Cataract incidence

Worldwide, cataract is the commonest cause of blindness: 20m people are believed blind because of unoperated cataract, of whom women account for about 65 per cent. Globally, the biggest concentrations of cataract blindness (about 13m people) are in India, China and Africa, with an incidence put as 50 per cent higher in rural than in urban areas.

This is due in part to the inaccessibility of modern cataract surgery facilities for the developing world at large, and for its rural populations in particular; an Indian study of 2001 found that 95 per cent of patients with cataract had no chance of reaching a surgical centre. An ophthalmologist-led team that visited Burkina Faso in 2002 carried out 52 cataract extractions, out of a total of 68 operations, over a two-week period. Most, 38, used phacoemulsification; others, extracapsular lens extraction. The same report commented that cataract accounted for over 43 per cent of all blindness in sub-Saharan Africa. Cases of cataract development were cited as severe dehydration in childhood, nutritional deficiencies, lack of anti-UV protection and risk awareness, together with lack of access to surgery; it was estimated that only one in 10 patients in the whole region would have the opportunity of cataract removal.

Other studies indicate that genetic factors may also predispose patients of some races to attract cataract development; a Wilmer Institute (Baltimore, US) study reported that deficiency of the gene glutathione-s-transferase, found in some Asian populations, might double the likelihood of developing cataract. Cataract incidence remains higher even in (for example) Indian populations domiciled in the West, where development risks are relatively low.

Once, not so long ago in historical terms, the outlook for patients in the West with incipient cataract was almost equally gloomy. Today, thanks to technical surgical advances such as lens phacoemulsification and IOL insertion through a microincision, the picture looks very different. Even in the developed world, however, cataract remains a major cause of vision impairment in the (growing) older population, surpassed only by AMD (responsible, according to one demographic survey, for over 40 per cent of 'serious' visual impairment, against just under 36 per cent for cataract, up to 75 years of age; after 75 cataract takes pride of place). Cataract surgery is one of the most common operations carried out in countries such as the UK, where over 270,600 operations were carried out in England alone in 2002-2003: probably about 298,00 in the whole of the UK, applying the usual extrapolation formulae. Of these English operations, about 170,480 were in women: not surprising, perhaps, given that median age at operation was 75. (A medical journalist wrote recently that 'most people develop some opacities' after age 60, and that 'by 75, 70 per cent have visually significant cataracts'.)

In Iceland, the ongoing Reykjavik Eye Study found that of 1,384 people aged 50-80 (mean age 66), 489 showed lens opacities. Visual impairment was greater where combined cortical and posterior subcapsular opacities were present: worst where these were combined also with nuclear opacity. Predictably, opacity of the central 3mm optical zone was associated with the greatest loss in VA. An interesting finding was that 'retrodots', oval or round bi-refringent features in the perinuclear cortex, visible on retroillumination, also showed a 'significant' association with diminished VA. Retrodots are thought to be indicative of exposure to oxidative stress.

Ninety per cent of cataract operations in a country such as the UK are now carried out on a daycare basis: more than 243,000 in England in 2002-2003. Median waiting time was nearly five months. A Government pledge to reduce waiting time to three months has led to various fast-track initiatives, including (according to a 2003 article in EuroTimes, the journal of the European Society of Cataract and Refractive Surgery) 'establishment of diagnostic treatment centres (DTCs), importation of foreign ophthalmologists, exportation of UK patients... and farming out to existing private-practice ophthalmologist'. Results of the drive were reported to have included 20 cataract removals per surgeon per day schedules at one Sunderland centre - 'a virtual production line', achieved by using nurses for history taking, eye examination, biometry, immediate pre-operative assessment and handling post-operative clinics, together with operation list planning. Oxford Eye Hospital was reported to have transferred 25 per cent of its cataract caseload, worth £750,000, to a private DTC, when its waiting list was over 1,300.
At Moorfields, a publicly funded DTC unit reported that its routine was to carry out patient pre-assessment on a Monday, with day surgery seven days later, discharge of most patients taking place one hour postoperatively. One postoperative visit was routinely allocated, three weeks later.

The second eye underwent cataract removal after six weeks if necessary. Using this system 2,365 cataract removals were accomplished over an eight-month period, of which, it was estimated, 80 per cent could be rated 'non-complicated'.

Elsewhere, the practice of simultaneously removing both cataracts is increasingly popular; one Russian team has reported positive results and strong support from patients enlisted for a 1,000-case study of simultaneous bilateral cataract removal.

Clinically, the most serious postoperative complication associated with cataract surgery is endophthalmitis; incidence is low (six cases from a
1,842 case series reported from the US in 2003), but strenuous measures are being taken in a number of countries to reduce it well below 0.1 per cent of all cases.

Most cataract surgery involves the over-70s; neonates may also require removal of congenital cataracts. A study of the Hospital for Sick Children, Toronto, found that best results were achieved when surgery was carried out within the first weeks of life, despite the technical problems involved; if it was deferred to the age of two months, nystagmus and strabismus were more likely to develop. Canada sees about 100 full-term babies born each year with congenital cataract; in 33 per cent this is posterior capsular in nature. Twenty-one per cent of cases had other ocular or systemic problems; 6 per cent had a family history of cataract.