Factors associated with changes in posterior corneal surface following laser-assisted in situ keratomileusis.

PURPOSE: To identify factors associated with changes in the posterior corneal curvature following laser-assisted in situ keratomileusis (LASIK). METHODS: This retrospective study included myopic astigmatic eyes that underwent LASIK between January and December 2013 at Care-Vision Laser Center, Tel-Aviv, Israel. The average posterior keratometry was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgically induced change in average posterior keratometry and preoperative parameters such as preoperative sphere, cylinder, spherical equivalent, central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci (BCV) index, ablation depth, percent of tissue altered (PTA), and residual stromal bed (RSB) are reported. RESULTS: A total of 115 eyes with a mean age of 32.5 ± 8.3 years (range 22-56 years) were included. Central corneal thickness (p < 0.005), preoperative sphere (p < 0.001), spherical equivalent (p < 0.005), and preoperative posterior inferior/superior ratio (p < 0.05) were all significantly correlated with the percentage of change in the mean posterior K. According to ranked stepwise multiple regression analysis, 22% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were the percentage of change in posterior inferior/superior ratio, preoperative subjective sphere, and preoperative mean posterior K (for all, p < 0.001). CONCLUSIONS: The percentage of change in posterior inferior/superior ratio, subjective sphere, and preoperative mean posterior K are all correlated with change in the mean posterior K after LASIK. Understanding of the variables that can influence posterior corneal changes following refractive surgery may play a role in the prevention of iatrogenic keratectasia.

Myopia and myopic astigmatism photorefractive keratectomy: applying an advanced multiple regression-derived nomogram.

PURPOSE: To evaluate a multiple regression-derived nomogram for myopia and myopic astigmatism photorefractive keratectomy (PRK). METHODS: Regression modeling derived a formula for spherocylindrical correction in wavefront-optimized PRK (nomogram II). Treatment outcomes between eyes with myopia and myopic astigmatism using the manufacturer's nomogram (nomogram I) in the years 2010-2013 were retrospectively compared with eyes treated using nomogram II in the years 2014-2015. RESULTS: Overall 1100 eyes (of 561 patients) were operated using nomogram I and 791 eyes (of 406 patients) using nomogram II. Nomogram II achieved correction within ± 0.5 D of the attempted in 90% (95% CI 86.8-92.3%) of eyes with a spherical equivalent (SE) < |- 6|D, compared to 84% (95% CI 81.8-86.9%) in nomogram I. Overcorrection was reached in 14% (95% CI 10.1-18.3%) of eyes with SE ≥ |-6|D in nomogram II, compared to 22.6% (95% CI 18.1-27.2%) in nomogram I. Nomogram II achieved correction within ± 0.5 D of the attempted in 88.7% (95% CI 85.7-91.6%) of patients aged 18-23 years compared to 81.2% (95% CI 77.9-84.5%) in nomogram I; however, in 77% (95% CI 69.5-84.4%) versus 87.4% (95% CI 82.7-92.0%), respectively, among patients aged ≥ 30 years. In eyes with astigmatism ≥ 2 D, a postoperative astigmatism < 0.5 D was achieved in 89.4% (95% CI 83.0-95.7%) versus 72.9% (95% CI 64.3-81.5%), and a treatment efficacy index ≥ 0.9 was achieved in 100% versus 92.6% (95% CI 87.6-97.6%) with nomogram II versus nomogram I, respectively. CONCLUSION: There were several clinically significant benefits of the advanced nomogram in wavefront-optimized myopia PRK. On the other hand, there was a trend of lower accuracy in the older age group, warranting a second iteration.

Correlation between central corneal thickness and myopia.

