Population based cataract epidemiological surveys utilising a photodocumentation system

Prevalence of visual impairment in the adult Japanese population by cause and severity and future projections

PURPOSE

To present a comprehensive estimate of the total number of people with visual impairment in the adult Japanese population by age, gender, severity and cause, and to estimate future prevalence based on population projections and expected demographic changes.

METHODS

Definitions of visual impairment used in this study were based on the United States criteria. Total visual impairment was calculated as the sum of low vision and blindness. The prevalence estimates were based on input from a number of Japanese epidemiological surveys, census material and official population projections.

RESULTS

There were an estimated 1.64 million people with visual impairment in 2007 in Japan. Of these, 187,800 were estimated to be blind. The prevalence of visual impairment in Japan increased with age and half of the people with visual impairment were aged 70 years or older. The leading causes of visual impairment in Japan were glaucoma (24.3%), diabetic retinopathy (20.6%), degenerative myopia (12.2%), age-related macular degeneration (10.9%), and cataract (7.2%). These five major causes comprised three-quarters of all visual impairment. The prevalence of visual impairment was projected to increase from 1.3% of the population in 2007 to 2.0% by 2050.

CONCLUSIONS

This comprehensive study presents the prevalence of total visual impairment in the adult Japanese population. The projected increases in the prevalence of visual impairment over time reflect the demographic changes of a declining and aging Japanese population. These projections highlight that the burden of disease due to visual impairment and imposed on society is likely to increase.

Prevalence of cataract in rural Indonesia

PURPOSE

To describe the prevalence of cataract in adults in rural Sumatra, Indonesia.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

A random sample of all adults aged 21 years or older living in 3 rural villages in central Sumatra was assessed. Nine hundred nineteen of 1089 (84.4%) eligible adults participated.

METHODS

A team of 7 ophthalmologists examined the anterior segment of both eyes using a portable slit lamp after pupil dilatation. Lens opacity was graded according to the Lens Opacities Classification System III (LOCS III). A structured questionnaire was used to collect data on education level and income.

MAIN OUTCOME MEASURES

Cataract was defined as either a LOCS III nuclear region score of > or =4.0, cortical > or =4.0, or posterior subcapsular (PSC) cataract > or =2.0, in either eye.

RESULTS

Two hundred one (21.9%) of 919 subjects were found to have cataract. The age-adjusted prevalence rate of cataract (including cataract surgery) was 23.0% (95% confidence interval, 20.8-25.2). The most common type of cataract for both genders (adjusted for age) was mixed (13%) followed by nuclear only (5.7%), and cortical only (4%). The prevalence rate of any cataract for adults aged 21 to 29 was 1.1%, increasing to 82.8% for those aged older than 60 years. Similar trends with age were noted for nuclear, cortical, and PSC cataract. Women had higher prevalence rates than men for all types of cataract except cortical. There was a trend of increasing prevalence of all types of cataract with decreasing education (P<0.001).

CONCLUSIONS

Cataract prevalence in adults aged 21 years and older in rural Indonesia is among the highest reported in Southeast Asia. Despite this, there are inadequate resources available to manage this treatable disease. Allocation of resources to tackle the present burden of cataract would likely have large personal, social, and economic benefits.

UV-B and early cortical and nuclear changes in the human lens

Experimental studies in mice and rats have shown that UV (B) irradiation leads to specific lens changes, viz. yellowing of the nucleus and a multilayered epithelium in the anterior pole with disrupted cortical fibres underneath. Biomicroscopic and ultrastructural studies on ageing human lenses revealed yellowing of the lens nucleus and locally ruptured membranes and small opacities in the equatorial cortex. No changes in the anterior pole were ever observed. This discrepancy between the human and animal lens, contraindicating UV as an important risk factor for human cataract, is discussed and may be due to several factors: (1) a difference between the high level acute and low level chronic irradiation; (2) species differences: nocturnal animals may be unable to cope with bright light exposure; (3) differences in scavenger and other defense mechanisms between humans and animals.

Cataract classification

Opacifications of the eye lens--generally defined as cataracts--develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of 'cataract formation' cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The 'objective methods' for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lens before visible (and therefore subjectively recognizable) opacifications occurred. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.