Victor C.P. Woo

Contrast sensitivity after laser in situ keratomileusis: one-year follow-up

Purpose: To determine whether contrast sensitivity measurement, a more sensitive test of visual function than visual acuity, better characterizes visual outcomes after laser in situ keratomileusis (LASIK). Setting: Hong Kong Laser Eye Centre, Hong Kong, China. Methods: Contrast sensitivity was monitored in 41 LASIK patients for 1 year. Seven spatial frequencies (0.3, 0.8, 1.5, 3.4, 6.9, 10.3, and 20.5 cpd) were tested with 15 sequences per spatial frequency, and a staircase technique was used for target presentation. Results: There was a general depression in the contrast sensitivity function after LASIK; 1.5 cpd and 3.4 cpd were the most affected frequencies. Recovery took at least 6 months. The reduction in contrast sensitivity was greater for higher amounts of myopia. Conclusion: The post‐LASIK nonpermanent depression in contrast sensitivity was probably due to optical factors.

Vector analysis of astigmatic correction after small-incision lenticule extraction and femtosecond-assisted LASIK for low to moderate myopic astigmatism

Aim To compare astigmatic correction between femtosecond-assisted laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). Methods A total of 111 patients were included in this prospective study. Fifty-seven eyes were treated with LASIK and 54 eyes were treated with SMILE for myopia with low to moderate (−0.25 to −4.0 D) astigmatism. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity and manifest refraction were measured preoperatively and at 1 and 3 months postoperatively. Visual and refractive outcomes were reported. Changes in refractive astigmatism were evaluated using vector analysis. Results Preoperative characteristics were similar between both groups. The UDVA at 1 and 3 months was better in the LASIK group compared with the SMILE group (p<0.009). Postoperative cylinder was higher in the SMILE group (p<0.001). Fewer eyes attained the attempted cylindrical correction in the SMILE group (p<0.029). Vector analysis showed no significant difference in target-induced astigmatism (p=0.091) and angle of error (p>0.596) between the two groups. Surgically induced astigmatism was significantly lower in the SMILE group (p<0.023), while the difference vector (p<0.001) and absolute angle of error (p<0.016) were significantly higher in the SMILE group. No significant difference was found in these parameters between 1 and 3 months in both groups (p>0.122). Conclusions Our results showed that SMILE offered a less favourable astigmatic correction comparable to femtosecond-assisted LASIK in eyes with low to moderate myopic astigmatism. The alignment of treatment was more variable in SMILE, leading to a lower efficacy compared with LASIK by 3 months postoperatively.

Vector Analysis of Corneal Astigmatism After Combined Femtosecond-Assisted Phacoemulsification and Arcuate Keratotomy

PURPOSE To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. DESIGN Retrospective, interventional case series. METHODS This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector analysis of the astigmatic changes was performed using the Alpins method. RESULTS Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively (P < .001). The magnitude of error (difference between surgically induced and target-induced astigmatism) (-0.13 ± 0.68 D), as well as the correction index (ratio of surgically induced and target-induced astigmatism) (0.86 ± 0.52), demonstrated slight undercorrection. The angle of error was very close to 0, indicating no significant systematic error of misaligned treatment. However, the absolute angle of error showed a less favorable range (17.5 ± 19.2 degrees), suggesting variable factors such as healing or alignment at an individual level. There were no intraoperative or postoperative complications. CONCLUSIONS Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies.

Intraocular pressure profiles during femtosecond laser-assisted cataract surgery.

Purpose To document the intraocular pressure (IOP) profiles during femtosecond laser–assisted cataract surgery. Setting Refractive cataract surgery center. Design Prospective case series. Methods Intraocular pressure was measured using a handheld portable applanation tonometer (Tono‐Pen Avia) during femtosecond laser–assisted cataract surgery using the Victus platform. Results Forty‐one eyes of 35 patients were recruited. The mean age of the patients was 70.5 years ± 8.2 (SD) (range 51 to 85 years). The mean IOP before, during, and after suction was 17.2 ± 3.2 mm Hg (range 10 to 23 mm Hg), 42.1 ± 10.8 mm Hg (range 20 to 55 mm Hg), and 13.8 ± 3.4 mm Hg (range 9 to 25 mm Hg), respectively. The mean difference between IOP before and during suction was 25.0 ± 11.3 mm Hg (range 5 to 43 mm Hg) (P<.01, Wilcoxon signed‐rank test). The mean difference between IOP during and after suction was −28.7 ± 10.8 mm Hg (range −45 to −10 mm Hg) (P<.01, Wilcoxon signed‐rank test). The mean suction duration was 216 ± 15 seconds (range 180 to 245 seconds). Conclusions The increase in IOP during the suction phase of femtosecond laser–assisted cataract surgery was statistically significant compared with the baseline IOP. Caution should be taken in patients with ocular conditions that are vulnerable to IOP fluctuation. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Excimer laser photorefractive keratectomy for myopia: Six-month follow-up

