Sin Wan Cheung

The Longitudinal Orthokeratology Research in Children (LORIC) in Hong Kong: A Pilot Study on Refractive Changes and Myopic Control

Purpose: Myopia is a common ocular disorder, and progression of myopia in children is of increasing concern. Modern overnight orthokeratology (ortho-k) is effective for myopic reduction and has been claimed to be effective in slowing the progression of myopia (myopic control) in children, although scientific evidence for this has been lacking. This 2 year pilot study was conducted to determine whether ortho-k can effectively reduce and control myopia in children. Methods: We monitored the growth of axial length (AL) and vitreous chamber depth (VCD) in 35 children (7–12 years of age), undergoing ortho-k treatment and compared the rates of change with 35 children wearing single-vision spectacles from an earlier study (control). For the ortho-k subjects, we also determined the changes in corneal curvature and the relationships with changes of refractive errors, AL and VCD. Results: The baseline spherical equivalent refractive errors (SER), the AL, and VCD of the ortho-k and control subjects were not statistically different. All the ortho-k subjects found post-ortho-k unaided vision acceptable in the daytime. The residual SER at the end of the study was –0.18 ± 0.69 D (dioptre) and the reduction (less myopic) in SER was 2.09 ± 1.34 D (all values are mean ± SD). At the end of 24 months, the increases in AL were 0.29 ± 0.27 mm and 0.54 ± 0.27 mm for the ortho-k and control groups, respectively (unpaired t test; p = 0.012); the increases in VCD were 0.23 ± 0.25 mm and 0.48 ± 0.26 mm for the ortho-k and control groups, respectively (p = 0.005). There was significant initial corneal flattening in the ortho-k group but no significant relationships were found between changes in corneal power and changes in AL and VCD. Conclusion: Ortho-k can have both a corrective and preventive/control effect in childhood myopia. However, there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects.

Orthokeratology practice in children in a university clinic in Hong Kong

Purposes:  The aim of this study was to analyse clinical data of children undergoing orthokeratology (ortho‐k) and to investigate patients’/parents’ perspective on ortho‐k via telephone interviews.

Repeatability of corneal thickness measurements made by a scanning slit topography system

Two sets of corneal thickness (CT) measurements at five corneal locations were made with Orbscan on 33 normal young adults. No significant intravisit and intervisit differences at any of the corneal locations were found (Repeated measures anova, F < 0.49, p > 0.49). The 95% limits of agreement (95% LA) for between‐measurement differences for the central cornea was about ±19 μm (or 3%), indicating good repeatability; for the inferior, temporal and nasal corneal locations, the 95% LA were close to ±30 μm (≈4–5%); and for the superior corneal location, they were about ±35 μm (or 5.5%). The estimated number of repeated measurements that should be taken for accurate CT measurements (at any of the five corneal locations and excluding outliers of >3 S.D.) of 2% (standard error) is ≤2, and of 3% is 1. This study shows that only central CT measurements with the Orbscan are repeatable. The role of the Orbscan pachometry is therefore limited and is recommended for central CT measurements only.

Practice of orthokeratology by a group of contact lens practitioners in Hong Kong

Purpose: The aim of the study was to provide information about the characteristics of three main types of orthokeratology (ortho‐k) lenses used in Hong Kong and to report on their performance based on the clinical impressions of a group of ortho‐k practitioners.

An assessment of consecutively presenting orthokeratology patients in a Hong Kong based private practice

Purpose: The aim of this study was to collect objective, subjective and demographic data on consecutively presenting orthokeratology (ortho‐k) patients who attended for routine followup examination in a Hong Kong based private practice in May 2001.

Practice of orthokeratology by a group of contact lens practitioners in Hong Kong--Part 1. General overview.

Purpose: To describe orthokeratology (ortho‐k) as practised by a number of practitioners in Hong Kong.

Effect of cycloplegia on axial length and anterior chamber depth measurements in children

Background:  Cycloplegia has been shown to have no effect on axial length measurement made with the IOLMaster in adults. The current study aimed at evaluating the effect of cycloplegia on axial length and anterior chamber depth (ACD) measurements made with the IOLMaster and an ultrasonic biometer in children.

