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Toric intraocular lens implantation versus astigmatic keratotomy to correct astigmatism during phacoemulsification

Titiyal, Jeewan S. MD; Khatik, Mukesh MD; Sharma, Namrata MD*; Sehra, Sri Vatsa MD; Maharana, Parfulla K. MD; Ghatak, Urmimala MD; Agarwal, Tushar MD; Khokhar, Sudarshan MD; Chawla, Bhavana MS

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Journal of Cataract & Refractive Surgery: May 2014 - Volume 40 - Issue 5 - p 741-747
doi: 10.1016/j.jcrs.2013.10.036
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Abstract

There has been a paradigm shift in patient and surgeon expectations of cataract surgery. The procedure is no longer just a means to restore visual acuity but is also a way to achieve emmetropia in many cases. However, a significant obstacle is astigmatism, with 15% to 56% of eyes having greater than 1.00 diopter (D) of astigmatism after phacoemulsification.1 Astigmatism produces glare, monocular diplopia, asthenopia, and visual distortion. Preexisting astigmatism during cataract surgery may be corrected by modifying the incision,1,2 creating limbal relaxing incisions (LRIs),1,3 performing astigmatic keratotomy (AK),1,3–8 and, more recently, implanting a toric intraocular lens (IOL).9–19

Astigmatic keratotomy and toric IOL implantation are important procedures to correct moderate to severe astigmatism. Although several studies have evaluated these separately, a comparative evaluation has not been reported. In this study, we compared the results of toric IOL implantation with those of AK in patients with moderate regular astigmatism who had phacoemulsification.

Patients and methods

This prospective randomized clinical trial was approved by the institutional review board at the tertiary care referral center. The tenets of the Declaration of Helsinki were followed.

Consecutive patients from 45 to 65 years old who presented to the outpatient department or anterior segment services of the center with visually significant immature senile cataract, regular bow-tie moderate corneal astigmatism (1.25 to 3.0 D), and no ocular or systemic contraindications to surgery were included. Patients with complicated cataract, posterior segment pathology, astigmatism less than 1.25 D or greater than 3.00 D, or a systemic condition likely to result in an unpredictable response to surgery (eg, collagen vascular disease, diabetes mellitus) were excluded. Also excluded were patients who expressed an inability to attend follow-up visits or who were not willing to provide written consent.

Patients who met the inclusion criteria were recruited and randomized into 2 groups with an equal number of eyes. Randomization was performed using a table of random numbers.

All patients had clear corneal temporal phacoemulsification surgery. This was followed by implantation of a foldable toric IOL (Acrysof IQ Toric, Alcon Surgical, Inc.) in the toric IOL group and by AK with implantation of a foldable aspheric IOL (Acrysof IQ, Alcon Surgical, Inc.) in the keratotomy group.

Preoperatively, patients had an extensive ophthalmologic evaluation including uncorrected distance visual activity (UDVA), corrected distance visual acuity (CDVA), cycloplegic refraction with homatropine 2.0%, slitlamp biomicroscopy, clinical photography, videokeratography (Atlas 9000, Carl Zeiss Meditec AG), scanning-slit topography (Orbscan II, Bausch & Lomb), noncontact specular microscopy (Topcon SP 3000 P), manual keratometry (Bausch & Lomb), and ultrasound pachymetry (Micropach Model 200P+, Sonomed, Inc.) to measure central corneal thickness (CCT).

Surgical Technique

Phacoemulsification surgery was performed using topical anesthesia (proparacaine hydrochloride 0.5%). The same surgeon (J.S.T.) performed all surgeries.

In the toric IOL group, a preoperative reference mark was placed with a marking pen at the 6 o’clock limbus and at 3 o’clock and 9 o’clock under slitlamp biomicroscopy. The final orientation of the steep meridian was confirmed against this marking on the operating table using an axis-marking dial on the table. A self-sealing temporal clear corneal incision was created with a 2.75 mm keratome, and phacoemulsification was performed. The IOL was implanted in the capsular bag using a Monarch II injector with a C-cartridge (Alcon Laboratories, Inc.). Initially, the IOL was rotated into a position that was approximately 15 degrees short of the actual marked axis of placement. The residual ophthalmic viscosurgical device was removed from behind the IOL and from the anterior chamber. Subsequently, the IOL was rotated to align the peripheral dots on it with the marked steep meridian on the cornea. The anterior chamber was reformed, and stromal hydration of the main incisions and paracentesis was performed. Correct alignment of the IOL was again verified at the end of surgery. All incisions were hydrated and left sutureless after they were checked for leakage.

