Silvania Lau

Central corneal thickness measurements using Orbscan II, Visante, ultrasound, and Pentacam pachymetry after laser in situ keratomileusis for myopia

PURPOSE: To compare corneal pachymetry assessment using 4 measurement methods in eyes after laser in situ keratomileusis (LASIK) for myopia. SETTING: Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Hong Kong SAR. METHODS: Fifty‐two consecutive patients (103 eyes) who had LASIK for the correction of myopia had Orbscan II (Bausch & Lomb), Visante (Carl Zeiss Meditec), Pentacam (Oculus, Inc.), and ultrasound (US) pachymetry (Sonomed, 200P) 6 months after surgery. Data were analyzed using the paired sample t test, Bland‐Altman plots, and linear regression. RESULTS: The mean postoperative pachymetry measured by US, Orbscan (0.89 acoustic factor), Pentacam, and Visante pachymetry were 438.2 μm ± 41.18 (SD), 435.17 ± 49.63 μm, 430.66 ± 40.23 μm, and 426.56 ± 41.6 μm, respectively. Compared with the US measurement, Pentacam and Visante measurements significantly underestimated corneal thickness by a mean of 7.54 ± 15.06 μm (P<.01) and 11.64 ± 12.87 μm (P<.01), respectively. There was no statistically significant difference between US and Orbscan measurements. CONCLUSION: Pentacam and Visante measurements of corneal thickness 6 months after LASIK were significantly less than those obtained using Orbscan and US pachymetry, although all 4 measurement methods showed a high correlation with each other.

Visual Outcomes and Patient Satisfaction After Presbyopic Lens Exchange With a Diffractive Multifocal Intraocular Lens

PURPOSE To investigate the visual outcomes, severity of symptoms, and patient satisfaction after refractive lens exchange (RLE) with a diffractive multifocal intraocular lens (IOL). METHODS A nonrandomized, unmasked, retrospective chart review study was performed. Patients who underwent RLE with ZMA00 (Abbott Laboratories) were identified from a hospital database. Eyes with preoperative uncorrected distance visual acuity or corrected distance visual acuity 20/20 or better were included. The study cohort comprised 45 eyes from 29 patients. Monocular uncorrected and distance-corrected visual acuity at distance, 67 cm, and 30 cm were measured 6 months postoperatively. A patient questionnaire assessing visual symptoms (halo, night glare, and starburst) and satisfaction with visual performance was administered. RESULTS Six months postoperatively, mean uncorrected visual acuity (logMAR) was -0.10±0.13, 0.43±0.25 at 67 m (intermediate), and 0.18±0.05 at 30 m (near). Mean distance-corrected visual acuity at these distances was -0.02±0.06, 0.40±0.21, and 0.17±0.02, respectively. Twenty-seven patients completed the questionnaire. Patients reported postoperative halos (78%), night glare (26%), and starbursts (48%). All bilateral RLE patients were spectacle-free at all distances, whereas 50% of unilateral RLE patients required spectacles postoperatively. Bilateral RLE patients with habitual spectacle use preoperatively were the most satisfied with their postoperative visual performance. CONCLUSIONS Refractive lens exchange with the ZMA00 is an option for presbyopic correction; however, significant glare, halo, and starburst issues are subjectively reported.

Conductive keratoplasty to treat hyperopic overcorrection after LASIK for myopia.

PURPOSE to investigate the refractive outcomes and stability of conductive keratoplasty (CK) for retreatment of myopic LASIK overcorrection. METHODS seven eyes (six patients) that were overcorrected after myopic LASIK by +1.00 to +2.75 diopters (D) manifest refraction spherical equivalent (MRSE) were retreated using CK. All eyes had insufficient stromal thickness for LASIK retreatment. LightTouch CK was performed at least 1 year after LASIK. Either 8 or 16 spots were applied at 7- and/or 8-mm zones on the cornea. Uncorrected distance visual acuity, manifest refraction, corrected distance visual acuity (CDVA), and postoperative complications were analyzed. RESULTS mean MRSE after CK at last follow-up was +0.38 ± 0.52 D (range: -0.38 to +1.13 D). The change in MRSE ranged from -0.63 to -2.38 D. Mean MRSE after CK changed from -0.60 ± 2.07 D (range: -3.38 to +1.50 D) at 1 week to +0.45 ± 0.69 D (range: -0.38 to +1.38 D) at 12 months. Two eyes experienced an initial overcorrection of -2.75 D and -3.38 D, respectively, at 1 week after CK. Cylinder ≤0.75 D was induced in four eyes, whereas one eye had a 0.75-D reduction in cylinder. All eyes had CDVA of logMAR 0.10 or better. Two eyes lost one line of CDVA and no eyes lost more than one line. CONCLUSIONS lighttouch CK retreatment for over-corrected myopic LASIK can reduce the hyperopia but produces minimal change in cylinder, and may be appropriate for eyes with insufficient stromal tissue for repeated excimer laser surgery. Early regression occurs commonly.