PURPOSE: To analyze the correlation between central corneal thickness (CCT) and myopia in refractive surgery candidates. MATERIALS AND METHODS: Patients that underwent myopic laser refractive surgery between January 2000 and December 2014 were included. Preoperative CCT was measured by ultrasonic pachymetry, and refractive status determined by manifest and cycloplegic refraction. RESULTS: A total of 30,245 individuals were included. Mean age was 28.2 ± 8.6 years, and 45.9% were female. Mean refractive error was 4.02 ± 2.17 D (range 0.25-19.5), and the mean CCT measurement was 533.5 ± 35.5 µm (range 404-794). Younger individuals showed higher degree of myopia (p = 0.006). No difference in CCT was found between women and men (533.0 ± 35.1 and 533.6 ± 35.9 µm, respectively, p = 0.19). Though CCT showed no correlation with age (p = 0.226) participants above age 40 expressed higher CCT values (p < 0.001). No significant correlation was found between the CCT and cylinder (p > 0.05). An increase in mean keratometry was associated with a decrease in CCT (p < 0.001). There was a direct correlation between the degree of myopia and CCT (r = 0.94, p < 0.001). The result remained the same after adjusting for age group and gender in stepwise backward regression analysis (p < 0.001). CONCLUSION: Central corneal thickness is correlated with the degree of myopia among adults undergoing refractive surgery.

Tel-Aviv Protocol for Postrefractive Surgery Corneal Ectasia: A Case Series.

PURPOSE: The aim of this study was to describe the safety and efficacy of the Tel-Aviv Protocol (epithelial photorefractive keratectomy and corneal cross-linking) as a treatment for postrefractive surgery corneal ectasia. METHODS: This study includes 8 eyes from 7 patients, each diagnosed with postrefractive surgery ectasia years after refractive surgery and treated with the Tel-Aviv Protocol. The procedure included transepithelial PRK using the EX500 excimer laser, a 50-µm laser ablation of the epithelium and anterior stroma, delivered on the visual axis with cyclotorsion correction, treating up to 50% of refractive astigmatism. After the epithelial photorefractive keratectomy, all patients underwent corneal cross-linking. RESULTS: The mean keratometry (K) and maximal K both decreased [from 43.37 ± 2.23 to 41.84 ± 2.01 ( P = 0.03) and from 44.95 ± 3.08 to 42.78 ± 2.19 ( P = 0.03), respectively]. Astigmatism was significantly reduced (from 3.53 ± 2.36 to 0.88 ± 0.89 diopter; P = 0.02). Uncorrected visual acuity improved significantly in all patients from a mean of 0.56 ± 0.32 to 0.15 ± 0.14 logMAR ( P = 0.01). Best-corrected visual acuity improved from 0.22 ± 0.24 to 0.06 ± 0.06 logMAR ( P = 0.07; 1-tail P = 0.04). All patients maintained visual acuity during the follow-up period, up to 25 months, mean = 329 days. The Tel-Aviv Protocol was found to be safe [mean safety index: 1.63 ± 1.03 (range: 1.00-4)] and effective [mean efficacy index: 1.29 ± 0.66 (range: 0.71-2.1)]. CONCLUSIONS: The Tel-Aviv Protocol, developed initially for keratoconus treatment, is a safe and promising procedure to stop postrefractive surgery ectasia progression while significantly improving vision, thereby avoiding keratoplasty.

Photorefractive keratectomy in flat, normal, and steep corneas.

PURPOSE: To compare photorefractive keratectomy (PRK) outcomes in patients with different corneal steepness. SETTING: Care-Vision Laser Center, Tel-Aviv, Israel. DESIGN: Retrospective comparative chart review. METHODS: Patients included in this study underwent wavefront optimized myopic PRK between January 2013 and December 2019. Patients were divided into 3 groups based on the steepness of the cornea (steep keratometry) (flat: <42 diopters [D], normal: 42 to 46 D and steep: >46 D). One to one matching was performed to verify that baseline parameters (age, preoperative visual acuity and refractive error) were similar between groups. Primary outcome measures were: postoperative corrected/uncorrected distance visual acuity (CDVA/UDVA), efficacy index (postoperative UDVA/preoperative CDVA), safety index (postoperative CDVA/preoperative CDVA), spherical equivalence (SEQ) and cylinder. RESULTS: After matching, 650 eyes were included in each group, which were similar in baseline parameters. There were no significant postoperative differences between flat, normal, and steep corneas in terms of safety index (1.02 vs 1.03 vs 1.03, P = .28), efficacy index (1.01 vs 1.01 vs 1.02, P = .57), logMAR CDVA (0.01 vs 0.02 vs 0.01, P = .76), logMAR UDVA (0.02 vs 0.03 vs 0.02, P = .68), %SEQ within 0.50 D (73.9% vs 74.2% vs 74.6%, P = .95) or 1.00 D of target (91.9% vs 92.5% vs 92.2%, P = .92), %cylinder within 0.50 D (82.8% vs 82.2% vs 81.4%, P = .81) or 1.00 D of target (96.9% vs 97.1% vs 97.2%, P = .95). CONCLUSIONS: No significant differences were found between flat, normal and steep corneas following wavefront-optimized myopic PRK. Thus, this procedure may be safely and effectively performed in both flat and steep corneas.