Abstract In this study, 108 eyes of 62 patients had photorefractive keratectomy (PRK) with a 193 nm excimer laser to correct myopia. The eyes were assigned to one of three groups: low, moderate, or high myopia. Six months after PRK, 88.9% of eyes in the low myopia group, 90.0% in the moderate myopia group, and 23.8% in the high myopia group achieved an uncorrected visual acuity of 20/40 or better. In the low myopia group, 88.9% were within ±1 diopter (D) of attempted correction, as were 70.0% in the moderate group and 18.8% in the high myopia group. There were no significant complications. We conclude that excimer laser PRK appears to be a safe and relatively accurate procedure to correct low to moderate myopia but not high myopia because of regression over time.

Effect of the Learning Curve on Visual and Refractive Outcomes of Small-incision Lenticule Extraction

Purpose: To investigate the effect of the learning curve for small-incision lenticule extraction during the first 2 years of experience. Methods: Small-incision lenticule extraction was performed using the 500-kHz VisuMax femtosecond laser (Carl Zeiss Meditec) by the same surgeon. The initial 100 patients since the surgeon started operating independently were considered as group 1; the recent 100 patients were considered as group 2. The same laser settings and technique were used. The visual and refractive outcomes were compared between groups at postoperative 1 week and 6 months. Vector analysis was performed for eyes with astigmatic correction. Results: Two hundred right eyes of 200 patients were included. Age, preoperative corrected visual acuity, manifest refraction, and central corneal thickness were similar between groups (P ⩽ 0.154). Postoperatively, the efficacy index at 1 week was better in group 2 (group 1: 0.85 ± 0.16 vs. group 2: 0.91 ± 0.10, P = 0.019) but was similar between groups at 6 months (group 1: 0.91 ± 0.14 vs. group 2: 0.94 ± 0.08, P = 0.181). The safety index was higher in group 2 at 1 week (group 1: 0.93 ± 0.10 vs. group 2: 0.95 ± 0.08, P = 0.045) and 6 months postoperatively (group 1: 0.97 ± 0.07 vs. group 2: 0.99 ± 0.03, P = 0.011). Vector analysis showed that postoperative residual astigmatism and misalignment of astigmatic correction were lower in group 2 than in group 1 (P ⩽ 0.039) at 1 week and 6 months. The duration of docking and that of lenticule extraction was shorter in group 2 (P ⩽ 0.034). Conclusions: Our study showed that faster visual recovery, better safety profile, and more accurate astigmatic correction could be attained with increasing surgical experience.

Comparison of the Early Clinical Outcomes between Combined Small-Incision Lenticule Extraction and Collagen Cross-Linking versus SMILE for Myopia

Background. To compare the early outcome of combined SMILE and collagen crosslinking (SMILE Xtra) with SMILE. Method. Prospective, comparative interventional study of 21 eyes receiving SMILE Xtra using a low energy protocol and 32 control eyes receiving SMILE only. The outcomes were compared at 1, 3, and 6 months postoperatively. Results. Both groups had myopia with spherical equivalent refraction (SEQ) > 4.00 D. The SMILE Xtra group had thinner preoperative central corneal thickness and residual stromal bed thickness (p < 0.021). At 6 months, no eyes lost more than 1 line in corrected distance visual acuity. The safety index was 0.96 ± 0.06 and 1.00 ± 0.00 in SMILE Xtra and control, respectively (p < 0.001). 89% and 94% of eyes were within ±0.50 D of target refraction, respectively, with the mean error in SEQ correction being −0.17 ± 0.26 D for SMILE Xtra and +0.03 ± 0.25 D for control (p = 0.021). The efficacy index was 0.88 ± 0.13 and 0.97 ± 0.06, respectively (p = 0.005). Conclusion. SMILE Xtra had good overall safety profile and predictability at 6 months. However, when compared with control, the safety index and efficacy index were statistically significantly lower in the early postoperative period.

