Orbital development in Hong Kong Chinese subjects

The purpose of this study was to examine the development of the orbit in Hong Kong Chinese subjects. Orbit volume was determined from magnetic resonance images of 81 subjects aged from 1 to 42 years old. Results show that orbit volume ranged from 11.56 to 25.50 cm3. In the first year of life, the mean orbit volume was 12.36 cm3. The orbit showed rapid growth in the first 3 years of life. From about 1-3 years old, the mean volume was 15.31 cm3. The orbit grew steadily to the age of 10 years. From age 11 to 15 years old, the mean volume was 20.24 cm3. Orbit growth levelled off at about 16 years of age with the mean volume at 21.00 cm3.     

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.     

Nearwork-induced transient myopia in preadolescent Hong Kong Chinese

PURPOSE: To compare the magnitude and time course of nearwork-induced transient myopia (NITM) in preadolescent Hong Kong Chinese myopes and emmetropes. METHOD: Forty-five Hong Kong Chinese children, 35 myopes and 10 emmetropes aged 6 to 12 years (median, 7.5), monocularly viewed a letter target through a Badal lens for 5 minutes at either 5.00- or 2.50-D accommodative demand, followed by 3 minutes of viewing the equivalent target at optical infinity. Accommodative responses were measured continuously with a modified, infrared, objective open-field autorefractor. Accommodative responses were also measured for a countercondition: viewing of a letter target for 5 minutes at optical infinity, followed by 3 minutes of viewing the target at a 5.00-D accommodative demand. The results were compared with tonic accommodation and both subject and family history of refractive error. RESULTS: Retinal-blur-driven NITM was significantly greater in Hong Kong Chinese children with myopic vision than in the emmetropes after both near tasks, but showed no significant dose effect. The NITM was still evident 3 minutes after viewing the 5.00-D near task for 5 minutes. The magnitude of NITM correlated with the accommodative drift after viewing a distant target for more than 4 minutes, but was unrelated to the subjects' or family history of refractive error. CONCLUSIONS: In a preadolescent ethnic population with known predisposition to myopia, there is a significant posttask blur-driven accommodative NITM, which is sustained for longer than has previously been found in white adults.     

Analysis of refractive status of Hong Kong Chinese infants

Recently developed methods of quantifying changing dioptric power are applied to the refractive status of Hong Kong Chinese infants from about 10 to about 40 weeks of age. The analysis confirms that hyperopia decreases during the period and that with-the-rule astigmatism predominates. Change, however, is not constant over the period. The rate of decrease of hyperopia slows down and the refractive status becomes more spherical. The mean refractive status is calculated at 10, 20, 30 and 40 weeks. The spread of refractive status is represented by variance-covariance matrices calculated for each group and 95% confidence ellipsoids on the mean are constructed. The variance-covariance exhibits little change over the period. The right and left eyes show similar behaviour.     

Refraction referral criteria for Hong Kong Chinese preschool children

The major types of ametropia and visual problems for Hong Kong Chinese and Caucasian children are different. Consequently, the referral criteria developed for Caucasian children may not be applicable to Hong Kong children. Results of our study suggested that the referral criteria for Hong Kong children should be set as hyperopia of ≥+ 2.0 D, myopia of ≥ 1.0 D, anisometropis of ≥ 1.0 D and anisometropia of ≥ 1.25 D. Sensitivity using only these criteria for abnormal refraction in identifying children with amblyopia. Esotropia, exotropia and subnormal vision (< 6/12) was respectively 100%, 84.6%, 45.2% and 95.7%. The overall sensitivity for the identification of visual problems was 86.1 % and the overall specificity was 76%. If a cover test or a Hirschberg test was introduced into the screening battery so that all the strabismic cases were identified, the overall sensitivity would increase to 98.6%.     