Factors Predicting Loss of Best-Corrected Visual Acuity After Hyperopic Laser-Assisted In Situ Keratomileusis.

PURPOSE: The aim of this study was to identify risk factors for the loss of corrected distance visual acuity (CDVA) after uncomplicated hyperopic laser-assisted in situ keratomileusis (LASIK). METHODS: A retrospective study including hyperopic patients who underwent microkeratome-assisted LASIK between January 2000 and December 2019 at Care-Vision Laser Centers, Tel-Aviv, Israel. Loss of CDVA was defined as ≥ 2 lines (0.20 logarithm of the minimum angle of resolution [logMAR] increase). Excluded were patients who had loss of CDVA because of intraoperative or postoperative complications or developed cataract at their final visit. RESULTS: Overall, 1998 eyes of 1998 patients were included in the study, of which 35 eyes (1.75%) had CDVA loss at final follow-up (mean 387 days). The vision-loss group had a significantly greater spherical treatment (3.4 vs. 2.8 D, P = 0.02), ablation depth (69.4 vs. 53.8 µm, P = 0.01), a higher proportion of treatments with a smaller optic zone (6.0 mm) (31.4% vs. 13.4%, P = 0.002), treatment with the EX200 (Alcon) excimer rather than the EX500 (Alcon) (74.3% vs. 39.0%, P < 0.001), and treatment with the Moria M2-90 microkeratome rather than the Moria Sub-Bowman's keratomileusis (SBK) microkeratome (65.7% vs. 29.6%, P < 0.001). In multivariate binary logistic regression, factors that remained significant predictors of CDVA loss were a greater spherical treatment (per 1 D treatment, odds ratio = 1.42, 95% CI, 1.11-1.81, P = 0.004) and the use of the Moria M2-90 microkeratome (odds ratio = 4.66, 95% CI, 2.30-9.45, P < 0.001). CONCLUSIONS: In patients undergoing uncomplicated hyperopic LASIK, a greater spherical hyperopic treatment is associated with a higher risk for vision loss. Transition to a newer microkeratome model significantly reduced vision loss rate.

Hyperopic LASIK and postoperative corneal steepness: revisiting the 49-diopter limit.

PURPOSE: To compare corrected distance visual acuity (CDVA) outcomes of hyperopic laser in situ keratomileusis (LASIK) with a postoperative corneal steepness above vs below 49 diopters (D). SETTING: Care-Vision Laser Centers, Tel-Aviv, Israel. DESIGN: Retrospective study. METHODS: This study included consecutive patients who underwent hyperopic LASIK between January 2013 and December 2019. Hyperopic patients were divided into 2 groups based on postoperative corneal steepness with steep corneas defined >49.0 D and the control group ≤49.0 D. Adjustments were performed to account for differences in baseline and intraoperative parameters. RESULTS: Overall, 1703 eyes of 1703 patients were included. Mean age was 48.3 ± 10.0 years, and 45.3% were male. Preoperatively, the steep group (2.4%, n = 41/1703) had steeper mean (44.6 D vs 43.1 D, P < .001) and steep (45.1 D vs 43.5 D, P < .001) keratometry, worse logMAR CDVA (0.07 vs 0.04, P = .02), and higher sphere (4.9 D vs 2.9 D, P < .001). Intraoperatively, they had a higher spherical treatment (4.6 D vs 2.8 D, P < .001). After hyperopic LASIK, the steep group had worse logMAR CDVA (0.10 vs 0.06, P = .01). However, after accounting for differences in baseline and spherical treatment, no significant differences were found in postoperative logMAR CDVA (0.06 vs 0.06, P = .99). The factors that remained associated with worse postoperative CDVA were higher spherical treatment (0.01 logMAR per 1 D, P < .001) and preoperative CDVA (0.60 logMAR per 1.00 logMAR, P < .001). CONCLUSIONS: Postoperative corneal steepness greater than 49 D is not associated with worse visual outcomes after hyperopic LASIK. However, lower preoperative visual potential and higher spherical treatment applied are associated with worse outcomes. The 49 D cutoff should be revisited.