Refractive Error and Visual Acuity Changes in Orthokeratology Patients

Purpose. To evaluate the refractive error and visual acuity (VA) at various contrast levels in the two eyes of overnight orthokeratology (ortho-k) subjects, and to compare their postortho-k VA with the best corrected VA of spectacle-wearing control subjects matched for age, gender, and initial refractive error. Methods. Distance postortho-k uncorrected and best corrected logMAR VA at four different contrast levels of 31 ortho-k (test) subjects (aged 7–35 years old) and the best corrected VA of 31 spectacle-wearing (control) subjects were measured and compared using the Waterloo Four-Contrast LogMAR VA Chart, which incorporated four sets of letters at different contrast levels: 90%, 48%, 21%, and 7%. Noncycloplegic manifest refractive error was measured in both eyes. Results. The mean ± SD percentage reductions in spherical equivalent achieved in the current study were 92% ± 11% in the better eye and 84% ± 14% in the worse eye of the test subjects. Postortho-k uncorrected VAs were significantly correlated with the residual overall blurring strength (length of the vector representing the residual refractive error) in both eyes at all contrast levels. The mean postortho-k uncorrected VA in the better eye were 0.00 ± 0.11, 0.08 ± 0.11, 0.21 ± 0.12, and 0.46 ± 0.13 with the 90%, 48%, 21%, and 7% contrast charts, respectively. These were comparable to the best corrected VA of the better eye of the control group with the 90% (–0.03 ± 0.07) and 48% contrast charts (0.03 ± 0.09), but worse than those of the control group with the 21% (0.13 ± 0.10) and 7% (0.35 ± 0.13) contrast charts. Postortho-k VA, with the four different contrast charts, improved by 0.07 to 0.12 log units in the better eye and 0.15 to 0.18 log units in the worse eye after correction of the residual refractive error; the improved VA was comparable to the best corrected VA of the control group. Conclusions. Postortho-k visual outcomes were compromised primarily due to the presence of residual refractive error. Although the uncorrected postortho-k VA was comparable to the best corrected VA of the spectacle wearers at high-contrast levels, it was worse at low-contrast levels and caused a significant between-eye difference at all contrast levels. Therefore, we suggested that monocular VA at high- and low-contrast levels should be evaluated for ortho-k patients.

Repeatability and agreement of two A‐scan ultrasonic biometers and IOLMaster in non‐orthokeratology subjects and post‐orthokeratology children

Purpose:  Our aim was to determine the repeatability of measurements of axial length (AL) and anterior chamber depth (ACD) made with two ultrasonic biometers and the IOLMaster in a group of non‐orthokeratology (ortho‐k) adult subjects and to investigate the agreement among instruments in children undergoing ortho‐k therapy and in children wearing spectacles.

Practitioners’ analysis of contact lens practice in Hong Kong

BACKGROUND The aims of this survey were to appraise contact lens practice and care systems used in Hong Kong between March 2007 and February 2008, and to evaluate the attitude of practitioners towards prescribing different types of contact lenses. METHODS Questionnaires were sent out to 797 optometrists licensed to fit contact lenses in Hong Kong in March 2008. RESULTS The response rate was 27%. About 20% of contact lens patients (as reported by the respondents) were new wearers. Over 90% of contact lens patients were wearing soft contact lenses. Among soft contact lenses, the use of daily disposable and silicone hydrogel lenses had increased from 27% and 3% in 2002 to 37% and 21% in 2008, respectively. Less than 10% were rigid contact lens wearers. For astigmats fitted with soft lenses, only about 46% were fitted with toric lenses. For presbyopes using contact lenses, the majority (57%) were fitted with single vision lenses with over-spectacles, followed by monovision (29%). The most commonly recommended soft lens disinfecting system was multipurpose solution (74%). Less than 20% of the respondents reported confidence in prescribing orthokeratology lenses. CONCLUSION Soft contact lenses continued to dominate the contact lens market in Hong Kong, with silicone hydrogel and daily disposable lenses becoming increasingly popular. The use of toric and bifocal lenses was still not popular among practitioners. Multipurpose solutions were still the care systems of choice by practitioners in Hong Kong.