Tzahi Sela

Risk factors for keratoconus in Israel: a case–control study

Keratoconus (KC) is a progressive corneal thinning disorder with an uncertain aetiology. Environmental and genetic factors, including consanguinity, eye rubbing and possibly sun exposure, play a role in the aetiology of KC. Here we test for risk factors for KC in an Israeli population with particular emphasis on sun exposure.

Factors Predicting the Need for Retreatment After Laser Refractive Surgery.

Purpose: To identify the potential risk factors that increase the likelihood of requiring retreatment after refractive surgery. Methods: This retrospective study included patients who underwent laser in situ keratomileusis or photorefractive keratectomy between January 2005 and December 2012 at the Care-Vision Laser Centers, Tel-Aviv, Israel. Patients were divided into 2 groups according to whether they underwent additional refractive surgery (retreatment) during the study period. Results: Overall, 41,504 eyes (n = 21,313) were included in the final analysis of this study. Throughout the study period, there was a significant reduction in the 2-year annual retreatment rates with a decline from 4.52% for primary surgeries done in 2005 to 0.18% for surgeries performed in 2012 (quadratic R2 = 0.96, P < 0.001). The retreatment group had significantly higher preoperative age, maximum keratometric power, sphere, cylinder, and better best-corrected visual acuity. They were more likely to have preoperative hyperopia, photorefractive keratectomy as opposed to laser in situ keratomileusis, intraoperative higher humidity conditions and lower temperature, and higher ablation depths. Significant differences in retreatment rates were found between the 5 high-volume surgeons (>1500 procedures performed) ranging from 0.48 to 3.14% (P < 0.0001). Multiple logistic regression analysis demonstrated that age, astigmatism, hyperopia, temperature, and surgeons experience all significantly affected the need for retreatment. Conclusions: The following factors significantly increase the need for refractive retreatment: older preoperative age, higher degrees of astigmatism, hyperopia, colder operating room temperature, and less surgeon experience. Some of these factors may be incorporated into nomograms to reduce future retreatment rates.

Comparison of Three Epithelial Removal Techniques in PRK: Mechanical, Alcohol-assisted, and Transepithelial Laser.

PURPOSE To compare the visual and refractive results obtained after photorefractive keratectomy (PRK) in patients who underwent one of three different epithelial removal techniques. METHODS The authors reviewed the medical files of consecutive eyes with myopia and myopic astigmatism that were treated during a 10-year period by mechanical PRK, alcohol-assisted PRK, or transepithelial PRK (in the phototherapeutic keratectomy mode), and observed for more than 1 year. RESULTS A total of 3,417 patients (3,417 eyes) were included in this study. At 3 and 6 months postoperatively, the outcome of alcohol-assisted PRK was superior both in efficacy (P < .01) and safety (P < .001) to those of both mechanical PRK and transepithelial PRK, which were similar. At more than 1 year postoperatively, the mean efficacy index was still high for alcohol-assisted PRK, but low for the transepithelial PRK, corresponding to a mean uncorrected visual acuity of more than one Snellen line lower than those of the other two techniques (P < .0001). All three techniques showed a regression toward myopia more than 1 year postoperatively, with significant undercorrection obtained in eyes treated with transepithelial PRK (P < .0001). CONCLUSIONS Significant differences were detected in both the visual outcomes and the refractive results of the three epithelial removal techniques. The long-term outcomes were best for alcohol-assisted PRK.

Myopic laser in situ keratomileusis retreatment: Incidence and associations

Purpose To determine the factors associated with retreatment after laser in situ keratomileusis (LASIK) for myopic eyes in the modern LASIK era. Setting Care‐Vision Laser Centers, Tel‐Aviv, Israel. Design Retrospective cohort study. Methods All cases of myopic LASIK performed between January 2005 and December 2012 were analyzed according to whether they had retreatment refractive surgery. Result The study evaluated 9177 right eyes in 9177 consecutive LASIK cases. The mean preoperative subjective spherical equivalent and astigmatism were −3.30 diopters (D) ± 1.53 (SD) (range −0.50 to −12.00 D) and 0.69 ± 0.94 D (range 0.00 to 6.00 D), respectively. Of the eyes, 165 (1.80%) had at least 1 retreatment. Over the course of the study, the 2‐year retreatment rate decreased from 2.58% to 0.38% (P < .001). Multiple binary logistic regression analysis showed that older age (odds ratio [OR], 1.03; P = .007), higher astigmatism (OR, 1.23; P = .008), sphere (OR, 1.15; P = .026), and mean keratometric power (OR, 1.13; P = .036) significantly increased the odds for retreatment. A larger optical zone ablation (7.0 mm) significantly decreased the odds for retreatment (OR, 0.10; P = .022). Significant cutoffs associated with retreatments were age greater than 50 years, astigmatism more than 1.5 D, and sphere more than 2.0 D. Conclusions Older age and higher preoperative astigmatism, sphere, and corneal steepness were associated with myopic LASIK retreatment. Larger optical ablation zones might decrease retreatment rates. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

