Arthur C.K. Cheng

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.

Descemet Stripping Endothelial Keratoplasty: Effect of the Surgical Procedure on Corneal Optics

PURPOSE To determine the changes in corneal optical performance after posterior lamellar corneal transplantation. DESIGN Retrospective case series. METHODS The anterior segment in four eyes of four patients who underwent Descemet stripping endothelial keratoplasty (DSEK) with cataract extraction and intraocular lens (IOL) implantation were imaged with the Visante anterior segment optical coherence tomography [OCT] (Carl Zeiss Meditec, Dublin, California, USA). The curvature of the posterior surface of the donor graft was compared with that of the host cornea, and corneal thickness was measured. RESULTS All eyes had a hyperopic refractive error after surgery. The posterior corneal curvature after surgery was more than that before surgery. Average preoperative keratometry was 43.4 diopters (D), and after surgery, it was 42.8 D using keratometry. However, when the postsurgical corneal power was calculated using the Gaussian optics method, the average value was 40.8 D. CONCLUSIONS The addition of a donor corneal graft to the posterior surface of decompensated corneas may lessen the effective optical power of the cornea and may have implications for IOL power calculations in these eyes.

Pathogenesis and management of laser in situ keratomileusis flap buttonhole

PURPOSE To describe the clinical features and outcomes in patients who had a flap buttonhole during laser in situ keratomileusis (LASIK) and propose an etiopathogenic mechanism for this complication. SETTING University Eye Center, Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China. METHODS Retrospective review of case records of 6 patients (6 eyes) who had a flap buttonhole during LASIK. RESULTS The mean patient age was 38.2 years +/- 4.1 (SD) and the mean preoperative spherical equivalent (SE) refraction, -8.13 +/- 4.04 diopters (D). Mean keratometry was 44.20 +/- 1.30 D. Retreatment was performed after a mean interval of 9.2 +/- 3.2 months. Final postoperative SE refraction was -0.44 +/- 0.58 D after a mean follow-up of 59.0 +/- 5.3 weeks. No patient experienced loss of best spectacle-corrected visual acuity. CONCLUSIONS Retreatment of eyes that have a flap buttonhole during LASIK is associated with good visual outcomes. Flap buttonholes can produce alterations in refraction, so retreatment is best performed after the refractive error has stabilized. Microkeratome malfunction may be responsible for the occurrence of a flap buttonhole during LASIK in eyes that do not have significant corneal steepening.

Management of severe flap wrinkling or dislodgment after laser in situ keratomileusis

PURPOSE To review the management and results of cases with severe flap wrinkling or dislodgment after laser in situ keratomileusis (LASIK). SETTING University Eye Center, Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, The Chinese University of Hong Kong. METHODS Four patients with severe flap wrinkling or dislodgment after LASIK are described. Surgical repositioning of the flap was performed in all cases. Flap status, refractive changes, and final uncorrected and best corrected visual acuities were used to evaluate the outcome of flap repositioning. RESULTS Flap repositioning required suturing in 2 patients, 1 of whom developed severe epithelial ingrowth with melting of the corneal flap and stromal bed and eventually required flap removal. The stromal inflammation resolved, and the corneal surface re-epithelialized after flap excision. In 2 other patients, wedge-shaped tissue excision (1.0 x 1.5 mm) from the superior portion of the corneal flap was necessary to allow better flap realignment. In 1 of these patients, the corneal flap was eventually converted to a free cap to correct residual wrinkling. At a mean follow-up of 15 months, the postoperative uncorrected visual acuity ranged from 20/20 to 20/60, and the best spectacle-corrected visual acuity (BSCVA) was 20/30 or better in all patients. In 1 patient, BSCVA decreased by 1 line. CONCLUSIONS Flap dislodgment and wrinkling are serious postoperative complications of LASIK. Early recognition of these complications and prompt surgical management are crucial to achieve a successful surgical and visual outcome.

Corneal collagen cross-linking demarcation line depth assessed by Visante OCT After CXL for keratoconus and corneal ectasia.

PURPOSE To report the demarcation line depth after corneal collagen cross-linking (CXL) for keratoconus and postoperative LASIK ectasia with Visante (Carl Zeiss Meditec) optical coherence tomography (OCT) and investigate correlations between this depth and preoperative parameters and postoperative visual and keratometry outcomes. METHODS Retrospective interventional case series of 40 eyes with keratoconus or postoperative LASIK ectasia treated with riboflavin ultraviolet-A CXL. Ophthalmic evaluation included uncorrected distance visual acuity, corrected distance visual acuity (CDVA), corneal topography (Pentacam, Oculus Optikgeräte GmbH), and postoperative anterior segment OCT. Correlation analyses were performed. Statistical significance was indicated by P<.05. RESULTS At 6 months postoperative, mean demarcation line depth was 281.4±53.3 μm. Thinner minimal corneal thickness (r=0.413, P=.008), older age (r=-0.490, P=.001), higher grading of ectasia (for both keratoconus and postoperative LASIK ectasia) (r=-0.332, P=.044), female sex (r=0.343, P=.030), postoperative LASIK ectasia (r=-0.420, P=.007), and longer duration of disease (r=-0.377, P=.023) were correlated with shallower demarcation line depth. Forward stepwise multiple linear regression analysis showed that among all preoperative factors, minimal corneal thickness (standardized β=0.473, P=.003) and age (standardized β=-0.317, P=.036) were significantly associated with demarcation line depth. The CXL demarcation line depth and change in CDVA (r=-0.16, P=.325) and change of the steepest keratometry at 6 months (r=0.084, P=.637) were not correlated. CONCLUSIONS The Visante OCT can be used for assessing CXL demarcation line depth. The demarcation line depth may decrease with the severity of ectasia and age.