Laser-Assisted In Situ Keratomileusis in Flat, Normal, and Steep Corneas.

PURPOSE: To compare laser-assisted in situ keratomileusis (LASIK) outcomes in patients with different corneal curvatures. METHODS: This is a retrospective comparative chart review. Patients included in this study underwent wavefront-optimized myopic LASIK between January 2013 and December 2022 at Care-Vision Laser Center, Tel-Aviv, Israel. Patients were divided into 3 groups based on the steepness of the cornea (steep keratometry) (flat: <42 diopters [D], normal: 42-46 D, and steep: >46 D). Case-by-case matching was performed to verify that baseline parameters (age, preoperative visual acuity, and refractive error) were similar between groups. Primary outcome measures were postoperative corrected/uncorrected distance visual acuity, efficacy index, safety index, spherical equivalence, and astigmatism. RESULTS: After matching, 300 eyes were included in each group, which were similar in baseline parameters. There were no significant postoperative differences between flat, normal, and steep corneas regarding safety index (1.01 vs. 1.02 vs. 1.01, P = 0.95), efficacy index (1.03 vs. 1.02 vs. 1.02, P = 0.94), logarithm of the minimum angle of resolution corrected distance visual acuity (0.01 vs. 0.01 vs. 0.01, P = 0.17), logarithm of the minimum angle of resolution uncorrected distance visual acuity (0.02 vs. 0.03 vs. 0.02, P = 0.65), proportion of patients with spherical equivalence within 0.50 D (73.0% vs. 73.7% vs. 69.3%, P = 0.45) or 1.00 D (93.3% vs. 94.7% vs. 91.7%, P = 0.34) of the target, and proportion of patients with astigmatism within 0.50 D (86.7% vs. 82.3% vs. 80.3%, P = 0.11) or 1.00 D (98.7% vs. 98.7% vs. 99.0%, P = 0.91) of the target. Longer term follow-up of a smaller set of patients revealed similar results. CONCLUSIONS: No significant differences were found between flat, normal, and steep corneas following wavefront-optimized myopic LASIK. Thus, this procedure may be safely and effectively performed across a wide range of corneal curvatures.

Factors Predicting Slow Visual Recovery Following Myopic Photorefractive Keratectomy.

PURPOSE: To identify factors predicting slow visual recovery following photorefractive keratectomy (PRK). METHODS: This retrospective study included consecutive patients who underwent PRK between January 2005 and December 2019 at Care Vision Laser Center, Tel Aviv, Israel. Myopic patients were divided into 2 groups according to whether they experienced normal recovery of visual acuity (within 60 days) or slow visual recovery (>60 days). Visual recovery was defined as achieving an efficacy index of 0.9 or greater. Efficacy index was calculated as postoperative uncorrected visual acuity/preoperative best corrected visual acuity. A comparison of baseline and intraoperative parameters was performed. Binary logistic regression was performed to identify potential predictors of slow visual recovery. RESULTS: Overall, 4868 eyes were included. The mean age was 25.9 ± 7.7 years, and 53.9% were male. The slow visual recovery group (39.3%, n = 1911/4868) was older (P < 0.001) and had greater refractive astigmatism (P < 0.001) with a larger proportion of recent contact lens wearers (P = 0.002). The slow recovery group had larger optic zone treatments (P < 0.001), alcohol-assisted PRK (vs. transepithelial PRK) (P < 0.001), and greater maximum ablation depth (P < 0.001). In binary logistic regression, older age (P < 0.001), higher refractive astigmatism (P = 0.01), recent contact lens wear (P = 0.01), greater optic zone treatment (P = 0.001), and alcohol-assisted PRK (P < 0.001) remained significant predictors of slow visual recovery. CONCLUSIONS: Slow visual recovery was observed in ∼40% of patients following myopic PRK. Older age, greater refractive astigmatism, recent contact lens wear, greater optic zone treatment, and alcohol-assisted PRK were associated with slow visual recovery.