Incidence of diabetic retinopathy in a Hong Kong Chinese population

Background: The aim was to examine the progression and regression of diabetic retinopathy within a four‐year period in a Chinese population with type 2 diabetes mellitus in a community optometry clinic in Hong Kong. Methods: During the period May 2005 to November 2009, 5,160 patients with type 2 diabetes mellitus who had attended at least two diabetic retinopathy screening sessions at a community optometry clinic were included as subjects in this study. All had retinal photographs taken of both eyes, which were of sufficiently good quality for grading. For the purpose of this study, diabetic retinopathy grading was based on the results of the worst eye. The main outcomes were the within four‐year incidence of diabetic retinopathy and the incidence of progression and regression of diabetic retinopathy. Results: Of the 5,160 subjects in this study, 3,647 had no diabetic retinopathy, while 1,513 had diabetic retinopathy at the baseline visit. Of those 3,647 subjects with no diabetic retinopathy, the within four‐year cumulative incidence of any diabetic retinopathy, mild or moderate non‐proliferative diabetic retinopathy and sight‐threatening diabetic retinopathy was 15.16 per cent, 14.45 per cent, 0.69 per cent and 0.03 per cent, respectively. Of those 1,513 subjects with diabetic retinopathy at baseline, the within four‐year progression incidence of diabetic retinopathy was 6.61 per cent and the regression incidence of diabetic retinopathy was 45.54 per cent. Conclusion: The high regression incidence of diabetic retinopathy suggests that it might not be necessary for all patients with diabetes to be screened annually. Other methods to determine the screening frequency for an individual patient should be explored.     

Autosomal recessive inheritance of myopia in Hong Kong Chinese infants

Hong Kong Chinese infants were refracted by retinoscopy at regular intervals between the age of approximately 10 and 40 weeks. Cyclopentolate 1% was used to obtain cycloplegia. The spherical equivalent of the refractive error was calculated for each child and analysis of variance carried out according to the refractive status of the parents. From approximately 20 weeks of age a significant difference was found between the mean spherical equivalent of the refractive error of infants of parents both of whom were myopic and that of infants of parents neither of whom was myopic. At 40 weeks of age a good fit with an autosomal recessive probability model was obtained.     

Effect of parental myopia on the development of myopia in Hong Kong Chinese

A representative sample of Hong Kong Chinese children was followed from 7 to 12 years of age. Refractive error was measured every year (n = 123 at age 7 years and n = 83 at age 12 years), the axial length of the eye was measured at age 12 years (n = 81) and the refractive status of the parents was also determined. Thirty-one percent of the parents in the sample were myopic and at the age of 12 years 53% of the children were myopic. There was no association between the refractive status of the parents and whether or not a child had myopia. The probability of a 12-year-old child with early-onset myopia having at least one myopic parent was 0.55 and the probability of myopic parents having a myopic child was 0.6. There was no difference in the refractive error or the axial length of 12-year-old children according to whether neither, one or both parents were myopic. The genetic influence on myopia may be different in Caucasian and Chinese children, although it is also possible that non-expression of the genotype in the parents may have confounded the determination of the inheritance pattern of myopia in Hong Kong Chinese children.     

Normal values of eye position in the Chinese population of Hong Kong.

Exophthalmos, interpupillary distance (IPD), interobital distance (IOD), and inner intercanthal distance (ICD) were measured in an adult Chinese population from Hong Kong (HKC). Mean values and normal range for 95% of the population were determined and the relation with head size and body height examined. Values of exophthalmos and IPD in our Chinese population were similar to those given for Caucasian groups. IOD and ICD were larger in the Chinese than in adult Caucasians. Our findings show generally larger values in the HKC than has been found for other populations in mainland China.     

Inter- and intra-individual variability of non-invasive tear break-up time in Hong Kong Chinese

Non-invasive tear break-up time (NITBUT) has been proposed as a measure of tear film integrity which is superior to the more commonly used tear break-up time (TBUT), since it does not alter the volume or the physicochemical properties of the tear layer by the addition of fluorescein. We measured NITBUT by measuring the time taken for distortions or discontinuities to appear in the reflected image of a grid pattern which covered about 80 per cent of the corneal surface. NITBUT measures were made 100 times on seven Hong Kong Chinese subjects with up to 20 consecutive measures being made on a single day. We also measured NITBUT on one occasion on an unselected population of 52 Hong Kong Chinese subjects. NITBUT shows a skewed distribution in all subjects, with many shorter values and some extremely long values. There are statistically significant variations in NITBUT from day to day, and from subject to subject. The group of 52 subjects also had a skewed NITBUT distribution with many short values and some very long values. The arithmetic mean does not adequately represent NITBUT data, either for individual subjects or for this group of subjects. As many as five to eight measures may be necessary to gain a stable estimate of the NITBUT and stability of the measure is improved if extreme values are omitted. We recommend the use of nonparametric statistics to compare NITBUT values from day to day in or between subjects.