Conventional versus accelerated corneal collagen cross‐linking in the treatment of keratoconus

Background This study aims to compare the effect of conventional corneal collagen cross-linking (CXL) with accelerated corneal collagen cross-linking in treatment of keratoconus. Design A comparative interventional study was employed. Participants Participants were consecutive cases of progressive keratoconus receiving either conventional (3 mW/cm2 irradiance for 30 min) or accelerated CXL (9 mW/cm2 irradiance for 10 min). Methods Clinical and topographic parameters were compared between the two groups. Postoperative corneal stromal demarcation line was measured using anterior segment optical coherence tomography. Main Outcome Measures Clinical and topographic parameters such as corrected distant visual acuity (CDVA), maximum keratometry (Kmax), mean keratometry (Kmean), demarcation line depth were gathered from medical records. Results There were a total of 26 eyes with an average follow up of 13.9 ± 6.3 months. Fourteen eyes received conventional CXL, and 12 eyes had accelerated CXL. In the conventional CXL group, CDVA improved significantly (P = 0.021). There was also a significant reduction in Kmax (P = 0.003) and Kmean (P = 0.002). In the accelerated CXL group, no significant changes were found in CDVA (P = 0.395), Kmax (P = 0.388) and Kmean (P = 0.952) postoperatively. A significantly greater reduction in Kmax and Kmean were seen in conventional CXL compared to its accelerated counterpart (P = 0.001 and 0.015, respectively). The demarcation line was deeper in eyes with conventional CXL (P = 0.013), and the depth correlated significantly with the change in Kmean (r = −0.432, P = 0.045). Conclusion Conventional and accelerated CXL are effective in stabilizing keratoconus progression after a mean of 12 months. Patients undergoing conventional CXL showed clinical improvement with greater corneal flattening, which correlated with a deeper corneal stromal demarcation line. This current study is the first to report such correlation.This study aims to compare the effect of conventional corneal collagen cross‐linking (CXL) with accelerated corneal collagen cross‐linking in treatment of keratoconus.

Late Traumatic Flap Dislocations After LASIK

PURPOSE To report the management and outcome of late onset traumatic dislocation of LASIK flaps. METHODS This retrospective, interventional case series presents three patients with late onset LASIK flap dislocation following mechanical trauma 1 to 7 years postoperatively. RESULTS In all cases, the flap was surgically repositioned. Epithelial ingrowth was removed and diffuse lamellar keratitis was treated with an intensive steroid regimen. All patients returned to their preoperative best spectacle-corrected visual acuity. Aggressive steroid treatment during the perioperative period and meticulous handling of the epithelium are important in preventing further recurrence. CONCLUSIONS Laser in situ keratomileusis flaps may experience mechanical dislocation as late as 7 years postoperatively. Diffuse lamellar keratitis and epithelial ingrowth are associated with flap dislodgment.

Pachymetry Assessment With Orbscan II in Postoperative Patients With Myopic LASIK

PURPOSE To compare central corneal thickness after LASIK for myopia, using ultrasonic pachymetry and Orbscan II measurements, and to evaluate changes in these measurements over time. METHODS Central corneal thickness measurements obtained by ultrasonic pachymetry and Orbscan II (Bausch and Lomb, Rochester, NY) in patients who underwent myopic LASIK between July 2002 and May 2003 were analyzed. The two measurements were assessed preoperatively and postoperatively at 1 day and 1, 3, 6, and 12 months. RESULTS In 237 eyes, using the correction factor 0.93, no significant difference was noted in the preoperative central corneal thickness measured by ultrasonic pachymetry (561.89 +/- 28.66 microm) and Orbscan pachymetry (562.28 +/- 28.18 microm) (P =.713). Postoperatively, the difference was statistically significant at day 1 and 1, 3, and 6 months (P < .001), but was not significant at 12 months (P = .130). CONCLUSIONS Orbscan II measurements of central corneal thickness after myopic LASIK are less than those measured by ultrasonic pachymetry; however, this difference decreases with time and may not be significant after 1 year.

Assessment of pupil size under different light intensities using the Procyon pupillometer

PURPOSE: To study the relationship between pupil size and light intensity using the Procyon pupillometer. SETTING: University based clinic. METHODS: In this retrospective study, 20 consecutive patients had pupil size assessment with the Procyon pupillometer under 3 different light conditions—4, 0.4, and 0.04 lux. Correlation was established using the log unit of the light intensity and pupil size. RESULTS: The correlation coefficient for the association between pupil size and log unit of light intensity in all eyes was significant (P<.001). The mean correlation coefficient for the association between pupil size and log unit of light intensity in all patients was 0.968 ± 0.089 (SD) in the right eye and 0.970 ± 0.031 in the left eye. CONCLUSION: The linear relationship between the pupil size and the log unit of the light intensity showed a tight correlation in all cases. These results can be useful in the comparing pupil size with pupillometers that work under different light conditions.

Culture-negative ulcerative keratitis after laser in situ keratomileusis

A 40-year old man, highly myopic in both eyes, had laser in situ keratomileusis (LASIK) in the left eye in November 1996. Corneal melting and ulceration and fine striae-like interface infiltrates were noticed 1 day postoperatively. There was no response to intensive topical antibiotics in the form of hourly ofloxacin 3% (Tarivid), and satellite lesions developed on day 4. Corneal scrapings for gram stain and culture were done twice. No bacterial or fungal organisms were identified. Intensive topical fortified vancomycin (50 mg/mL) was added, and the lesions resolved gradually over the ensuing 2 weeks. Eighteen months after LASIK, refraction was -1.50 - 0.75 x 105 in the left eye, and uncorrected visual acuity was 20/70, correctable to 20/25 with spectacles.