THE HONG KONG VISION STUDY: A PILOT ASSESSMENT OF VISUAL IMPAIRMENT IN ADULTS* BY Mylan R. Van Newkirk, MD MPH ABSTRACT Purpose: The Hong Kong Adult Vision Pilot Study is a population based study ofthe distribution and determinants ofeye disease in a random sam- ple of the Chinese population age 40 and over. The present pilot study identifies the extent and causes of visual loss using methods developed in the United States and Australia. The pilot study uses the prevalence data to estimate the sample size necessary to predict the size of an effect a larg- er study may detect and the confidence with which that effect may be con- sidered and the standard deviation of the Hong Kong population. The smallest detectable odds ratios were calculated based on known risk factor prevalence rates of the pilot study. Methods: Hong Kong Chinese residents aged 40 and over in 2 random cluster sites were identified by private household census. The examina- tions were performed at one location and included, health history and habits, presenting and best corrected LogMar vision, Humphrey visual field and IOP measurement, dilated slit lamp, fundus examination, fundus photography and echography. Results: In the two test sites, 355 people were examined of the 441 eli- gible residents (81% response). 76.6% of the population reported a change in vision in the last 10 years; 45% had not sought examination. 4.54% had vision less than 20/60. This was caused by: myopic choroidal degeneration (31%), cataract (19%), cataract + ARM (19%), ARMD (19%), glaucoma (6%), and corneal disease (6%). Vision loss increased sig- nificantly with age. Vision loss was more common in older women than in older men. *Supported by Orbis International, New York, NY; the University of Melbourne Collaborative Research Program, Melbourne, Australia; the Hong Kong Polytechnic University Research Committee, Hong Kong; the Chinese University Student Work Scheme, Hong Kong; Carl Zeiss Inc., Hong Kong; Kodak (Far East) Ltd, Hong Kong; and Alcon Laboratories, Ft. Worth, TX. TR. AM. OPHTH. SOC. VOL. XCV, 1997 716 Van Newkirk The prevalence rates calculated from the pilot study data were used, requiring a relative precision of 95% and ±20% confidence interval of the prevalence rates, indicate that a sample size of2500 would be a good num- ber for a larger study. Conclusions: The methods developed in the United States and Australia for completing eye disease prevalence studies are applicable in Hong Kong. Vision loss is increasingly common in older people and the percent of visual impairment in Hong Kong is higher than studies in the US and Australia. As the population ages demands on the health care systems will increase. The results from this pilot warrant continuation of the study. Efforts must be directed toward prevention of visual loss. INTRODUCTION The Hong Kong Vision Study (HKVS) was developed to collect data that would assist in the appropriate design ofa larger study in Hong Kong. The information collected would be comparable to studies completed in the United States and Australia. These investigations have been greatly enhanced by the development of a comprehensive methodology.'l Well- designed population-based studies are the best source of valid and reli- able information regarding disorders of the eye. Such data are of great importance in (1) defining the distribution and prevalence of eye diseases, (2) investigating etiologies and risk factors, (3) planning appropriate eye health care services, (4) developing prevention and rehabilitation pro- grams, and (5) projecting costs of all these activities. VISUAL IMPAIRMENT Estimates of world blindness are hindered by inadequate data and by incomparability because of differences in survey methodology and defini- tions. The prevalence of blindness is estimated at between 38 and 40 mil- lion people worldwide, with 65% of those affected living in Asia.67 Blindness is more prevalent in the older ages.", 1-10 Life expectancy in Hong Kong is greater than that in the United States, Russia, Germany, and all of Asia except Japan."1 Accessibility, utilization, and quality of eye care services affect eye disease prevalence data in communities, especially in the area ofpreventable blindness caused by cataract, diabetic retinopathy, and glaucoma.'2 In combination with these health care delivery issues, environmental and geographic factors influence infectious and nutritional causes ofblindness, such as onchocerciasis, trachoma, and vitamin A defi- ciency, which are significant causes ofblindness in some parts ofthe world. Visual Impairment in Adults 717 Cataract Cataract, the most common cause of blindness worldwide, accounts for nearly 50% of all blindness.13 The World Health Organization (WHO) estimates that halfofthe 60-year-old population and all ofthe 80-year-old population have some form of lens opacity.'4 Cataract is a major public health problem for the aging population of Hong Kong.'5 While Hong Kong is a highly developed economic machine and the public health sys- tem possesses the latest