Tommy C. Y. Chan

One-year outcomes of conventional and accelerated collagen crosslinking in progressive keratoconus

We compared one-year outcomes of conventional (3 mW/cm2, 365-nm ultraviolet-A light, 30 minutes) and accelerated (18 mW/cm2, 365-nm ultraviolet-A light, 5 minutes) collagen crosslinking (CXL) in patients with progressive keratoconus. Main outcome measures were change in keratometry, uncorrected visual acuity (UCVA), and best-corrected visual acuity (BCVA). Nineteen patients in each group completed 1-year follow-up. Preoperatively, there were no inter-group differences for age, keratometry, corneal thickness, and spherical equivalent (p > 0.127). One year postoperatively, maximum and minimum keratometry were flattened by 1.6 diopters (p < 0.023) and 2 diopters (p < 0.047) respectively after conventional CXL, and, 0.47 diopters (p = 0.471) and 0.19 diopters (p = 0.120) respectively after accelerated CXL. Association analysis showed significant negative association between baseline maximum keratometry and change in maximum keratometry after accelerated CXL (p = 0.002) but not after conventional CXL (p = 0.110). Corneal thickness was reduced significantly in both groups (p = 0.017). An improvement in UCVA (p < 0.001) and BCVA (p < 0.022) was noted in both groups along with a reduction in spherical equivalent postoperatively (p < 0.026). There were no inter-group differences for any of the parameters postoperatively (p > 0.184). Although no statistically significant differences were observed between both treatment modalities, a more effective topographic flattening was observed with conventional CXL as compared to accelerated CXL in this study.

Comparison of Outcomes of Primary Anterior Chamber Versus Secondary Scleral-Fixated Intraocular Lens Implantation in Complicated Cataract Surgeries

PURPOSE To compare the outcome of primary anterior chamber vs secondary scleral-fixated intraocular lens (IOL) implantation in complicated cataract surgeries. DESIGN Retrospective, comparative study. METHODS A consecutive series of complicated cataract surgeries with primary anterior chamber (ACIOL) or secondary scleral-fixated IOL implantation from January 1, 2004 to December 31, 2009 was analyzed. Main outcome measures included the postoperative best-corrected visual acuity (BCVA) and postoperative complications. RESULTS There were 89 eyes in the primary ACIOL group and 74 eyes in the secondary scleral-fixated IOL group. The mean follow-up duration was 64.1 ± 36.7 months. The mean postoperative logarithm of minimal angle of resolution (logMAR) BCVA at 1 year was 0.32 ± 0.54 and 0.34 ± 0.21 in the primary ACIOL group and the secondary scleral-fixated IOL group, respectively (P = .734). The mean latest logMAR BCVA was 0.68 ± 0.54 and 0.61 ± 0.47 in the primary ACIOL group and the secondary scleral-fixated IOL group, respectively (P = .336). The primary ACIOL group had more early postoperative complications (P < .001). No difference in late postoperative complications was observed between the 2 groups (P = .100). Regression analysis showed that primary ACIOL and secondary scleral-fixated IOL implantation had similar latest postoperative logMAR BCVA (P = .927), while the presence of late complications was associated with a worse final visual outcome (P = .000). CONCLUSIONS This study shows that there are no long-term differences in the visual outcomes and complication profiles after primary ACIOL or secondary scleral-fixated IOL implantation in a complicated cataract operation when capsular support is inadequate.

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.

Orthokeratology-Associated Infectious Keratitis in a Tertiary Care Eye Hospital in Hong Kong

PURPOSE To analyze cases of orthokeratology-associated infectious keratitis managed in a tertiary care eye hospital in Hong Kong between 2003 and 2013. DESIGN Retrospective study. METHODS Case records of patients with infectious keratitis attributable to orthokeratology contact lenses were analyzed. Data analyzed included clinical features, microbiological evaluation, and treatment outcomes. RESULTS A total of 23 patients were included (16 female, 7 male, mean age: 15.0 ± 4.2 years; range: 9-23 years). All patients were using overnight orthokeratology for an average of 2.7 ± 2.8 years (range: 3 months - 10 years) before the onset of infection. Clinical features included corneal infiltrate (n = 14, 60.9%) and corneal perineuritis (n = 12, 52.2%). Fifteen eyes (65.2%) had a positive microbiological culture obtained from corneal scrapings. The most commonly isolated organism was Pseudomonas aeruginosa (n = 6), followed by coagulase-negative Staphylococcus (n = 5) and Acanthamoeba (n = 3). Five cases of Pseudomonas aeruginosa and 5 cases of Acanthamoeba were identified from contact lenses or contact lens solution. The mean duration from disease onset to remission was 31.9 ± 34.9 days (range: 6-131 days). All patients responded to medical treatment, and no emergency surgical intervention was needed. The best-corrected logMAR visual acuity improved significantly from 0.62 ± 0.51 (20/83 Snellen) to 0.15 ± 0.20 (20/28 Snellen) (Wilcoxon signed rank test, P < .001). CONCLUSIONS Orthokeratology-associated infectious keratitis continues to be a serious problem, especially in regions with high prevalence of myopia. Early clinical and microbiological diagnosis and intensive treatment can improve final visual outcomes.