Factors predicting slow visual recovery following microkeratome-assisted myopic LASIK.

PURPOSE: To identify factors predicting slow visual recovery following myopic microkeratome assisted in situ keratomileusis (LASIK). DESIGN: Retrospective study. METHODS: This study included consecutive patients who underwent microkeratome-assisted myopic LASIK between January 2005 and December 2019 at Care Vision Laser Center, Tel Aviv, Israel. Patients were divided into three groups according to whether they experienced normal recovery of visual acuity (1 week visit), slow visual recovery (1 month visit) or very slow recovery (>1 month). Normal visual recovery was defined as achieving an efficacy index of 0.9 or greater. Efficacy index was calculated as postoperative uncorrected visual acuity/preoperative best corrected visual acuity. A comparison of baseline and intraoperative parameters was performed. RESULTS: Overall, 10 439 eyes were included. Mean age was 30.8 ± 8.7 years and 47.1% were females. The slower visual recovery groups (slow 11.4%, n = 1191; very slow 8.4%, n = 875) were of older age (p < 0.001), steeper preoperative steep keratometry (p = 0.002) and larger refractive astigmatism (p < 0.001). In binary logistic regression older age (p < 0.001), female gender (p = 0.001), larger astigmatism (p < 0.001) and high myopia (p < 0.001) remained significant predictors of slow visual recovery. CONCLUSION: Slow visual recovery was observed in 19.8% of patients following myopic LASIK. Older age, female gender, larger astigmatism and high myopia were associated with slow visual recovery. Patients may be advised accordingly.

Factors Predicting the Need for Re-treatment After Laser Refractive Surgery in Patients With Mixed Astigmatism.

PURPOSE: To identify risk factors that increase the likelihood of re-treatment following refractive surgery in patients with mixed astigmatism. METHODS: This was a retrospective study including patients who underwent either laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) between 2000 and 2019 and had mixed astigmatism (spherical error of +0.50 D or greater and spherical equivalent of less than 0.00 diopters [D]). Patients were divided into two groups according to whether they underwent re-treatments during the study period. RESULTS: Overall, 785 eyes (785 patients) were included. In total, 5.2% of the eyes (n = 41) underwent re-treatment. The re-treatment group was more likely to have preoperative high astigmatism (80.5% vs 48.3%, P < .001), moderate to high hyperopia (36.6% vs 22.3%, P = .035), and to have undergone surgery earlier during the study period (P < .001). They were also more likely to have undergone surgery using the Wave-Light EX200 rather than the EX500 laser platform (Alcon Laboratories, Inc) (P < .001), have a treated optical zone of 6 mm rather than 6.5 mm (P < .001 for both), and their maximum ablation depth was greater (P < .001). There was no difference between the re-treatment and control groups regarding procedure type (PRK vs LASIK). Binary logistic regression found preoperative high astigmatism (odds ratio = 3.97, P < .001) and the type of laser platform used (EX200, odds ratio = 7.78, P < .001) as the only independent factors associated with re-treatment. CONCLUSIONS: Re-treatment rates following correction of mixed astigmatism were 5.2% over 20 years. Use of a sixth-generation laser platform significantly reduced the risk of re-treatment. Presence of high astigmatism is a significant risk factor for re-treatment. There was no difference in retreatment risk between PRK and LASIK. [J Refract Surg. 2024;40(2):e73-e78.].

Factors Predicting Slow Visual Recovery Following Hyperopic LASIK.

PURPOSE: To identify factors predicting slow visual recovery following hyperopic laser in situ keratomileusis (LASIK). METHODS: The study included consecutive patients who underwent hyperopic LASIK between January 2005 and December 2019 at a single medical center. Patients were divided into two groups according to whether they experienced normal recovery of visual acuity (1-week visit) or slow visual recovery (1-month visit). Visual recovery was defined as achieving an efficacy index of 0.9 or greater. Efficacy index was calculated as postoperative uncorrected distance visual acuity / preoperative corrected distance visual acuity. A comparison of baseline and intraoperative parameters was performed. Binary logistic regression was performed to identify potential predictors of slow visual recovery. RESULTS: Overall, 861 eyes of 861 patients were included. Mean age was 48.0 ± 9.5 years and 55.9% were women. Two hundred forty-nine patients (28.9%) experienced slow visual recovery. Younger age (P = .01), a larger preoperative spherical equivalence (P = .002), and greater maximum ablation depth (P = .002) were predictors of slow visual recovery. In binary logistic regression, female gender (P = .036) and greater spherical equivalence (P = .007) remained significant predictors of slow visual recovery. CONCLUSIONS: Female gender and greater preoperative spherical equivalence were associated with slow visual recovery. Patients may be advised accordingly. [J Refract Surg. 2024;40(1):e42-e47.].

