Marion H. Edwards

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.

Prevalence of myopia in local and international schools in Hong Kong.

Purpose. This study aims to investigate genetic and environmental influences on physiological myopia by studying the difference in myopia prevalence between local schools and international schools in Hong Kong. Methods. Vision screening was carried out in local and international schools for students 13 to 15 years old. Types of refractive error were identified by visual acuity measurement, the presence of spectacles, a simple refraction, and the use of plus and minus ophthalmic lenses. Results. Three local schools and six international schools participated in the study. Two hundred eighty-nine students were from the local schools, and 789 students were from the international schools. Prevalence of myopia at the local schools ranged from 85 to 88%, whereas it ranged from 60 to 66% in the international schools. Students in the international schools were subdivided into Chinese origin, white, mixed Chinese, and Asian. Prevalence of myopia was highest in the Chinese group (82.8%) and lowest in the white group (40.5%). There was no age or gender difference in the prevalence of myopia. Conclusions. Hong Kong Chinese students had a higher prevalence of myopia regardless of whether they studied in local or international schools when compared with other ethnic groups, such as whites. This further supports a genetic input into myopia development.

A 2-year longitudinal study of myopia progression and optical component changes among Hong Kong schoolchildren.

This study investigated refractive error and optical component changes in a group of 142 Hong Kong schoolchildren from age 6 to 17 years over a 2-year period between 1991 and 1993. Subjects were refracted subjectively and corneal curvatures and ocular dimensions were measured. At the end of the 2-year study, the mean spherical equivalent refraction (SER) was -1.86 D (SD 1.99 D) and 62% of the schoolchildren were myopic. The annual incidence of myopia was 11.8%. Children aged 10 years and under had a greater change in SER toward myopia than older children. The annual rate of myopia progression for the myopic children was -0.46 D (SD 0.40 D) and the rate of progression was greatest between age 6 and 10 years old. Vitreous depth/axial length elongation was the main component contributing to the progression of myopia. Hong Kong schoolchildren develop myopia as early as 6 years old and myopia progresses at a greater rate compared with children of European extraction.

The development of myopia in Hong kong children between the ages of 7 and 12 years : a five-year longitudinal study

The purpose of this work was to characterize the development of refractive error in Hong Kong children between the ages of 7 and 12 years. A non self‐selected sample of 7‐year old children was recruited and followed for 5 years, non‐cycloplegic refractions being carried out annually. A life‐table was used to determine myopia incidence and prevalence. The mean annual change in the spherical equivalent refraction (SER) was −0.32 D; 75 out of 83 subjects followed for 5 years became less hyperopic or more myopic, the maximum progression occurring between 9 and 11 years of age. The mean change in SER over the 5 years in children who were myopic at age 12 years was significantly greater than that in children who remained non‐myopic. The incidence of myopia at age 7–8 years was 9% and at age 11–12 years was 18–20%. At age 7 years the prevalence of progressive myopia was 1.6% and 2.5% of subjects had anisometropia. Any treatment to prevent myopia should start by the age of 6 years and treatment to retard development should commence before age 9 years.

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.

The refractive status of Hong Kong Chinese infants

One hundred and fifty‐eight full‐term Hong Kong Chinese infants were examined, at the age of approximately 10 weeks, using retinoscopy. Fifty of the subjects were re‐examined at the ages of 20, 30 and 40 weeks. Cyclopentolate 1% was used to produce cycloplegia. Photographic methods were used to assess the straightness of the eyes of 122 infants. While the mean spherical equivalent of the refractive error at 10 weeks was within the limits reported in studies of Caucasian infants, a rapid decrease, not previously reported, occurred between the ages of 10 and 40 weeks. The amounts of astigmatism found were in line with results from Caucasian eyes but the direction was overwhelmingly with‐the‐rule. The prevalence of anisometropia decreased with age and anisometropia was not prevalent at the age of 37 weeks. Two exotropes (1.6%)and no esotropes were identified although this may have been confounded by the use of cyclopentolate.

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.

Refractive errors in Hong Kong Chinese pre-school children

ABSTRACT Five hundred and seventy Chinese children aged between 36 and 65 months were recruited for refractive examination. The results show that both the spherical and cylindrical components of the refractive error tend to decrease with increasing age, although the changes were not statistically significant. The results of the present study, together with those of earlier studies carried out on Hong Kong Chinese children of different ages, show a pattern in the change of refractive errors in local children during the first 17 years of life. The combined results show that the average spherical refractive error decreases rapidly in hyperopic power during the 1st and the 6th to the 10th years of life; the astigmatic power decreases rapidly in the 1st year of life and remains thereafter rather constant until the age of 17 years.