Objective method to measure corneal clarity before and after laser in situ keratomileusis

Purpose: To develop, evaluate, and use an objective method to determine the effect of laser in situ keratomileusis (LASIK) on corneal clarity. Setting: Centre for Myopia Research, The Hong Kong Polytechnic University, and the Hong Kong Laser Eye Center, Hong Kong, China. Methods: Color photographs of corneal sections were taken using a digital camera and converted to 8‐bit gray‐scale images. The desired area of the photograph was isolated using a preset mask, and a gray‐scale or corneal clarity index of the desired area was obtained by averaging the “intensity” indices of individual pixels within the area. The reliability of the clarity index measures was determined by comparing test and retest measures. The sensitivity of the method was quantified by its ability to identify a small (clinically undetectable) decrease in corneal clarity produced by tight‐fitting soft contact lenses worn for 30 minutes. Finally, corneal clarity was measured and compared in 24 patients before and 1 day, 1 week, and 1 month after LASIK. Results: The reliability value was 4.11 corneal clarity units, and the change in corneal clarity due to soft contact lens use was 16.24 units. In the LASIK patients, there were statistically significant decreases in corneal clarity from preoperatively to 1 day and 1 week but not to 1 month. Conclusions: The method measured changes in corneal clarity that were undetectable clinically and were 4 times greater than 95% of the differences between test and retest measures. The method is therefore reliable and sensitive. Corneal clarity decreased after LASIK and recovered within approximately 1 month.

Presbyopic Correction Using Monocular Bi-aspheric Ablation Profile (PresbyMAX) in Hyperopic Eyes: 1-Year Outcomes

PURPOSE To present the 1-year outcomes of combining monocular bi-aspheric ablation profile and contralateral monofocal LASIK in hyperopic patients with presbyopia. METHODS In this retrospective case series, 36 consecutive patients (72 eyes) who underwent simultaneous bi-aspheric ablation (PresbyMAX: SCHWIND Eye-Tech-Solutions GmbH and Co KG, Kleinostheim, Germany) in the non-dominant eye and monofocal regular LASIK in the dominant eye for correction of hyperopia and presbyopia were reviewed for 1 year. Binocular uncorrected distance (UDVA), near (UNVA), corrected distance (CDVA), and distance corrected near (DCNVA) visual acuity and manifest refraction were analyzed postoperatively. RESULTS At 1 year, the mean binocular UDVA improved significantly from 0.26 ± 0.25 to 0.039 ± 0.088 logMAR (P < .001). Binocular UNVA also improved from 0.73 ± 0.30 to 0.10 ± 0.22 logRAD (P < .001). Eighty-seven percent of patients achieved UDVA of 20/25 or better and 90% had UNVA of J3 or better. Simultaneous binocular distance and near vision of 20/25 and J2 or better was achieved in 70%. Only 17% of patients had a binocular DCNVA of J2 or better. No patient suffered from a loss of 2 lines of CDVA. Refractive stability was achieved for both eyes from 1 month postoperatively. The re-treatment rate was 14% for improvement of near vision within 6 months to 1 year. CONCLUSIONS Presbyopic correction using monocular PresbyMAX combined with monofocal regular LASIK in the fellow eye is safe and acceptable in hyperopic patients. [J Refract Surg. 2017;33(1):37-43.].

Effect of location of opening incision on astigmatic correction after small-incision lenticule extraction

We compared the visual and refractive outcomes between 2 different incisional sites in small incision lenticule extraction (SMILE) for low myopic astigmatism. This was a contralateral eye study. Consecutive cases that underwent bilateral SMILE surgery were included. Procedures for both eyes were identical apart from the location of opening incision. The incision was set on the temporal side for the right eye (Group 1), while a superior incision was set for the left eye (Group 2). Twenty-nine patients with a mean age of 35.0 ± 9.6 years were included. Preoperative visual and refractive parameters were comparable between the 2 groups (p > 0.250). At 3 months, the logMAR uncorrected distance visual acuity was 0.074 ± 0.090 in Group 1 and 0.084 ± 0.130 in Group 2 (p = 0.861). No difference was found in the postoperative manifest spherical equivalent (p = 0.501) and manifest cylinder (p = 0.178) between the 2 groups. The efficacy index was 0.85 ± 0.16 in Group 1 and 0.85 ± 0.20 in Group 2 (p = 0.828). Astigmatic correction was not significantly affected by the location of opening incisions using vector analysis. Our study did not find significant differences in visual and refractive outcomes with temporal or superior opening incision during SMILE surgery.