Secondary glaucomas: the tasks ahead.

While the prevalences of morbidity and visual impairment due to primary open angle and angle-closure glaucomas have been fairly well established by population surveys in the west and, recently, in the developing world, the issue of blindness from secondary glaucomas has received little attention from most investigators. Individuals with secondary glaucoma tend to report promptly to the ophthalmologist since there is often marked reduction in visual acuity, apart from pain and ocular discomfort. As a consequence, these are largely self-reported. Information on secondary glaucomas in published eye surveys is limited and the cause of glaucoma seldom identified, although in several prevalence studies secondary glaucomas are numerically important (Table ​(Table1). 1). Based on the WHO Blindness Data Bank, Thylefors and Negrel, in their world estimate of glaucoma blindness, found it was not possible to determine the number of blind from secondary glaucoma, although they estimated the world prevalence to be 2.7 million.1 Quigley emphasised that few studies describe secondary glaucomas as a separate entity and most investigators do not provide the criteria used in defining this potentially blinding disorder. The mean prevalence of this condition is 0.44 [SD 0.36%] or 18% of the mean prevalence of primary open angle glaucoma in the world.2 Quigley estimated that 6 million people in the world have secondary glaucoma compared with 67 million with the primary glaucomas. Table 1 Prevalence of Secondary Glaucomas as Reported by Population Based Surveys The Glaucoma Services at the Aravind Eye Hospital, a large tertiary eye care centre in South India, registered 367 individuals with various secondary glaucomas (Table ​(Table2)2) in the year 2000. This represents about 6.0 % of total new cases of glaucoma seen annually. Table 2 Common Causes of Secondary Glaucomas seen in a Tertiary Eye Care Hospital in South India. ∗ Lens Induced Secondary Glaucomas Lens induced glaucomas due to hypermature cataracts are an important cause of secondary glaucoma in the developing world. Cataract accounts for 50–80% of the world's blind and in the developing world financial, cultural and psychosocial barriers to accessing excellent surgical services still exist. There is an ever increasing backlog of cataract due to the population explosion, increased life expectancy and low productivity in terms of utilisation of the available surgical services. The uptake of eye care services by the rural community has also been suboptimal in countries like India3 where lens induced glaucomas are a common cause of ocular morbidity. It should be recognised that reduced vision is not the only indication for cataract surgery. An enlarged, cataractous lens can cause phacomorphic glaucoma (see below), the treatment of which is removal of the lens. Under Vision 2020, the global initiative of the WHO and voluntary service organisations, to reduce significantly ‘avoidable’ blindness by the year 2020, it is intended that cataract surgeries performed will increase, particularly in the developing nations. Currently, it is estimated that about 12 million cataract operations are performed each year the world over. Vision 2020 aims to achieve a target of about 20 million cataract operations by the year 2010 and ultimately reach a target of 32 million people receiving cataract surgery annually by 2020. Although recent advances in sutureless small incision cataract surgery and phacoemulsification and improved IOL designs have resulted in vastly superior outcomes with reduced complications related to wound repair and secondary glaucomas, several problems still remain. These require training of ophthalmologists in the emerging, new techniques and tackling complications peculiar to the new surgical methods, which may include glaucoma and inflammation secondary to retained lens fragments. These measures will also reduce complications such as pseudophakic glaucoma, for example, yet another significant cause of secondary glaucoma. Phacomorphic glaucoma The cataractous lens may become swollen (intumescent) which causes relative pupil block, the iris root is moved forward and this may result in blockage of outflow of aqueous fluid at the angle of the anterior chamber. This is a secondary form of angle-closure glaucoma.