Intraoperative flap re-cut after vertical gas breakthrough during femtosecond laser keratectomy

We describe the management of intraoperative vertical gas breakthrough (VGB) during femtosecond laser flap creation in 3 patients. All eyes were immediately re-cut using 2 different microkeratomes, and the laser in situ keratomileusis treatments were completed on the same day. There were no postoperative complications. Corneal abrasion might predispose to VGB. Management of VGB is effective using microkeratomes. Caution is advised during placement of the suction ring and in eyes with preexisting corneal abrasion or loose epithelium if femtosecond laser keratectomy is used. The approach in terms of direction of the microkeratome re-cut is fundamental to the safety and successful re-cut with a microkeratome.

Introducing a new ratio useful in the estimation of preoperative corneal power in patients with myopic LASIK based on postoperative corneal data.

Aim: The aim of this study was to establish a new constant ratio for the calculation of preoperative total corneal power using postoperative corneal data alone in patients after laser in situ keratomileusis (LASIK). Methods: Preoperative anterior and posterior corneal radii from 192 pre-LASIK eyes were analyzed to derive a constant ratio in the first part of the study. In the second part of the study, with a set of post-LASIK patients (98 eyes), this ratio was used to estimate preoperative total corneal power. This estimated total corneal power was compared with the true value obtained from direct preoperative measurement. Results: The ratio (Rroc) between the preoperative anterior central 10-mm corneal curvature and the posterior peripheral 7- to 10-mm corneal curvature was 1.166 ± 0.049. Estimated mean preoperative total corneal power was 43.42 ± 2.21 D, whereas the true preoperative mean keratometric value (SimK) was 43.40 ± 2.64 D. The mean difference was 0.02 ± 2.65 D (P = 0.942). Conclusions: The pre-LASIK corneal power can be estimated using post-LASIK data together with Rroc. This will be useful in post-LASIK patients requiring cataract surgery but without the availability of pre-LASIK corneal data for the estimation of the preoperative keratometric power when the double-K technique was used to calculate the intraocular lens power.

Correlation Between Axial Length and Anterior Chamber Depth in Normal Eyes, Long Eyes, and Extremely Long Eyes.

Purpose The objective of this study was to investigate the correlation between axial length (AL) and anterior chamber depth (ACD) in normal to long eyes and in extremely long eyes. Design This was an observational cross-sectional study in a single-center, private hospital. Methods Axial length and ACD data were retrieved from the intraocular lens (IOL) Master database of patients who presented for IOL or phakic lens implantation. Only left eyes were included. The correlation between AL and ACD was tested with Pearson correlation coefficient in all eyes, normal to long eyes (AL < 27.5 mm), and extremely long eyes (AL ≥ 27.5 mm). P < 0.01 was statistically significant. Results The cohort was composed of 1184 eyes of 1184 Chinese patients. The mean age was 65.8 ± 13.3 years (range, 19–98 years). The mean AL and ACD were 24.73 ± 2.48 mm (range, 20.51–36.20 mm) and 3.09 ± 0.44 mm (range, 1.95–4.68 mm), respectively. Pearson correlation coefficients in all eyes, normal to long eyes (1026 eyes, 87%), and extremely long eyes (158 eyes, 13%) were 0.56 (P < 0.001), 0.59 (P < 0.001), and −0.15 (P = 0.67), respectively. Conclusions There was a statistically significant positive correlation between AL and ACD in normal and long eyes but not in extremely long eyes. No correlation between AL and ACD in extremely long eyes requires newer-generation IOL formulas (ACD included) to increase the accuracy of IOL implantation.

Comparison of corneal flap thickness between primary eyes and fellow eyes using the Zyoptix XP microkeratome

PURPOSE: To evaluate corneal flap thickness created in myopic laser in situ keratomileusis (LASIK) using the Zyoptix XP 120 microkeratome (Bausch & Lomb). SETTING: University‐based eye clinic. METHODS: Corneal thickness was measured preoperatively and intraoperatively after flap creation in 62 consecutive patients (124 eyes) who had LASIK for the correction of myopia. Corneal flap thickness was calculated by subtracting stromal bed thickness from total corneal thickness. In each patient, both corneas (right followed by left) were cut by 1 the same Zyoptix XP 120 microkeratome blade at the same session. RESULTS: The mean actual flap thickness was 115.34 μm ± 16.34 (SD) in right eyes and 104.55 ± 14.34 μm in left eyes. The mean actual flap thickness in right eyes was not statistically significantly different from the 120 μm proposed by the manufacturer (P = .142); however, the mean actual flap thickness in left eyes was statistically significantly different from the 120 μm (P<.001). The mean flap thickness in the second eye was also statistically significantly thinner than in the first eye (P<.001). CONCLUSIONS: The corneal flaps were thinner than expected when a Zyoptix XP 120 microkeratome was used in LASIK. Although the first cuts produced thinner flaps, this difference was not statistically significant. However, the second cuts produced significantly thinner flaps.