There are several types of glaucoma but broadly they can be divided in to 4 groups.
The first division is in to primary and secondary, i.e. depending if the glaucoma is independent of any other concurrent eye disease (primary) or consequent to concurrent eye disease (secondary). Some examples in the latter group include glaucoma secondary to trauma, glaucoma secondary to diabetes induced neovascularisation of the anterior segment and glaucoma secondary to uveitis.
The second division is in reference to the drainage angle which is located in the anterior segment of the eye. Specifically, it refers to the area responsible for egress of fluid from the eye’s anterior chamber – if this area is not working properly, the outflow of fluid will be restricted and the eye pressure, or intraocular pressure (IOP), will increase. If the drainage angle is blocked by the peripheral iris, the angle is referred to as ‘closed’. If the angle is not obstructed but dysfunctional, it is referred to as ‘open’.
Based on these classifications, glaucoma can be divided into 4 basic groups: primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG), secondary open-angle glaucoma and secondary angle closure glaucoma. By far, POAG and PACG are the most common types, with POAG more prevalent than PACG.
PACG is a particular problem in East Asia (including Singapore) as this type of glaucoma is more common in people of East Asian origin than in Caucasians, Africans or South Asians. One condition which can lead to PACG is Acute Angle-Closure (ACC). This condition, one of the few true ophthalmic emergencies, presents with the onset (usually over a period of a few hours) of severe pain, blurred vision and red eye. These symptoms are due to very high IOP which needs to be lowered quickly to reduce the symptoms and decrease the risk of permanent damage to the eye. PACG also results in more blindness proportionally than POAG, which is why glaucoma blindness in Asia is a particular problem