Angle closure in the developing world: what does the future hold?

Angle closure disease is a significant health problem in Asia with the majority of disease being reported from developing countries. In India alone, an estimated 27.6 million persons currently have some form of angle closure disease. With relatively young populations and improving life expectancy, this could result in a huge increase in numbers of affected people over the next few decades. Biometric risk factors for angle closure have included axial length, anterior chamber depth and lens thickness. A shorter axial length is a consistent risk factor for angle closure disease possibly because of the associated crowding of the anterior segment. Central anterior chamber depth again appears to confer significant risk for angle closure disease, as it influences angle recess width. The relationship of lens thickness with risk of angle closure is less clear. Some reports do find an association with angle closure disease, whereas others do not. This is surprising because the position and thickness of the crystalline lens would be expected to be intimately related with angle recess width with the possible exception of plateau iris syndrome. These inconsistencies could at least partly be explained by the difficulty in keeping accommodation constant while measuring lens thickness. Because lens thickness changes with changing accommodation, controlling for this while measuring biometric parameters is essential and challenging. Specific details as to whether a technique was used that controlled accommodation is lacking from most reports on biometry in angle closure disease. The other question that arises with this dynamic measure is whether the lens thickness measured is actually the thickest and most anterior lens position for that eye that would be the setting for the narrowest angle recess. This is even more relevant with the recent description of the lens vault as a risk factor for angle closure disease. The dynamic range of values for accommodation and lens thickness and their influence on angle recess width in large population sets is lacking. The older population at risk for angle closure disease also has cataractous lens changes and presbyopic changes, both of which influence lens thickness and plasticity. Population-based studies have reported other associations with ocular biometric parameters. The relationship between height and axial length has been consistent across different populations. Jonas et al. in this issue report that lens thickness is directly correlated, whereas anterior chamber depth has an inverse relationship with increasing height. This relationship was independent of axial length. Their study population from the Central India Eye and Medical Study lives in a rural setting that has not undergone marked changes in their native environment and lifestyle. Wong et al. from an urban population in Singapore report that increasing axial length was associated with more years of education, more near work and higher income. Jonas et al.’s study is from a population in Central India’s rural setting that has not undergone marked changes in their native environment and living style. The relationship between ocular biometry and height has implications for angle closure disease in the developing world. Increased height is associated with improved incomes and nutrition. In developing countries with high growth rates, health indices are rapidly changing. Increased emphasis on education could also mean increased hours of near work which is an independent association for a longer axial length. Indirect evidence of changes in axial length with development is seen. Vijaya et al. report angle closure prevalence from The Chennai Glaucoma Study in South India. The normal cohort in the urban population had a 0.35 mm longer eye than the rural cohort with similar anterior chamber depths. Both populations had a similar prevalence of angle closure glaucoma. Will these influences on axial length translate into lower risk of angle closure disease over time? Jonas et al. also report a decrease in lens thickness seen in the oldest two age groups in the Central India Eye and Medical Study study. This corresponds to the decreased lens thickness noted among Alaskan Eskimos above the age of 65 years. Whether this is related to a cohort effect related to socioeconomic changes in the past is difficult to ascertain. Although both populations were rural in origin, they differ in ethnicity, cultural practices and geographical living conditions. If the first decade of life is critical in determining final refractive error, then environmental and nutritional changes at that time could strongly influence final adult biometric measures. These differences could also be related to measurement bias related to differing ultrasound velocities through dense nuclear cataracts, but similar differences have not been reported by other population-based reports. How would these changes impact angle closure prevalence in developing countries? The mean differences in axial length between persons with angle closure disease and normals range between 0.5 and 0.7 mm. These