Purpose
To compare the outcomes of phacoemulsification with toric intraocular lens implantation vs phacoemulsification with monofocal intraocular lens implantation followed by photorefractive keratectomy (PRK) for correction of pre-existing astigmatism.
Design
Randomized controlled trial, 6-month study.
Methods
setting : Institutional. study population : Sixty eyes of 52 patients with age-related senile cataract and regular corneal astigmatism ranging from 1.50 to 3.00 diopters, enrolled and randomly allocated in 2 groups based on computer-generated random number table. intervention : Group 1 patients underwent phacoemulsification with toric intraocular lens (IOL) implantation and Group 2 patients underwent phacoemulsification with monofocal IOL implantation followed by PRK 3 months later. main outcome measures : The main outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), residual cylinder, contrast sensitivity, glare acuity, pain score, and higher-order aberrations.
Results
At 6 months 53.3% of eyes in the toric IOL and 60% eyes in the monofocal IOL with PRK group attained UDVA of 20/20. Median residual refractive cylinder value was higher in the toric IOL group (toric IOL = −0.5, monofocal IOL with PRK = 0; P = .02). Mean root mean square value of total aberrations (5 mm pupil) was higher in monofocal IOL with PRK eyes (toric IOL= 1.02 ± 0.44, monofocal IOL with PRK = 1.28 ± 0.5; P = .04). Mean contrast sensitivity values were comparable. Mean toric IOL rotation was 1.3 ± 2.1 degrees. Mean glare acuity was better in toric IOL eyes (toric IOL = 0.46 ± 0.16, monofocal IOL with PRK = 0.73 ± 0.12; P < .001). Median postoperative pain scores were higher in monofocal IOL with PRK eyes.
Conclusion
PRK yields lesser residual cylinder compared to toric IOL. However, it causes greater postoperative pain and corneal aberrations, and poor glare acuity.
Astigmatism is a visually disabling refractive error that affects approximately 50% of the population older than 60 years of age. It has been seen that up to 22% of cataract surgery candidates have preexisting astigmatism exceeding 1.50 diopters (D). Various methods that have been described for managing preexisting corneal astigmatism include incisional refractive procedures (selective positioning of phacoemulsification incision, opposite clear corneal incisions, astigmatic keratotomy, limbal relaxing incisions, excimer laser–based procedures such as laser in situ keratomileusis and photorefractive keratectomy [PRK] and toric intraocular lens [IOL] implantation).
Incisional refractive procedures have limitations, such as the maximum amount of astigmatism that can be corrected, long-term mechanical instability, and the dependence of postoperative outcome on variables like age of the patient, number of incisions given, and the length and depth of incisions. Although excimer laser–based procedures overcome these drawbacks, they do not allow astigmatism correction at the time of cataract surgery. Astigmatism correction is done after the corneal wound has healed and refractive stability is achieved (2-stage procedure). Toric IOL implantation allows astigmatism correction at the time of cataract surgery (1-stage procedure). Several studies have found this method to be an effective option for astigmatism correction, but postoperative rotational stability remains an issue. This study aimed to compare the outcomes of phacoemulsification with toric intraocular lens implantation vs phacoemulsification with monofocal intraocular lens implantation followed by photorefractive keratectomy for astigmatism correction.
Methods
Study Design
This prospective randomized study included 60 eyes of 52 patients who presented in the outpatient department at Dr Rajendra Prasad Centre for ophthalmic sciences, All India Institute of Medical Sciences, New Delhi between 1st May 2012 and 28th February 2013. The study followed the tenets of the Declaration of Helsinki. Informed consent was obtained from the subjects after explaining of the nature and possible consequences of the study. The study was approved by the local institutional review board/ethics committee of All India Institute of Medical Sciences for all prospective cases (Ref. No. RT-25/04.05.2012). The study has been registered under Clinical Trials Registry–India, National Institute of Medical Statistics at Indian Council of Medical Research, New Delhi ( www.ctri.nic.in ) (REF/2013/11/005965).
