ANGLE CLOSURE

Angle-closure glaucoma accounts for a relatively low proportion of glaucoma cases occurring in Europe and worldwide, but a high proportion of patients become bilaterally blind from the condition despite the availability of effective treatment, John Thygesen MD told a session of the Glaucoma Day of the XXXI Congress of the ESCRS in Amsterdam.

In 2010 there were an estimated 45 million patients worldwide with primary open-angle glaucoma, 4.5 million of whom were bilaterally blind and 16 million cases of primary angle closure glaucoma, 3.9 million of whom were bilaterally blind (Quigley et al. Br J Ophthalmol 2006; 9 : 262-to 267), said Dr Thygesen, Copenhagen University Hospital Glostrup, Copenhagen, Denmark. “Angle closure glaucoma accounts for approximately 25 per cent of all glaucomatous optic neuropathy worldwide, but for nearly 50 per cent of bilateral glaucoma blindness. Therefore, it’s much more dangerous to have angle closure glaucoma compared to open-angle glaucoma,” he added. He said that a difficulty in determining the prevalence and incidence of angle-closure glaucoma is the different criteria used to define the disease in different parts of the world. In Japan there was a tendency some years ago to class all cases of angle closure suspects as angle closure glaucoma if they had undergone peripheral laser iridotomy, even in the absence of visual field loss or detectable damage to the optic nerve head, Dr Thygesen said.

Even the definition of an occludable angle has been controversial. In 2002, the International Society of Geographical and Epidemiological Ophthalmology (ISGEO) defined angle closure as being cases where 270 degrees or more of the posterior trabecular meshwork is not visible by gonioscopy. In 2003 the ISGEO modified that definition to include eyes where only 180 degrees of the posterior trabecular meshwork is obscured.

Therefore, among 1,233 individuals in the Salisbury Eye study, the rate of angle-closure glaucoma would be 0.65 per cent by the 2002 ISGEO definition, but would be 1.54 per cent by the ISGEO definition (Day et al, Br J Ophthalmol 2012: 96:1162-1167). In the natural history of the disease, 10-40 per cent of eyes with an occludable angle develop angle closure within 10 years. Among eyes with angle closure, 28 per cent develop glaucoma after a further five years. Vision loss can be prevented in most cases if they are detected early enough, Dr Thygesen said.

He added that since the initiation of screening for angleclosure glaucoma in the high-risk Inuit population of Greenland, the proportion of the country’s blind population whose vision loss was due to angle-closure glaucoma went from 64 per cent in 1962, to only nine per cent in 1999.

John Thygesen: thyge-lind@webspeed.dk