The Effect of Astigmatism Axis on Visual Acuity

Purpose To evaluate the effect of astigmatism axis on uncorrected distance visual acuity (UDVA) in emmetropic eyes that underwent laser refractive surgery. Methods This retrospective study included patients who underwent laser in situ keratomileusis or photorefractive keratectomy between January 2000 and December 2015 at the Care-Vision Laser Centers, Tel Aviv, Israel. Eyes with a 3-month postoperative spherical equivalent between -0.5 D and 0.5 D were included in this study. Eyes with ocular comorbidities and planned ametropia were excluded. Study eyes were divided into 3 groups according to the steep astigmatic axis: with the rule (WTR) (60-120), oblique (31-59 or 121-149), and against the rule (ATR) (0-30 or 150-180). The UDVA of these 3 groups was compared. The oblique group was divided into oblique ATR and oblique WTR, which were compared with each other. Results A total of 17,416 consecutive eyes of 8,708 patients were studied. The WTR eyes (n = 10,651) had significantly better UDVA (logMAR 0.01 ± 0.08) than the oblique (n = 3,141, logMAR 0.02 ± 0.09) and ATR eyes (n = 3,624, logMAR 0.02 ± 0.10) (p<0.001). The oblique WTR group had significantly better UDVA than the oblique ATR group (p<0.001). The UDVA of the oblique and ATR groups was similar. Stepwise multiple regression analysis showed that the group accounted for 15% of the UDVA variance (p = 0.04). Conclusions The astigmatic axis has a small but significant effect on UDVA in emmetropic eyes; WTR was better than oblique and ATR astigmatism. Therefore, when correcting astigmatism, it may be preferable to err towards WTR astigmatism.

Visual acuity outcomes in eyes with flat corneas after PRK.

PURPOSE To evaluate the impact of corneal curvatures less than 35 diopters (D) after photorefractive keratectomy (PRK) on visual acuity outcomes. METHODS Visual acuity outcomes of 5,410 eyes that underwent PRK from January 2006 to November 2010 were retrospectively analyzed for the impact of postoperative corneal curvatures on visual outcomes. All procedures were performed on a single platform (Allegretto 200Hz excimer laser; Alcon Laboratories, Inc., Irvine, CA). Main outcome measures were postoperative corrected distance visual acuity (CDVA) and loss of CDVA. RESULTS Corneas with a measured or a calculated postoperative flat meridian less than 35 D and those with a measured postoperative steep meridian less than 35 D had worse postoperative CDVA than corneas with meridians of either 35 D or more (P ≤ .021). However, the preoperative CDVA was worse in the flatter curvatures in all comparisons performed (P ≤ .024). Consequently, the measured or calculated meridian curvature had no effect on CDVA loss (P ≥ .074). CONCLUSION Postoperative corneal keratometry values (flat and steep meridians) less than 35 D did not have a predictive effect on the risk of losing visual acuity following myopic PRK performed on the Allegretto 200Hz excimer laser.

Corneal Breakthrough Haze After Photorefractive Keratectomy With Mitomycin C: Incidence and Risk Factors

Purpose: To identify preoperative and intraoperative factors affecting breakthrough corneal haze incidence after photorefractive keratectomy (PRK) with mitomycin C (MMC). Methods: In this retrospective study of PRK performed at the Care Vision Refractive Laser Center, Tel Aviv, Israel, a total of 7535 eyes (n = 3854 patients; mean age ± SD, 26 ± 6 years; 55% men) underwent PRK with intraoperative MMC application. Patients with histories of corneal pathology or surgery were excluded. Incidence, time of onset, and corneal haze severity were documented on follow-up of 118 ± 110 days. Eyes were grouped by preoperative refraction [low (⩽−3D), moderate (−3D to −6D), or high (>−6D) myopia; low (⩽3D) or high (>3D) astigmatism; low or high hyperopia]; by intraoperative time (above or below 40 seconds); and by MMC application time (above or below 40 seconds). The main outcome measures were incidence, onset time, and severity of corneal haze. Results: The haze incidence was 2.1% in eyes with high myopia versus 1.1% in those with low to moderate myopia (P = 0.002), and 3.5 times higher in eyes with high than with low astigmatism (P < 0.05). The overall incidence was higher in eyes treated for hyperopia (10.8%) than for myopia (1.3%) (P = 0.0001). In eyes with moderate myopia, the haze incidence was lower in MMC application time ≥40 seconds (0%) than in <40 seconds (1.3%) (P = 0.03). After surgery, a mild early haze incidence peaked at 68.8 ± 6 days and severe late haze at 115 ± 17 days (P = 0.02). Conclusions: Hyperopic and large myopic or astigmatic corrections carry higher risk of haze. Longer MMC application might have beneficial haze prevention.

Effect of Anisometropia on the Predictability and Accuracy of Refractive Surgery.

