The commonest cause of blindness, according to WHO in 1995,² was unoperated cataract (Fig. 1), somewhere between 40% and 80% in most studies. The global estimates for 1998, taking into account population increases and aging and 1995 service levels, are in excess of 22 million people who are bilaterally blind from cataracts.¹ WHO's definition of blindness (less than 10/200) is based on a social definition of blindness such that an individual cannot move around independently. Other organizations use less than 20/200 as a definition for blindness, a term also known as economic blindness. If the latter definition is used, then estimates of cataract blindness would more than double.

An example of the magnitude of the problem was presented by the World Bank in 1993. Thirteen million people in India were bilaterally blind from cataract, and 10 million were unilaterally blind.² Forty-five percent of cataract patients were younger than 60 years of age. The World Bank estimates that the number of people older than 65 years of age will increase from 37 million in 1990 to 102 million in 2025.

The incidence (number of new cases) of cataract blindness is not accurately known. A WHO consultation suggests a working approximation of one new case of cataract blindness per thousand population per year,³ but this probably is a conservative estimate, and the possible incidence may be as high as 2 per 1000 per year.⁴

In India, the age-adjusted prevalence of cataract is three times that of the United States.⁵ Lepkowski and associates report a significant proportion (55%) of Indians in the 50- to 59-year age group had some form of cataract in either eye.⁶ The World Bank reports that in three states surveyed in India, 24% of cataract-blind persons were in the 50- to 60-year cohort, and 16% were in the 30- to 50-year group. India had at that time an average life expectancy of 60 years, and 40% of those receiving surgery were in their productive years. The average loss of income reported was between 35% and 60% of earning potential. In addition, totally blind people were thought to experience two to five additional injuries in their life compared with a sighted person, requiring an average of 3 days in hospital. Brilliant and colleagues⁷ report that in some areas of Nepal, the 5-year survival rate for blind people was 50% less than nonblind people. In India, Minassian and coworkers⁸ report a mortality rate double that of the normal population.

Disability Adjusted Life Years (DALY) is a measure of health status and is used by health economists to compare the value of different health interventions. It is an indicator of the time lived with a disability together with the time lost as a result of premature mortality. The World Bank in 1993 estimated that between $15 and $32 per cataract removal could save one DALY, making it one of the most cost-effective surgical interventions. A detailed study in the Lumbini zone in south central Nepal over the period 1991 to 1993 concludes that the cost per DALY was much lower at $5.06. Sensitivity analysis for a worst case scenario increased the cost per DALY to $20.53.⁹ A 10% decrease in mortality rate produces a 10% reduction in the cost per DALY, suggesting that as countries improve their life expectancy, the cost effectiveness for cataract surgery programs improves.

WHO estimates that globally in 1995, over 7 million cataract surgeries were performed with a rate of 1100 cataract operations per million people per year. In Europe, the rate of cataract operations in the established market economies was 3000 to 4400; India, 2000; the former socialist economies of Europe, 1000 to 1500; Latin America and the Caribbean, 500 to 1500; the remainder of Asia and the middle eastern crescent, 600 to 1000; sub-Saharan Africa, fewer than 500; and China, about 200 operations per million per year.

To eliminate the backlog of cataracts by the year 2020, over 12 million cataracts need be removed by the year 2000, 20 million per year by 2010, and 32 million per year by 2020. These latter estimates are for treating people who are bilaterally blind from cataract with vision less than 10/200. Ellwein and Kupfer¹⁰ note that up to one third of cataract operations may be for unilateral cataracts. If this is true, global estimates of people relieved from blindness from cataracts may be grossly overestimated. In developed countries and probably in economically richer areas of the developing countries, many cataracts will be removed at an earlier stage instead of when vision is less than 10/200.

A few studies suggest that age-related cataract may be hereditary. The Beaver Dam Study in the United States found that about half of cortical cataract could be explained by the presence of a dominant gene and about one third of nuclear cataract by a recessive gene.^13,14 A study in Australia found an increased risk of both nuclear and cortical cataracts in those with a positive family history.¹⁵ Racial factors also may play a role in people living in the same area. Cortical cataract was four times more common in African Americans than in Caucasians, but nuclear and posterior subcapsular cataracts were only half as common.¹⁶

The association between ocular exposure to UVB radiation (daylight) and cortical cataract seems to be well established and has been confirmed by several epidemiologic studies and by experimental data.^15–17 The effect of diet and vitamins is still unclear. On theoretical grounds, antioxidant vitamins could protect the lens from oxidation and reduce the risk of cataract,^18–22 such as β-carotinoids (vitamin A), ascorbic acid (vitamin C), and α-tocopherol (vitamin E). Although some studies have found a protective effect for one vitamin or another, other studies contradict these findings. It is difficult to assess a lifetime intake of dietary or supplemental vitamins.