Patient Selection
Inclusion criteria for patient selection were age-related senile cataract, regular corneal astigmatism ranging from 1.50 to 3.00 D, no ocular or systemic contraindications for surgery, and willingness to participate in the study. Exclusion criteria were astigmatism less than 1.50 D and greater than 3.00 D, corneal thickness less than 500 μm, complicated cataract, posterior segment pathology, irregular corneal astigmatism, systemic conditions (collagen vascular disease, immunosuppression, diabetes mellitus), and patients not willing or available for follow-up. Patients presenting in the outpatient department were randomly allocated into 1 of the 2 study groups. Patients enrolled in Group 1 underwent standard phacoemulsification with toric IOL implantation. Patients enrolled in Group 2 underwent standard phacoemulsification with monofocal IOL implantation followed by photorefractive keratectomy 3 months later. The personnel conducting the investigations were not aware of the study group to which the patient belonged.
Preoperative Evaluation
Preoperative examination included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), slit-lamp examination, intraocular pressure by Goldmann applanation tonometry, dilated fundus examination, manifest refraction, keratometry (Bausch and Lomb St Louis, Missouri, USA, manual keratometer), corneal topography (Oculus Pentacam HR Typ70900; Wetzlar, Germany), endothelial cell count (specular microscope, SP-3000P; Topcon, Europe), and tear film evaluation (Schirmer test, tear film break-up time). IOL power and axis determination for toric IOL was done using an online program available from the IOL manufacturer ( www.acrysoftoriccalculator.com ). Preoperative keratometry (flat and steep axis), surgeon’s preferred incision location, and the surgeon’s estimated surgically induced corneal astigmatism were used to determine the model and the axis of toric IOL placement. Spherical IOL power was determined by IOLMaster (IOLMaster 500, Zeiss Humphrey; Carl Zeiss Meditec AG, Jena, Germany) values. The targeted refraction was emmetropia.
Surgical Technique
All surgeries were done by the same surgeon under topical anesthesia. Group1 patients underwent phacoemulsification followed by toric IOL (foldable acrylic, Acrysof; Alcon, Fort Worth, Texas, USA) placement. Prior to surgery corneal marking was done at the 3-o’clock, 6-o’clock, and 9-o’clock position with the patient in an upright position using a bubble marker (ASICO; Duckworth & Kent, England). These reference points were used to mark the actual IOL placement axis in supine position using a Mendez ring (ASICO; Duckworth & Kent, England). A temporal clear corneal incision was made using a 2.75 mm keratome (slit knife; Alcon Laboratories, Inc, Fort Worth, Texas, USA) and viscoelastic (Healon, 1% sodium hyaluronate; Abbott Medical Optics, Uppsala, Sweden) was injected. Capsulorrhexis of diameter 5.0–5.50 mm was made to ensure an adequate overlap with the IOL optic. After phacoemulsification, the toric IOL was inserted in the capsular bag using a Monarch II injector (Alcon Laboratories, Inc, Fort Worth, Texas, USA). After complete removal of viscoelastic from the capsular bag was ensured, the IOL was aligned with the marked axis. The corneal wound was hydrated and no sutures were applied. Patients enrolled in Group 2 underwent standard phacoemulsification with a 2.75 mm clear corneal incision and a monofocal (foldable acrylic, Acrysof IQ) IOL was placed in the bag. Postoperatively, all patients received topical antibiotics and steroids for 6 weeks.
Three months later, patients with monofocal IOL underwent PRK. Topical antibiotics were started 3 days prior to the day of the scheduled procedure. Before the start of the procedure, topical 0.5% proparacaine hydrochloride (Paracaine; Sunways India Pvt Ltd, Mumbai, India) and 0.5% moxifloxacin hydrochloride (Vigamox; Alcon Laboratories, Inc, Fort Worth, Texas, USA) were instilled. Then, 20% alcohol was applied for 20 seconds using a well to loosen the corneal epithelium. The central 9.0 mm corneal epithelium was removed using a hockey knife. After centration was confirmed, excimer laser (WAVELIGHT EX-500 Excimer Laser; Alcon Surgicals, Fort Worth, Texas, USA) ablation was done involving the 6 mm central optic zone. A bandage contact lens was placed at the end of the procedure. Postoperatively, all patients received topical antibiotics, steroids, and preservative-free lubricants for 6 weeks.