technologic equipment, efficiency and productiv- ity in cataract surgical management have not been implemented. In spite of a recent increase in cataract surgery, the waiting period for cataract surgery may be more than 2 years in the public hospital system there. Cataract is the major reason for eye surgery in the world; although surgery is very effective in restoring vision, it is a major worldwide health care expense. Important risk factors, including exposure to solar radiation (UV-B), smoking, heavy consumption of alcoholic beverages, diabetes mellitus, and drug toxicity (eg, from corticosteroids), have been linked to cataract."' The prevalence of cataract doubles with every decade of life over 40 years of age.Y' With the aging population, it is extremely impor- tant to identify ways to prevent or delay cataract. A 10-year delay in the development of cataract would reduce the number of cataract operations needed by 45%.25 Glaucoma Worldwide, glaucoma is the third leading cause of blindness in the elder- ly. It is estimated that 10% of blindness in Asia is the result of all types of glaucoma.7 The majority ofpeople with open-angle glaucoma (OAG) are asymptomatic until the late stages of the disease, when visual field loss is already significant.26 Angle-closure glaucoma (ACG) is very common in Asia and is three times more prevalent than OAG in Taiwan.27 Ethnic and genetic factors of glaucoma are poorly understood. However, OAG is more prevalent in blacks than in whites, and age at onset is younger in the black populations of East Baltimore and Barbados than in their white pop- ulations."3 In a registration ofpermanent blindness in Hong Kong, glau- coma is ranked as the third-leading cause of blindness seen at the Hong Kong Eye Hospital and Tung Wah Eastern Hospital in 1994."5 Diagnosis of glaucoma requires detailed assessment of the optic disc and peripheral visual function. When glaucoma diagnostic assessment is properly imple- mented in prevalence studies, only about half of participants with glauco- ma are found to have been previously diagnosed.3' The methodology required may be perceived as too complex and time-consuming for inves- tigators and participants, but it must be performed to obtain an accurate picture of glaucoma.34 718 Van Newkirk Diabetic Retinopathy Diabetic retinopathy is the most common cause of new cases ofblindness among people ofworking age in the developed world.3536 The most signif- icant predictive factor for diabetic retinopathy has been duration of the disease; however, the recent report of the Diabetes Control and Complications Trial37 has shown that intensive control of diabetes can retard the progression of diabetic retinopathy. Elevated glycated hemo- globin levels measured at baseline in the Wisconsin Epidemiological Study of Diabetic Retinopathy in insulin-dependent and non-insulin-dependent diabetic participants are associated significantly with a progression of retinopathy, progression to proliferative diabetic retinopathy, and an increase in macular edema at the 10-year follow-up examination. Low, near-normal levels of glycated hemoglobin appear protective in patients with insulin-dependent and non-insulin-dependent diabetes mellitus.38 A recent vision survey in Melbourne, Australia, reveals that fewer than 50% ofthe people with diabetes are receiving timely and appropriate eye exam- inations.39 In Hong Kong, only 38% of diabetic subjects working in an industrial company were found to have been previously diagnosed with diabetes.40 The prevalence of diabetes mellitus in Asia is projected to increase from 51.4 million in 1994 to 138.2 million by 2010.41 An esti- mated 95% of visual loss from diabetic retinopathy could be prevented with improved management ofdiabetes and early detection and treatment of diabetic retinopathy.4243 Age-Related Maculopathy ARM is the major cause of visual impairment in the United States, the United Kingdom, and Australia and is more prevalent in the older age- groups.'5' 4'4 In Australia, late ARM or age-related macular degeneration (ARMD) accounts for 27% ofvisual impairment in the Melbourne Visual Impairment Project and for 88% in the Blue Mountains Eye Study.41'46 The pathogenesis of ARMD and the relationship of soft or reticular drusen, retinal pigment epithelium, and neuroepithelium to atrophy and choroidal neovascularization is described by Gass.47 Blindness in ARM is due primarily to dry ARMD or geographic atrophy of the retinal pigment epithelium (80%) and less commonly to the neovascular form (20%) of ARM.48 ARM is much less common in blacks.49 ARM is a poorly defined cause of blindness in the Chinese population, but the prevalence appears to be much lower than in whites. However, registration of permanent blindness ranks macular degeneration as second only to cataract as a lead- ing cause ofblindness seen at the Hong Kong Eye Hospital and Tung Wah Eastern Hospital in 1994.'5 Visual Impairment in Adults 719 Myopia and Myopic Choroidal Degeneration Myopia is an important risk factor for several eye diseases.