The Classification of Primary Angle-Closure Glaucoma
The most familiar classification of angle-closure glaucoma is based on the presence of symptoms. This approach fails to recognise the large number of asymptomatic patients and people at risk.
Classification based on symptoms does not guide the ophthalmologist in devising a logical management plan and predicting prognosis.
The term “glaucoma” is currently used indiscriminately, regardless of the presence or absence of optic neuropathy. Its use should be restricted to cases in which there is evidence of glaucomatous optic neuropathy.
The terms anatomically narrow angle and occludable angle are used interchangeably to indicate an anatomical predisposition to pathological angle-closure. These terms have found widespread usage in epidemiological research, and are generally taken to indicate the presence of iridotrabecular contact (ITC)—the defining feature of angle-closure. ITC is now thought to be significant if the posterior (usually pigmented) trabecular meshwork is obstructed by the peripheral iris for half of its circumference or more. However, this is a conservative approach to the assessment of risk, and may underrepresent the “at risk” population and thus be revised in future.
International expert consensus is that the classification of angle closure should describe the conceptual stage in the natural history of angle closure, ranging from iridotrabecular contact (ITC) primary angle closure suspect), to anterior segment signs of disease, specifically raised intraocular pressure (IOP) and/or peripheral anterior synechiae (PAS), which are the defining features of angle closure in an eye with an anatomically narrow angle (this stage is termed primary angle closure). The natural history finally culminates in glaucomatous optic neuropathy (termed primary angle closure glaucoma when it occurs in conjunction with angle closure as previously defined).
This classification indicates the presence or absence of abnormalities requiring treatment, and specifies visually significant end organ damage (glaucomatous optic neuropathy).
In addition to describing the stage of disease, it is important to identify the mechanism causing angle closure. This requires an additional system to be used in parallel.
In addition to glaucomatous optic neuropathy, there are several forms of ocular tissue damage that may result in visual dysfunction as a consequence of angle closure, such as cataract, endothelial cell loss and anterior ischaemic optic neuropathy. These should be separately identified clinical management targeted at these specific processes.
The most widely used classification of mechanism is the four-point system, which identifies obstructions to aqueous outflow at progressively more posterior levels: (a) pupil block; (b) ciliary body-induced; (c) lens-induced; (d) retrolenticular causes.
The art of gonioscopy is indispensable to the diagnosis and management of all forms of glaucoma. The development of new anterior chamber imaging techniques in the clinical assessment of angle, such as ultrasound biomicropscopy and anterior segment OCT, are a useful supplement to clinical examination and gonioscopy, which will further improve understanding of the mechanisms responsible for angle closure.
KeywordsTrabecular Meshwork Angle Closure Anterior Chamber Depth Anterior Segment Optical Coherence Tomography Plateau Iris
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