Postoperative Follow-up
Patients were examined at 1 day, 3 days, 1 week, 1 month, 3 months, and 6 months postoperatively. UDVA, CDVA, manifest refraction, keratometry, corneal topography, pachymetry, endothelial cell count, pain score, and tear film were measured at each visit. Pain scores were evaluated using a standard subjective numerical pain scale ranging from 0 to 10 (11-point scale), where 0 indicates no pain and 10 indicates the worst imaginable pain. IOL axis measurement was done on the slit lamp. A thin coaxial slit was made and rotated until it overlapped with the axis marks on the IOL. The corresponding value on the slit lamp was noted and the difference between the actual IOL placement axis and the measured value was taken as the amount of rotation. Corneal haze was graded according to the grading system proposed by Fantes and associates. Surgically induced astigmatism was calculated using an online calculator (version 3.1; www.insighteyeclinic.in/SIA calculator.php ) using the preoperative and 1 month post–cataract surgery keratometry values (magnitude and axis), the site of incision (temporal), and the outer arc length of incision (2.75 mm). At 6 months, additional assessment included contrast sensitivity (Pelli-Robson contrast sensitivity test chart, Clement Clarke International Ltd, Harlow, Essex, England), glare acuity (Zeiss Humphrey Systems, Automatic Refractor Keratometer; Carl Zeiss Meditec, Dublin, California, USA), and aberrometry (Bausch & Lomb Zywave II aberrometer, Technolas Ophthalmolgische System, Feldkirchen, Germany).
Vector Analysis of Treatment
To determine the effectiveness of toric IOLs and PRK for astigmatism correction, vector analysis of astigmatism was done using the Alpins method. The 3 fundamental vectors studied were target induced astigmatism (TIA), surgically induced astigmatism (SIA), and difference vector (DV). The VectrAKt astigmatism analysis program was used to calculate all the variables. The refractive cylinder values at the spectacle plane were converted to the corneal plane for performing of all calculations. The following indices were calculated:
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Correction index: Calculated by dividing SIA by TIA. For the PRK group it compares preoperative and postoperative refraction; for the toric group it compares preoperative keratometry with postoperative refractive cylinder.
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Angle of error: The angle described by the vectors of SIA vs TIA.
The primary outcome measure was the amount of residual cylinder. The secondary outcome measures were UDVA, CDVA, contrast sensitivity, glare acuity, pain score, and higher-order aberrations (HOA).
Statistical Analysis
A sample size of 30 for each group was calculated considering 80% power of the study, 5% level of significance, and 20% loss during follow-up. Patients fulfilling the inclusion criteria were randomized at their first visit. Sixty eyes of 52 patients were included in the study. If both eyes were treated, the eyes were then separately evaluated. The eyes were randomized based on a computer-generated random number table. No masking was done. The analysis was done according to the group to which the patients were originally assigned. Results were analyzed at 6 months. Mean values, standard deviations, and frequency (%) distributions were calculated for each parameter. Intergroup comparisons were done using t test and its nonparametric analog Wilcoxon rank sum test. Within-group comparisons (between preoperative and postoperative visits and between consecutive postoperative visits) were done using repeated-measure analysis of variance and its nonparametric analog Friedman test (for an overall comparison) and Wilcoxon signed rank test with Bonferroni correction (for multiple comparisons). Results were considered statistically significant if P value was less than .05.
Results
The toric IOL group included 30 eyes of 25 patients and the PRK group included 30 eyes of 27 patients. The baseline characteristics such as age, sex distribution, keratometry, and keratometric cylinder were comparable among the 2 groups ( Table 1 ).