In the keratotomy group, preoperative reference marks were placed at 6 o’clock, 3 o’clock, and 9 o’clock at the limbus under slitlamp biomicroscopy, as in the toric IOL group. Astigmatic keratotomy was performed before phacoemulsification.20 The center of the cornea and a 7.0 mm optical zone were marked. A 12-blade radial keratotomy marker was placed on the 7.0 mm optical zone mark. Paired arcuate keratotomy incisions were made in the 7.0 mm optical zone. The 30-degree paired AK cuts were made on the steeper meridian using a micrometer-guided diamond knife (Meyco) that was set at 100% of the thinnest paracentral pachymetry. Next, a 2.75 mm clear corneal temporal incision was created, phacoemulsification was performed, and a foldable IOL was implanted. The wound was hydrated at the end of surgery and left sutureless after it was checked for leakage.

Postoperatively, patients were advised to avoid trauma to their operated eye. They were prescribed topical moxifloxacin hydrochloride 0.5% 4 times a day for 4 weeks; prednisolone acetate 1.0% 4 times a day for 4 weeks, after which it was tapered; and tropicamide 1.0% 2 times a day for 3 weeks.

Outcome Measures

Patients were examined 1 day, 1 week, and 1 and 3 months after surgery. The UDVA and CDVA were assessed using a standard wall-mounted Snellen chart. Slitlamp biomicroscopy was performed to assess the anterior segment. Corneal topography was evaluated using videokeratography and scanning-slit topography. The endothelial cell density (ECD) was calculated using noncontact specular microscopy. Subjective refraction and manual keratometry were performed, and the residual astigmatism (vector analysis using the postoperative subjective refraction) was calculated. The toric IOL axis was determined under mydriasis using the degree scale on the vertical arm of the slitlamp. Photographs were taken at each follow-up to compare the slitlamp axis estimates with those obtained using Adobe Photoshop CS2 image-editing software (version 9.0.2, Adobe Systems, Inc.).21

Statistical Analysis

Statistical analysis was performed using SPSS for Windows software (version 16.0, SPSS, Inc.). The sample size was calculated as a minimum of 15 eyes in each group to attain a power of 0.8 and an α of 0.05. Visual acuity was converted from Snellen fraction notation to the logMAR scale for analysis. For description, quantitative variables were expressed as the mean ± standard deviation and qualitative variables as a percentage. The chi-square test was used for categorical variables. The Mann-Whitney and Wilcoxon signed-rank tests were used for quantitative variables. Comparison between groups was performed using independent t tests. A P value less than 0.05 was considered statistically significant.

Results

The study enrolled 34 eyes of 34 patients; each of the 2 groups comprised 17 eyes. There were no dropouts in either group, and all patients were followed regularly for a minimum of 3 months. Table 1 compares the baseline parameters between the toric IOL group and the keratotomy group; the groups were comparable in all parameters.

Table 1
Table 1:
Comparison of baseline parameters between the toric IOL group and the keratotomy group.

Visual Acuity

Postoperatively, vision improved in both groups (Figure 1). There was no statistically significant difference in UDVA or CDVA between the groups at any time during the follow-up. After 3 months, the mean UDVA was 0.15 ± 0.01 logMAR in the toric IOL group and 0.21 ± 0.11 logMAR in the keratotomy group (P=.24). The CDVA was 0.00 logMAR in all patients in both groups at the 3-month follow-up (P=.99).

Figure 1
Figure 1:
Uncorrected distance visual acuity (UDVA) over the follow-up. The length of the vertical line depicts the standard deviation (IOL = intraocular lens).

Refraction

Refractive astigmatism decreased in both groups. There was no statistically significant difference between the 2 groups at any follow-up (Table 2). All eyes in the toric IOL group and 14 eyes (84%) in the keratotomy group had residual astigmatism of 1.00 D or less. Three eyes in the keratotomy group had residual astigmatism of 1.50 D or less (P=.17) (Figure 2).

Figure 2
Figure 2:
Postoperative residual refractive astigmatism (IOL = intraocular lens).
Table 2
Table 2:
Change in astigmatism over time by group.
Table 2
Table 2:
Continued.

Keratometry

There was a postoperative reduction in corneal astigmatism in the keratotomy group but no significant change in the toric IOL group (Table 2).