Factors Predicting Slow Visual Recovery Following Hyperopic LASIK.

PURPOSE: To identify factors predicting slow visual recovery following hyperopic laser in situ keratomileusis (LASIK). METHODS: The study included consecutive patients who underwent hyperopic LASIK between January 2005 and December 2019 at a single medical center. Patients were divided into two groups according to whether they experienced normal recovery of visual acuity (1-week visit) or slow visual recovery (1-month visit). Visual recovery was defined as achieving an efficacy index of 0.9 or greater. Efficacy index was calculated as postoperative uncorrected distance visual acuity / preoperative corrected distance visual acuity. A comparison of baseline and intraoperative parameters was performed. Binary logistic regression was performed to identify potential predictors of slow visual recovery. RESULTS: Overall, 861 eyes of 861 patients were included. Mean age was 48.0 ± 9.5 years and 55.9% were women. Two hundred forty-nine patients (28.9%) experienced slow visual recovery. Younger age (P = .01), a larger preoperative spherical equivalence (P = .002), and greater maximum ablation depth (P = .002) were predictors of slow visual recovery. In binary logistic regression, female gender (P = .036) and greater spherical equivalence (P = .007) remained significant predictors of slow visual recovery. CONCLUSIONS: Female gender and greater preoperative spherical equivalence were associated with slow visual recovery. Patients may be advised accordingly. [J Refract Surg. 2024;40(1):e42-e47.].

Mesopic pupil size in a refractive surgery population (13,959 eyes).

PURPOSE: To evaluate factors that may affect mesopic pupil size in refractive surgery candidates. METHODS: Medical records of 13,959 eyes of 13,959 refractive surgery candidates were reviewed, and one eye per subject was selected randomly for statistical analysis. Detailed ophthalmological examination data were obtained from medical records. Preoperative measurements included uncorrected distance visual acuity, corrected distance visual acuity, manifest and cycloplegic refraction, topography, slit lamp examination, and funduscopy. Mesopic pupil size measurements were performed with Colvard pupillometer. Relationship between mesopic pupil size and age, gender, refractive state, average keratometry, and pachymetry (thinnest point) were analyzed by means of ANOVA (+ANCOVA) and multivariate regression analyses. RESULTS: Overall mesopic pupil size was 6.45 ± 0.82 mm, and mean age was 36.07 years. Mesopic pupil size was 5.96 ± 0.8 mm in hyperopic astigmatism, 6.36 ± 0.83 mm in high astigmatism, and 6.51 ± 0.8 mm in myopic astigmatism. The difference in mesopic pupil size between all refractive subgroups was statistically significant (p < 0.001). Age revealed the strongest correlation (r = -0.405, p < 0.001) with mesopic pupil size. Spherical equivalent showed a moderate correlation (r = -0.136), whereas keratometry (r = -0.064) and pachymetry (r = -0.057) had a weak correlation with mesopic pupil size. No statistically significant difference in mesopic pupil size was noted regarding gender and ocular side. The sum of all analyzed factors (age, refractive state, keratometry, and pachymetry) can only predict the expected pupil size in <20% (R = 0.179, p < 0.001). CONCLUSIONS: Our analysis confirmed that age and refractive state are determinative factors on mesopic pupil size. Average keratometry and minimal pachymetry exhibited a statistically significant, but clinically insignificant, impact on mesopic pupil size.

Duration of contact lens removal before myopic refractive surgery.

