Predisposing factors for chronic angle-closure glaucoma
Introduction
Chronic angle-closure glaucoma is an anatomical disorder of the anterior segment of the eye characterised by permanent closure of part of the filtration angle as a result of iris apposition to the trabecular meshwork. The subsequent rise in intraocular pressure can cause optic nerve damage that is indistinguishable from that found in chronic open-angle glaucoma. It is one of the clinical forms of primary angle-closure glaucoma.
Chronic open-angle glaucoma is the commonest form of glaucoma in North America (Tielsch et al., 1991; Javitt & Sommer, 1991) Europe (Hollows and Graham, 1966) and Africa (Bartholomew, 1976) and acute angle-closure glaucoma is the commonest presenting feature of primary angle-closure glaucoma in Europeans (Leighton et al., 1971). It is therefore not surprising that researchers have concentrated on these forms of glaucoma. However, recent prevalence studies undertaken in East Asia (Congdon et al., 1996; Foster et al., 1996). have shown that chronic angle-closure glaucoma is more prevalent than open-angle glaucoma in Sino–Mongaloid populations, which suggests that chronic angle-closure glaucoma could be the most prevalent form of glaucoma in world-wide terms. It is clearly the most important cause of preventable blindness in elderly East and Southeast Asians (Lim, 1979; Congdon et al., 1992). The demographical and anatomical factors which play a role in the development of chronic angle-closure glaucoma will be considered in this review.
Section snippets
Nomenclature and definitions
The word “glaucoma” does not refer to a single disease entity but rather to a group of diseases that differ in their pathophysiology, clinical presentation and treatment. The most useful classification system was introduced by Barkan (1938) and divides the acquired glaucomas into open-angle forms and angle-closure forms.
When the intraocular pressure is raised in open-angle glaucoma it is because of increased resistance to aqueous outflow through the trabecular meshwork—Schlemm's
Ethnicity as a risk factor
Ethnicity was not recognised as a major risk factor for chronic angle-closure glaucoma by Ida Mann (1966) in her book “Culture, Race, Climate and Eye Disease”. Although it was suspected in the 1980s that chronic angle-closure glaucoma might be more common in Asians than in Europeans, it was only in 1992 that a comprehensive review of the literature (Congdon et al., 1992), confirmed that ethnic background plays a major demographical role in this condition.
This conclusion was based mainly on the
Age
The prevalence of chronic angle-closure glaucoma increases with age and the diagnosis is made in most patients in the seventh decade of life (Salmon, 1993b). In Southeast and East Asia however, patients often present with advanced chronic angle-closure glaucoma at an early age (Loh, 1968; Lim, 1979). The anterior chamber depth decreases with age; a trend that has been clearly demonstrated in prevalence studies on individuals of mixed Southeast Asian ethnic background (Salmon et al., 1993). When
Anatomical risk factors
The measurement of eyes with primary angle-closure glaucoma and the relationship of one intraocular structure to another was comprehensively documented in Europeans more than 25 years ago (Lowe, 1969a, Lowe, 1969b, Lowe, 1970). In comparison, ocular biometry has only recently been reported in individuals of Southeast Asian and Sino–Mongoloid ethnic background with primary angle-closure glaucoma (Salmon et al., 1994; Congdon et al., 1996). These studies have established that eyes with primary
Future directions of research
Prevalence studies need to be undertaken in Southeast Asia, the Indian subcontinent and the Middle East to determine whether the prevalence of chronic angle-closure glaucoma is the same as that found in Mongolia and China. Although it has been shown (Wilensky et al., 1993) that there is no parameter that is sensitive enough to predict which eyes with a shallow anterior chamber and an occludable angle will later develop primary angle-closure glaucoma, the sensitivity and specificity of the
Conclusion
Chronic angle-closure glaucoma is a common cause of blindness in Asia. Many East and Southeast Asians live in Europe and North America and so an understanding of this form of glaucoma is important for ophthalmologists throughout the world. This review has considered the demographical and anatomical risk factors underlying chronic angle-closure glaucoma and has highlighted the need for further research into the disease so that the necessary steps can be taken to prevent visual loss in these
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