Residual Astigmatism

Vector analysis of subjective refraction showed that at 3 months, the residual astigmatism was 0.44 ± 1.89 @ 160 and 0.77 ± 1.92 @ 174 in the toric IOL group and keratotomy group, respectively (P=.61). There was no statistically significant difference between the groups at any follow-up (Table 3).

Table 3
Table 3:
Residual astigmatism by group.

Specular Microscopy

Both groups had a statistically significant reduction in ECD after surgery, which was evident at 1 day of follow-up (both P=.01). Endothelial cell density did not change significantly after that time. By the end of 3 months, the mean percentage decrease was 1.7% in the toric IOL group and 3.0% in the keratotomy group. There was no statistically significant difference between the groups at any follow-up.

Complications

The IOL alignment in the toric IOL group was within the acceptable range. The mean misalignment was 4.8 ± 1.2 degrees. No IOL was misaligned more than 10 degrees. Potential complications of AK, such as corneal ectasia or a hyperopic shift, were not seen in any eye. There was no statistically significant regression of the astigmatic correction in either group postoperatively.

Discussion

Astigmatism in eyes having cataract surgery can be managed by surgical methods including LRIs, AK, and toric IOL implantation. Astigmatic keratotomy has been extensively studied as a means to reduce corneal astigmatism; guidelines for this procedure were formulated by the Prospective Evaluation of Astigmatic Keratotomy Study and the Astigmatism Reduction Clinical Trials (ARC-T) group.22–24 Astigmatic keratotomy has shown good results in reducing astigmatism in patients having cataract surgery.24,25 Toric IOL implantation is a newer modality for the correction of astigmatism in patients having cataract surgery. Since the first report by Shimizu et al. in 1994,9 several studies6,11–13,15–19,26–31 have evaluated results of toric IOL implantation in these patients. Poll et al.32 compared toric IOL implantation with peripheral corneal relaxing incisions in 2011. They found that the 2 modalities were comparable in cases of mild to moderate astigmatism, while toric IOL implantation may be a better option in eyes with a higher degree of astigmatism.

To our knowledge, no previous study compared the outcomes of toric IOL implantation with those of AK in patients having phacoemulsification. In our study, the 2 procedures gave comparable results. At all follow-up visits, the visual acuity and mean astigmatism were comparable in the toric IOL group and the AK group. The corneal cylinder was higher than the refractive cylinder in the AK group at the 6-month follow-up. This may be different at 1 year because the AK incisions take time to heal. A subanalysis of these cases by separating them into groups of with-the-rule astigmatism and against-the-rule astigmatism was attempted but did not yield meaningful results due to the small numbers. We did not make adjustments to the nomogram, and this may have contributed to less than optimum results. Also, there may be an element of posterior corneal astigmatism; this has been reported recently33 and may decrease the accuracy of the procedure; we did not take this into account. No regression of astigmatic correction was noted in either group.

Toric IOL implantation has inherent advantages over AK. It is less surgically demanding and does not require the use of special instruments; it also does not increase the duration of the phacoemulsification surgery. Furthermore, there are reports of microbial keratitis,34 endophthalmitis,34 cystoid macular edema,35 retinal detachment,36 and epithelial ingrowth after AK.37 Although there were no cases of regression of astigmatic correction after AK in our study, results may be unpredictable, as reported by the ARC-T study group.38 The possibility of corneal ectasia after AK should also be kept in mind, in particular in patients with thin corneas.39

A possible concern with toric IOL implantation is rotational stability19,29; however, in our study, toric IOL alignment was maintained within 10 degrees of the intended axis and no IOL required surgical repositioning. Another drawback is the additional cost of toric IOLs.

To conclude, in our study, both procedures—cataract surgery with toric IOL implantation and cataract surgery with AK—were comparable in terms of postoperative astigmatism and visual acuity in eyes with moderate astigmatism. Either procedure may be used to correct astigmatism in this range.

What Was Known

  • Toric IOL implantation and AK are effective procedures to treat astigmatism during cataract surgery. Although toric IOLs are expensive, AK is a specialized procedure that requires additional surgical skills.
  • Although the techniques have been studied individually, it is not known how they compare with each other and which procedure should be preferred.

What This Paper Adds

  • Toric IOL implantation and AK gave comparable visual and astigmatic results.
  • The results indicate that either procedure can be used to treat astigmatism during cataract surgery. The choice of procedure can be made based on patient and surgeon preference.

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