Diseases such as diarrhea leading to severe dehydration is, in some studies,^23–25 associated with an increase in cataract formation. Diabetes mellitus is consistently associated with an increased risk of cortical and posterior subcapsular cataract.^26,27 Therapeutic drugs associated with cataract include steroids; whether taken orally, topically, or by inhalation, steroids are associated with posterior subcapsular cataracts.^28–30 Recreational smoking and high alcohol intake also are implicated in causing cataract.^31–33

Other odd risk factors have been suggested by some studies, such as less education, lower socioeconomic status, or rural residence. It seems unlikely that these specific factors themselves would directly cause cataract. It seems more likely that they indicate exposure to, or protection from, some linked factor that the particular study had not identified or measured.

Many people in developing nations lead a subsistence, agrarian life, growing food for themselves and for their extended families and selling the surplus for cash. Characteristics of developing nations are high birth and infant mortality rates and high rates of curable and preventable blindness. Health services are concentrated in the larger cities, and people living in rural areas often live beyond the logistical services of health care delivery teams. Ophthalmologists working in most developing nations are largely concentrated in urban areas.

Most developing nations provide health delivery services through a tiered system, with central hospitals supporting smaller and rural hospitals and health delivery centers. In Africa and Asia, for example, many countries have established a three-tiered system, consisting of primary, secondary, and tertiary levels. The primary health care worker can diagnose and treat the most prevalent disease and refer complicated cases to treatment facilities and promote proper sanitation and good hygiene within the community.

The usual referral resource for the primary health care worker is the secondary facility. Provincial, district, and subdistrict hospitals and health centers serve as secondary medical units.

Ophthalmic assistants, trained in diagnosis and treatment of eye disease and trachoma entropion surgery, staff these secondary static units. Ophthalmologists are assigned to provincial and sometimes to district hospitals.

Ocular surgical services may be provided by mobile eye units based at the central or provincial hospital level. These units visit villages and rural health centres. They are staffed by ophthalmic assistants or ophthalmic nurses and are supervised by ophthalmologists.

The provincial hospital serves as the ultimate referral health facility for all health units within provincial boundaries where general medical and basic specialty services are available.

The central national hospital, usually attached to a medical school, is the tertiary resource. There may be several tertiary hospitals in larger countries serving large geographic regions. This facility usually is a large general hospital and offers a wide range of specialty services. Although it consumes a high proportion of the nation's health budget, it often is overwhelmed by the demand for services. The national (tertiary) eye center provides more sophisticated eye care than that available at the provincial hospital, and ophthalmic subspecialists, if available, are likely to be assigned there. Physicians, medical ophthalmic assistants, and nurses usually are trained at the tertiary hospital. Research relevant to ocular problems specific to the region often is carried out or coordinated from the tertiary hospital.

The ophthalmic assistant is an invaluable resource in any nation where there is a shortage of ophthalmologists. This health worker can examine, diagnose, and manage most patients in need of eye care. Ophthalmic assistants also maximize the efficiency of the limited eye care system by screening and referring only patients requiring surgery or other specialized attention.

Training of ophthalmic assistants is prolonged and intensive. In eastern and southern African countries, for example, qualified applicants receive an initial 3 years of training in general medicine.

On completion of this training, they are posted to a rural health facility to work in general medicine. The aspiring ophthalmic assistants then return for 1 to 2 additional years of ophthalmic training, usually at the national eye center, where they work closely with other medical assistants, ophthalmic nurses, and ophthalmologists.

In some countries, the more technically skilled ophthalmic assistants are taught cataract surgery. Small countries, for example, Tuvalu, an island nation in the Southwest Pacific, population 10,000, may rely on external itinerant services to provide specialist ophthalmic care such as cataract surgery.

PUBLICITY

Publicity may be accomplished through a variety of mechanisms at several levels using health care personnel, radio, television, and other mass media. Blindness organizations and service clubs often are involved in promotional activities.

SCREENING FOR CATARACT

The limited number of qualified ophthalmologists available may mean that ophthalmic assistants often perform the bulk of ophthalmic surgical screening. The primary health care worker also may be taught to identify cataract (Figs. 2 and 3).

