlap and circularity in the femtosecond group and significantly higher horizontal decentration in the manual group during the first year postoperatively. Furthermore, the study found that IOL decentration was 6 times more likely to occur in the manual group. Kránitz et al.35 also found that anterior capsulotomies created with the femtosecond laser resulted in less IOL decentration and tilt and better CDVA than the manual approach.

Our study has limitations. Four surgeons performed cases in the study, which introduced several variables, such as differing surgeon technique and experience, different phacoemulsification settings, and different fragmentation patterns. However, our study analyzed 2 groups with similar cataract grade distributions, and we believe our results are representative of introducing a femtosecond laser into a clinic where several surgeons are likely to use the system.

In conclusion, in the present study, the Victus femtosecond laser platform was effective and safe for lens fragmentation before phacoemulsification during cataract surgery. Its use reduced the EPT and average phaco energy and achieved precise and reproducible capsulotomies. Femtosecond laser cataract surgery is still in its relative infancy; thus, adjustments to technique are an inevitable part of adopting a new technology. Further evaluations are required to determine the optimum fragmentation patterns as a function of cataract grade and to assess the clinical significance of more accurate and centered capsulotomies and their effect on IOL positioning and visual and refractive outcomes.

What Was Known

  • Manual capsulorhexis (anterior capsulotomy) is considered the most difficult part of cataract surgery and is highly dependent on the skill of the individual surgeon.
  • Excess energy associated with standard phacoemulsification may cause capsule complications as well as damage to the corneal epithelium at the probe insertion site.
  • Femtosecond lasers, in general, can improve precision and reduce risks associated with cataract surgery.

What This Paper Adds

  • The femtosecond laser platform used was effective and safe for anterior capsulotomy and lens fragmentation before phacoemulsification during cataract surgery.
  • The use of this femtosecond laser platform significantly reduced the EPT and average phaco energy.
  • Anterior capsulotomy performed with the platform was significantly more predictable and accurate than that performed with the manual procedure.

References

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