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.

Different Topographic Response Between Mild to Moderate and Advanced Keratoconus After Accelerated Collagen Cross-linking.

Purpose: To evaluate the clinical and topographic effects after accelerated corneal collagen cross-linking (CXL) in keratoconus. Methods: This was a prospective interventional study in 25 eyes of 24 Asian patients with keratoconus, where 10 eyes in group 1 had mild to moderate keratoconus with the steepest keratometry reading (Kmax) < 58 diopters (D), and 15 eyes in group 2 had advanced keratoconus with Kmax ≥ 58.0 D. The patients underwent accelerated CXL with 18 W/cm2 UV-A light for 5 minutes. Clinical and topographic parameters were obtained before and 1 year after treatment. Results: Overall, spectacle-corrected distance visual acuity, refraction, average keratometry readings, Kmax, anterior elevation at the apex, and corneal endothelial cell density remained stable (P < 0.102). Posterior elevation at the apex increased at 1 year (P = 0.002). The thinnest pachymetry readings also showed significant reduction (P < 0.001). Kmax in group 1 increased by 1.00 ± 1.63 D (range, −2.2 to 5.4 D; P = 0.012), whereas Kmax in group 2 reduced by 1.69 ± 2.61 D (range, −8.4 to 3.2 D; P = 0.013) at 1 year after accelerated CXL. The change in Kmax between the 2 groups was significantly different (P < 0.001). There was no intergroup difference for the change in other parameters. A significant correlation was found between the preoperative Kmax and postoperative change in Kmax at 1 year (r = −0.648; P < 0.001). Conclusions: Accelerated CXL seems to be effective in preventing progression and causing topographic flattening in advanced cases of keratoconus but not as effective in the less progressed counterparts.

Longitudinal evaluation of posterior corneal elevation after laser refractive surgery using swept-source optical coherence tomography.

PURPOSE To investigate the change in posterior corneal elevation up to 1 year after myopic femtosecond-assisted LASIK and photorefractive keratectomy (PRK). DESIGN Prospective, longitudinal, comparative study. PARTICIPANTS Patients undergoing femtosecond-assisted LASIK or PRK. METHODS Corneal imaging was performed using swept-source optical coherence tomography at baseline and at each postoperative follow-up. A 2-way analysis of variance model with repeated measures and a linear mixed effect model were used to compare the differences in posterior corneal elevation between LASIK and PRK at different points after adjusting for the preoperative spherical equivalent (SEQ), central corneal thickness (CCT), thinnest corneal thickness (TCT), residual bed thickness (RST), and ablation depth (AD). MAIN OUTCOME MEASURES The changes in posterior corneal elevation 1 month, 3 months, 6 months, and 12 months after surgery. RESULTS Ninety-eight eyes of 49 patients (mean age 35.2 ± 8.5 years) (62 LASIK, 36 PRK) were included. The mean change in posterior corneal elevation values after LASIK and PRK were 4.88±0.47 μm versus 3.67±0.48 μm (B-1), 2.42±0.56 μm versus 3.00±0.47 μm (B-3), 3.76±0.46 μm versus 2.76±0.46 μm (B-6), and 2.92±0.46 μm versus 2.72±0.46 μm (B-12), respectively. Significant differences in posterior corneal elevation after LASIK were found from month 1, to month 3, to month 6, to month 12 (P ≤ 0.001), whereas posterior corneal elevation did not change significantly from month 3, to month 6, to month 12 (P ≥ 0.373) after PRK. LASIK and PRK eyes showed significant differences at months 3 and 12 (P ≤ 0.023). A similar pattern was observed for the changes in posterior corneal elevation after LASIK and PRK after adjusting for the effect of SEQ, CCT, TCT, RST, and AD. The adjusted forward displacements of the posterior corneal surface were statistically significant throughout the study period after both refractive surgeries (P < 0.05). CONCLUSIONS The findings of our study suggested that there was a mild but significant forward protrusion of the posterior cornea after femtosecond laser-assisted LASIK and PRK. The posterior cornea fluctuated during the first postoperative year after LASIK, whereas it stabilized as early as 3 months after PRK.