PURPOSE: To compare refractive surgery outcomes in patients with different periods without contact lenses prior laser surgery. MATERIALS AND METHODS: Patients included in this study underwent myopic keratorefractive laser surgery between January 2005 and December 2014. Patients were divided into three groups based on the duration of time passed free of soft contact lens wearing prior to final preoperative evaluation and surgery (<24 h, 1-3 days or >3 days). Spectacle wearers served as a control group. Postoperative safety index, efficacy index and % of eyes within 0.5 D of the four groups were compared. A general linear model was used to compare main outcomes while adjusting for age, gender, preoperative measurements, and procedure type (LASIK vs PRK). RESULTS: Overall, 19,747 eyes were included. Soft contact lenses were worn by 42.3% (<24 h: 4.8%, 1-3 days: 18.5% and >3 days: 19.0%) and spectacles by 57.7% prior to surgery. In the PRK group, after adjusting for differences in baseline variables, the <24-h group had a significantly lower efficacy index than all the other groups. There were no significant differences between groups in terms of % eyes within ±0.5 D of intended correction (p = 0.55) or safety index (0.20). In the LASIK group, after adjusting for differences in baseline variables, there were no significant differences between groups in all primary outcomes. CONCLUSION: Soft contact lenses should be removed at least 24 h prior to final preoperative evaluation and refractive surgery, especially for patients undergoing PRK.

Outcomes of photorefractive keratectomy in patients with posterior corneal steepening.

PURPOSE: To assess post-operative outcomes following photorefractive keratectomy (PRK) in patients with posterior corneal steepening compared to an age, gender and refraction matched control group. METHODS: A retrospective matched case-control study that analysed outcomes of PRK in eyes with posterior corneal steepening as shown by the Sirius tomography (Sirius, CSO, Italy), versus normal eyes. Both groups were age, gender and refraction matched. Data collected include: demographic data, pre-operative and post-operative refraction, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), maximal ablation depth. Inferior-superior ratio, central corneal thickness (CCT), mean posterior keratometry (K), Baiocchi Calossi Versaci index for the front (BCVf) and back (BCVb) cornea, the symmetry index of front (SIf) and back (SIb) corneal curvature were assessed pre- and postoperatively. RESULTS: Overall, 89 study eyes and 954 normal myopic eyes were included. Compared to the control group, corneas with posterior steepening demonstrated significantly reduced CDVA (p < 0.0001 and p = 0.007) and lower CCT (p < 0.0001 and p = 0.03), before and following the operation, respectively. Pre-operative BCVf, BCVb, SIf and SIb were significantly higher in corneas with posterior steepening (p < 0.0001) and remained higher following the surgery except for BCVf. Ectasia occurred in one eye (1.1%). The safety and efficacy indices at 12 months were comparable for both groups. CONCLUSION: PRK on corneas with posterior steepening results in similar refractive outcomes compared to normal eyes, 1 year following the surgery. Keratectasia is a rare, however a possible complication.

Correlation between refractive state, corneal thickness, and keratometry in ametropic patients.

PURPOSE: To analyze the correlation between age, gender, refractive error, keratometry, and corneal thickness in a large group of subjects. METHODS: This study is a retrospective analysis of patients who underwent refractive surgery between January 2000 and February 2015 at Care Vision Refractive Clinic, Tel Aviv, Israel. Patient demographics, subjective refraction, pachymetry, and average keratometry were collected. RESULTS: Overall, 51,113 eyes of patients averaging 28.8 ± 9.3 years of which 53.9% were males were included. Average keratometry, spherical equivalent and cylindrical error differed significantly between male and female subjects (p < 0.001), while pachymetry did not (p = 0.332). In myopic eyes, correlations between age, pachymetry, average keratometry, spherical equivalent, and cylindrical error were all statistically significant except for the correlation between age and either pachymetry (p = 0.462) or spherical equivalent (p = 0.016). All correlations found were negligible or small (|r|= 0.003 to 0.141). In hyperopic eyes, correlations between age, pachymetry, average keratometry, spherical equivalent, and cylindrical error were all statistically significant except for the correlation between average keratometry and either pachymetry or cylindrical error (p = 0.344 or p = 0.274, respectively). All correlations found were negligible or small, except for a moderate correlation found between age and cylindrical error (r = 0.365). CONCLUSION: Refractive state, pachymetry, and keratometry of refractive surgery candidates are mostly weakly correlated.

Risk Factors for Dry Eye After Refractive Surgery.