Purpose: To evaluate the predictability and accuracy of refractive surgery among adults with myopic anisometropia. Methods: Consecutive cases of myopic eyes that underwent bilateral laser-assisted in situ keratomileusis (LASIK) or bilateral photorefractive keratectomy (PRK) during a 12-year period in a single center were included. Myopic anisometropia was defined as a difference greater than 1.5 D in spherical equivalent between eyes preoperative. Results: A total of 10,046 paired, operated nonamblyopic eyes of 5023 patients were analyzed. Of these, 472 eyes of 236 (4.7%) patients had myopic anisometropia without amblyopia, and 9574 eyes of 4787 patients served as isometropic controls. After refractive surgery, in the anisometropic group the more myopic eye was corrected by +0.47 ± 0.78 (D) more than the contralateral eye (P < 0.0001). Relative to the target refraction, the more myopic eye was overcorrected by 0.21 ± 0.79 D compared with an undercorrection of 0.16 ± 0.60 D in the less myopic contralateral eye (P < 0.0001) and compared with an undercorrection of 0.15 ± 0.62 D in the isometropic controls (P < 0.0001). Additionally, the variability in the correction of the more myopic eyes was significantly higher compared with the less myopic contralateral eyes and isometropic controls (P < 0.0001). These trends were evident both in PRK and LASIK treatments. The effect of anisometropia was found to be independent of the magnitude of preoperative myopia or surgeon identity. Conclusions: The more myopic eye of anisometropes undergoing refractive surgery has lower predictability and accuracy and tends to be overcorrected, whereas the less myopic eye has outcome similar to isometropic controls. These results suggest that refractive surgery nomograms should take into account anisometropia.

Factors affecting laser in situ keratomileusis flap thickness: Comparison of 2 microkeratome heads

Purpose To identify the potential factors affect that affect the thickness of corneal flaps created using 2 different microkeratome heads. Setting Care‐Vision Laser Centers, Tel‐Aviv, Israel. Design Retrospective comparative study. Methods The study included eyes in which bilateral laser in situ keratomileusis (LASIK) was performed from January 1, 2005, to December 31, 2012, using an SBK‐90 microkeratome head (Group 1) or an M2‐90 microkeratome head (Group 2). Inclusion criteria were at least 18 years of age, a stable refraction for 12 months, an intraocular pressure of less than 21 mm Hg, and no history of autoimmune disease, diabetes, ocular surgery, or eye disease. In addition, patients had to cease wearing contact lenses for 2 weeks (rigid lenses) or 4 days (soft lenses) before the preoperative evaluation and before surgery. The disposable blade was used in the right eye first and then reused in the left eye. Results The study evaluated 6242 eyes of 3121 patients with a mean age of 32.2 years ± 9.8 (SD). Group 1 comprised 2560 eyes (41%), and Group 2 comprised 3682 eyes (59%). The eyes in Group 1 had thinner flaps (P < .001). The right eyes had thicker flaps (P < .001). Flap thickness had a positive correlation with precutting central corneal thickness (CCT) and operating room humidity and a negative correlation with patient age, preoperative sphere and cylinder, and operating room temperature. Statistically significant differences were found in flap thickness between surgeons (P < .001). Larger suction rings created thicker flaps (P < .001). Stepwise regression models accounted for up to 28.1% of the variation in flap thickness. Conclusions Factors that were significantly correlated with flap thickness included the precutting CCT, whether the right or the left eye, the microkeratome head used, the surgeon performing the procedure, and the preoperative sphere. These findings might help prevent post‐LASIK corneal ectasia. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Risk Factors for Re-treatment Following Hyperopic LASIK

PURPOSE To determine the risk factors for re-treatment following LASIK in hyperopic eyes. METHODS In this retrospective study, consecutive hyperopic eyes underwent LASIK at the Care Vision Laser Centers, Tel-Aviv, Israel, between January 2000 and October 2014. Patients were divided into two groups according to whether or not they underwent additional refractive surgery (re-treatment). Logistic regression was performed to determine predictors of re-treatment. RESULTS Overall, 1,776 eyes of 888 patients were included, of which 82 (4.6%) needed re-treatment. Eyes that underwent re-treatment were of older age (49.1 ± 7.5 vs 46.9 ± 10.3 years, P = .01), had better preoperative CDVA (1.0 ± 0.14 vs 0.95 ± 0.15 decimal, P = .001), were treated more often with the Allegretto EX200 (Alcon Laboratories, Inc., Fort Worth, TX) as opposed to the EX-500 (90.2% vs 63.7%, P < .001), and were treated with a Moria M2-90 microkeratome (Moria S.A., Antony, France) as opposed to Moria SBK-90 (66.7% vs 36.4%, P < .001). Multiple logistic regresison analysis demonstrated that treatment with Allegretto EX200 (odds ratio: 2.67, P = .04), and Moria M2-90 microkeratome (odds ratio: 2.23, P = .04) and older age (odds ratio: 1.03, P = .03) were significant risk factors for re-treatment. CONCLUSIONS Factors associated with a higher risk of re-treatment following hyperopic LASIK include type of laser, type of microkeratome used, and older age. Identifying such factors may aid in reducing future retreatment rates in hyperopic LASIK. [J Refract Surg. 2018;34(5):316-320.].