| Variables | Toric IOL | Monofocal IOL With PRK | P Value |
|---|---|---|---|
| Age (y) | 58.55 ± 15.3 | 63.4 ± 7.3 | .12 |
| Sex distribution | M = 67%, F = 33% | M = 80%, F = 20% | .24 |
| Mean Km (D) | 43.65 ± 1.39 | 44.20 ± 0.85 | .06 |
| Mean Km cylinder(D) | 2.427 ± 0.56 | 2.11 ± 0.63 | .10 |
Refractive Outcome
The median refractive cylinder values at 1 month and at 3 months were comparable between the 2 groups, but at 6 months the difference was statistically significant ( P = .02; Table 2 ). A total of 86.6% (26/30) of toric IOL eyes attained residual refractive cylinder less than 0.5 D while among PRK eyes this value was 96.6% (29/30) at 6 months. None of the patients in either of the 2 groups had residual cylinder more than 0.75 D. The median spherical equivalent value was comparable among the 2 groups at all follow-up visits. At 6 months 86.6% (26/30) of toric IOL eyes and 93.3% (28/30) of PRK eyes had spherical equivalent value less than 0.5 D.
| Variables | Toric IOL | Monofocal IOL With PRK | P Value |
|---|---|---|---|
| UDVA, median (min, max) | 0 (0, 0.3) | 0 (0, 0.18) | .7177 |
| CDVA, median (min, max) | 0 (0, 0.18) | 0 (0, 0.18) | .6901 |
| Refractive cylinder (D), median (min, max) | −0.5 (0, −0.5) | 0 (0, −0.75) | .0205 |
| SEQ, median (min, max) | 0 (0.5, −1.25) | 0 (0.5, −0.75) | .8673 |
| Contrast sensitivity, mean ± SD | 1.59 ± 0.055 | 1.58 ± 0.061 | .5115 |
| Glare acuity, mean ± SD | 0.462 ± 0.164 | 0.736 ± 0.120 | <.001 |
| Total aberrations (5 mm zone), mean ± SD | 1.021 ± 0.446 | 1.28 ± 0.516 | .0413 |
| Total aberrations (6 mm zone), median (min, max) | 1.275 (0.49, 4.36) | 1.82 (0.8, 4.69) | .0183 |
| HOA (5 mm zone), median (min, max) | 0.395 (0.12, 1.8) | 0.63 (0.2, 1.19) | .0001 |
| HOA (6 mm zone), median (min, max) | 0.65 (0.33, 3.25) | 0.9 (0.46, 2.58) | .0014 |
Visual Functions
The median UDVA and CDVA value were comparable among the 2 groups at all follow-up visits. UDVA equal to or better than 20/20 (6/6) was seen in 53.3% (16/30) of toric IOL eyes and 60% (18/30) of PRK eyes at 6 months postoperatively.
The mean log contrast sensitivity values at 6 months were comparable among the 2 groups ( P = .51; Table 2 ). The mean glare acuity value at 6 months was better in toric IOL eyes ( P < .001; Table 2 ).
The mean and median root mean square (rms) values of total and higher-order aberrations at 5 mm and 6 mm pupil zone were significantly higher in PRK eyes at 6 months postoperatively. The corresponding rms values in toric IOL eyes were within the acceptable normal range (total aberrations: 5 mm pupil, P = .04; 6 mm pupil, P = .01; HOA: 5 mm pupil, P = .0001, 6 mm pupil, P = .001) ( Table 2 ).
Comparison of the 2 groups after cataract surgery revealed comparable contrast sensitivity ( P = .284) and total ( P = .122) as well as higher-order aberrations ( P = .440), but better glare acuity ( P = .013) in the monofocal IOL group ( Table 3 ).
| Variables | Toric IOL | Monofocal IOL (Pre-PRK) | P Value |
|---|---|---|---|
| Contrast sensitivity, mean ± SD | 1.59 ± 0.05 | 1.58 ± 0.05 | .284 |
| Glare acuity, mean ± SD | 0.46 ± 0.16 | 0.56 ± 0.14 | .013 |
| Total aberrations (5 mm zone), mean ± SD | 1.02 ± 0.44 | 1.24 ± 0.65 | .122 |
| Total aberrations (6 mm zone), mean ± SD | 1.50 ± 0.84 | 1.93 ± 0.94 | .070 |
| HOA (5 mm zone), mean ± SD | 0.46 ± 0.30 | 0.51 ± 0.24 | .440 |
| HOA (6 mm zone), mean ± SD | 0.77 ± 0.53 | 0.85 ± 0.53 | .559 |
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