PURPOSE: To determine the factors associated with clinically significant dry eye after keratorefractive surgery. METHODS: This is a large database retrospective study that included consecutive cases of myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy performed between 2008 and 2016 at Care-Vision Laser Center, Israel. Patients were divided into 2 groups according to whether they developed clinically significant dry eye. RESULTS: A total of 25,317 right eyes of 25,317 patients, with a mean age of 27.0 ± 8.3 years, were included. Postoperative dry eye developed in 1518 eyes (6.0%). The dry eye group was older (29.2 ± 9.0 vs. 27.6 ± 8.3 yrs, P < 0.001) and had a higher proportion of women (48.5% vs. 44.8%, P = 0.005), lower preoperative spherical equivalent (3.7 ± 2.0 vs. 4.0 ± 2.3D, P < 0.001), lower preoperative best-corrected visual acuity (0.019 ± 0.057 vs. 0.016 ± 0.064 Logarithm of the Minimum Angle of Resolution (LogMAR), P = 0.04), and lower proportion of preoperative soft contact lens wearers (40.6% vs. 45.5%, P < 0.001). In the postoperative dry eye group, a high proportion underwent LASIK (52.4% vs. 38.7%, P < 0.001) and were treated with a 7.0-mm (as opposed to 6.0 mm) optic zone (18.9% vs. 16.3%, P < 0.001). In multivariable analysis, older age [odds ratio (OR) 1.013, P < 0.001], female gender (OR 0.87, P = 0.009), lower preoperative refractive error (OR 1.05, P < 0.001), and LASIK (OR 0.67, P < 0.001) were associated with postoperative dry eye. CONCLUSIONS: Patients who are of older age, are of female gender, and have a lower preoperative refractive error and those undergoing LASIK are more likely to develop dry eye disease after keratorefractive surgery.

Risk Factors for Epithelial Ingrowth Following Microkeratome-Assisted LASIK.

PURPOSE: To analyze the incidence and risk factors associated with epithelial ingrowth following uncomplicated microkeratome-assisted LASIK. METHODS: All patients who underwent microkeratome-assisted LASIK between January 2006 and December 2014 in a single surgical center were reviewed. Epithelial ingrowth cases were identified and associated factors were assessed. RESULTS: Overall, 149 (0.49%) of 30,574 cases developed epithelial ingrowth. The epithelial ingrowth group was older compared to controls (35.3 ± 12.3 vs 31.7 ± 10.3 years, P = .001) and had a higher percentage of moderate to high hyperopia (13.7% vs 5.3%, P < .001), early postoperative flap slippage requiring flap repositioning (9.4% versus 2.8%, P < .001), or flap lifting for enhancement (48.6% vs 4.3%, P < .001), were treated with a smaller optic zone (6 mm) (37.7% vs 15.2%, P < .001), with a Moria M2 microkeratome (Moria SA, Antony, France) (70.1% vs 55.5%, P = .02), by low volume surgeons (n < 1,000) (5.8% vs 1.3%, P < .001), in a lower operating room temperature (22.3 ± 1.8 vs 22.8 ± 1.6, P = .005), and with a greater maximum ablation depth (67.3 ± 29.7 vs 57.3 ± 30.3, P < .001). There was a high incidence of epithelial ingrowth in the enhancement group compared to primary LASIK (4.8% vs 0.2%, P < .001). The time between treatments (primary and enhanced LASIK) was significantly greater in the epithelial ingrowth group (mean: 1,110 ± 870 vs 626 ± 662 days, P < .001). There was a significant rise in epithelial ingrowth rates as time between primary and enhancement LASIK increased, peaking at 4 to 5 years (P < .001). In multivariate analysis, flap lifting for enhancement (odds ratio [OR] = 19.5, P < .001), 6-mm optic zone (OR = 2.2, P < .001), moderate to severe hyperopia (OR = 2.4, P = .005), greater ablation depth (OR = 1.005, P < .001), and low volume surgeon (OR = 3.9, P = .01) were associated with epithelial ingrowth (total R2 = 15.4). CONCLUSIONS: The potential risk factors described above may forewarn surgeons as to which individuals merit closer observation for this complication. [J Refract Surg. 2018;34(2):100-105.].

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.].