MOTIVATION TO OVERCOME PATIENT RELUCTANCE TO UNDERGO SURGERY

Many patients living traditional lives in rural areas, subject to fear and influenced by fatalism, are reluctant to submit to cataract surgery,³⁴ but cultural tradition can be a strong influence in overcoming this reluctance. A significant influence in persuading an individual to undergo cataract surgery is likely to be the example of an individual who has had sight restored by such an operation.^35–37 Result of the surgery, rather than hospital conditions, was the major influence in patients' satisfaction in one study in rural Kenya.³⁸

SURGICAL INTERVENTION

The two commonest surgical methods for removing cataracts in developing countries are intracapsular cataract extraction (ICCE) and extracapsular cataract extraction (ECCE) (Figs. 4 to 6). Aphakic spectacles are needed after surgery unless an intraocular lens (IOL) has been implanted or contact lenses are prescribed. IOLs can be used after ICCE but are not as widely used as with ECCE.

Aphakic spectacles have a limited life, and in some studies,^7,39–41 up to half of the people operated on became blind again because of the loss of or damage to their glasses. Aphakic vision is magnified and has a narrow field of view with “jack in the box” effects. IOL vision simulates “normal” vision if the appropriate IOL is implanted. ICCE still is the most common method of cataract extraction in many developing nations, but ECCE/IOL is now relatively common.^42–44 There are no comprehensive data on the percentage of cataract surgeries associated with IOL implantation.

There are fewer serious long-term complications and better visual function and quality of life with ECCE/IOL surgery compared with ICCE and aphakic correction,^45,46 but little difference in surgical outcomes between ICCE and ICCE/IOL surgery.^47,48 In Africa, however, a preliminary study of anterior chamber implantation among black patients reports an unacceptably high level of persisting uveitis and other complications.⁴⁹ ICCE commonly is performed without magnification, but there appears to be significantly better surgical outcomes with magnification.⁵⁰ The time taken for IOL surgery is unlikely to be a rate-limiting step in the wider context of a cataract program even though the surgical time increases threefold.^47,51

In retraining ICCE surgeons to perform ECCE/IOL surgery, different methods have been suggested, which include intensive short courses and in situ training; however, nonophthalmologists, including nonmedical personnel, also have been successfully trained in either ICCE or ECCE/IOL cataract surgery^50,52,53 (Fig. 7). Standard-power IOLs often are used in mass programs. Several studies of IOL powers among differing populations^54,55 suggest that the use of a single IOL power allows 80% of the population to be within 2.5 diopters (D) and 95% within 5.5 D of the power of the IOL required for emmetropia. One study⁵⁵ found a difference of 1.0 D between male and female patients and recommends a tendency toward higher power IOLs to account for this difference when standard-power IOLs were being used. The added advantage of higher power IOLs was clearer near vision associated with the induced myopia.

In mass cataract programs, the initial aim is to restore functional vision. If most people are within 5.5 D of the IOL power required for emmetropia, this translates at worst to approximately 2.5 D of spectacle power. This uncorrected vision is superior to uncorrected aphakia and allows people to carry out daily living tasks without glasses. The loss of aphakic spectacles effectively renders the person blind again.

The development of posterior capsular opacification is the major drawback of ECCE surgery. The functional visual loss is less than might be expected, however,^56,57 but varies between 5% and 20% at 2 years. Several options exist to deal with posterior capsular opacification. Treatment can be primary or secondary and may involve surgery or the use of neodymium: yttrium-aluminum-garnet (Nd:YAG) laser. Laser has been thought to be a prohibitive option for developing countries, but in a cost-minimization model,⁵⁸ secondary laser capsulotomy, in centers performing more than 1000 cases per year, was a cheaper option than primary surgical capsulotomy when high-cost lasers were used. The recent introduction of low-cost portable YAG lasers will greatly facilitate access to nonsurgical treatment, substantially reducing the number of cases when Nd:YAG laser treatment becomes a cheaper option than primary surgical capsulotomy.

Local and international nongovernment organizations are a major contributor to cataract programs, including direct subsidy, provision of consumables, and capital equipment. Recently, some nongovernment organizations have established locally based factories to provide high-quality, low-cost IOLs where profits are used to expand cataract programs. Indirectly, they assist in skill-transfer activities, train surgeons and allied health personnel, and conduct many blindness prevention activities in conjunction with local authorities.

Patient contributions also are a major source of funds, but this depends on local circumstances. In one institution in India in 1992, 10% of poor people elected to pay for an IOL, and within 2 years this had risen to over 60%.⁶³ Flexible fee-for-service options allow cross-subsidy from richer to poorer patients. Detailed analysis of costs has assisted some institutions to greatly increase their surgical output.⁶⁴

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