Corneal collagen cross-linking for infectious keratitis: an update of clinical studies

Collagen cross‐linking (CXL) with ultraviolet light‐activated riboflavin is a corneal surface procedure developed for the treatment of keratoconus and corneal ectasia. With the known microbicidal and corneal stiffening effects of ultraviolet irradiation and photoactivated riboflavin, it has recently been introduced for the management of infectious keratitis, especially for ulcers resistant to antimicrobial therapy or associated with corneal melting. Various authors have attempted to use CXL as an adjunctive, salvage or even as the sole treatment for infectious corneal ulcers. The aim of this review was to provide a summary of the clinical studies in the literature. It is worth noting that there is still no consensus on the treatment protocol of CXL against infectious keratitis. The disparities in outcome measures, treatment protocol and study design can confound the interpretation and hamper the generalization of the study results. Based on current evidence, the role of CXL in infectious keratitis remained unclear despite the reported success in some clinical cases. Further investigations are warranted concerning the efficacy and safety of treating infectious keratitis with CXL.

Longitudinal Evaluation of Cornea With Swept-Source Optical Coherence Tomography and Scheimpflug Imaging Before and After Lasik.

Abstract Swept-source optical coherence tomography (OCT) is the latest advancement in anterior segment imaging. There are limited data regarding its performance after laser in situ keratomileusis (LASIK). We compared the reliability of swept-source OCT and Scheimpflug imaging for evaluation of corneal parameters in refractive surgery candidates with myopia or myopic astigmatism. Three consecutive measurements were obtained preoperatively and 1 year postoperatively using swept-source OCT and Scheimpflug imaging. The study parameters included central corneal thickness (CCT), thinnest corneal thickness (TCT), keratometry at steep (Ks) and flat (Kf) axes, mean keratometry (Km), and, anterior and posterior best fit spheres (Ant and Post BFS). The main outcome measures included reliability of measurements before and after LASIK was evaluated using intraclass correlation coefficient (ICC) and reproducibility coefficients (RC). Association between the mean value of corneal parameters with age, spherical equivalent (SEQ), and residual bed thickness (RBT) and association of variance heterogeneity of corneal parameters and these covariates were analyzed. Twenty-six right eyes of 26 participants (mean age, 32.7 ± 6.9 yrs; mean SEQ, −6.27 ± 1.67 D) were included. Preoperatively, swept-source OCT demonstrated significantly higher ICC for Ks, CCT, TCT, and Post BFS (P ⩽ 0.016), compared with Scheimpflug imaging. Swept-source OCT demonstrated significantly smaller RC values for CCT, TCT, and Post BFS (P ⩽ 0.001). After LASIK, both devices had significant differences in measurements for all corneal parameters (P ⩽ 0.015). Swept-source OCT demonstrated a significantly higher ICC and smaller RC for all measurements, compared with Scheimpflug imaging (P ⩽ 0.001). Association of variance heterogeneity was only found in pre-LASIK Ant BFS and post-LASIK Post BFS for swept-source OCT, whereas significant association of variance heterogeneity was noted for all measurements except Ks and Km for Scheimpflug imaging. This study reported higher reliability of swept-source OCT for post-LASIK corneal measurements, as compared with Scheimpflug imaging. The reliability of corneal parameters measured with Scheimpflug imaging after LASIK was not consistent across different age, SEQ, and RBT measurements. These factors need to be considered during follow-up and evaluation of post-LASIK patients for further surgical procedures.

Clinical characteristics and surgical outcomes of phacoemulsification in true exfoliation syndrome.

Purpose To review the clinical characteristics and surgical outcomes of patients with true exfoliation syndrome of the lens capsule having phacoemulsification cataract surgery. Setting Hong Kong Eye Hospital, Kowloon, Hong Kong. Design Case series. Methods Eyes of patients with true exfoliation syndrome diagnosed clinically or intraoperatively had standard phacoemulsification and intraocular lens (IOL) implantation. The anterior capsules removed during capsulorhexis were sent for histological confirmation. Results Twenty‐four eyes of 18 patients were included. All eyes were confirmed to have true exfoliation syndrome by histological examination of the anterior lens capsule. Seven eyes (29.2%) had preexisting chronic glaucoma; 5 (20.8%) had laser iridotomy before the diagnosis. During phacoemulsification, all eyes had a continuous curvilinear capsulorhexis without complications. Trypan blue staining was used during capsulorhexis in 11 eyes (45.8%). Posterior capsule rupture occurred during lens chopping in 1 eye (4.2%). No loose zonular fibers or radial extension of capsulorhexis occurred. Capsular bag IOL implantation was successfully performed in all cases except the 1 with a posterior capsule rupture, in which an anterior chamber IOL was implanted. Conclusions Phacoemulsification was safely performed in eyes with true exfoliation syndrome. Trypan blue staining can be used to facilitate capsulorhexis creation. Ultrasound biomicroscopy or anterior segment optical coherence tomography may be useful in preoperative assessment of such cases. The disease may be associated with glaucoma and laser iridotomy. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.