Cataract

SURVEY OF OPHTHALMOLOGY VOLUME 45 • SUPPLEMENT 1 • NOVEMBER 2000

CHAPTER 3

Cataract: Epidemiology and Service Delivery The major risk factor for lens opacification is aging. A bewildering array of etiologic factors have been postulated in the causation of age-related cataract (Table 3.1).14,17,36,47,63,70,76,89,98,99,100,115,188,189 Studies have focused on genetic factors,9,19,65,71,92,139,161,179 environmental influences,15,39,42,57,97,103,105,111,118,162,172, 181 and on the metabolic and biochemical changes in the crystalline lens.9,11,13,15,19,20,25,130,161,179 Many investigators believe that an important factor in the pathogenesis of cataract is ultraviolet radiation exposure (Fig. 3.1).21,23,27,37,43,49,102,142,163,164,181,186,192 Brilliant and associates noted a positive correlation between cataract prevalence and sunlight in Nepal.23 A high prevalence of cataract was detected in Northern India in a population living in the plains (4.2– 7.2%), and a lower prevalence (1.5–3.8%) in an adjacent population living at high altitudes in the Himalayas.30 Several reports have noted an increased risk of cataract among cigarette smokers.7,34,38,61,62,64, 68,74,81,90,137,138,143,145,182–185 Minassian and associates121 and Harding and associates67 suggested that severe diarrhea may be a major risk factor for the development of cataract, but other studies have not supported this hypothesis. Several studies have correlated nutritional status and the role of trace elements in cataractogenesis,11,20,60,73,80,130,151,171 and others have implicated alcohol as a factor.38,68,69,124,

the developing world, are given in Fig. 3.2 and Table 3.3. Cataract is the most prevalent cause of visual loss, and this is projected to increase during the next several decades as the median age of the population increases.50,53,56,174,175,178 Normally, when we speak of cataract, we refer to the 25 million people with a visual acuity ⬍3/60 who are bilaterally blind from cataract. However, there are at least 110 million eyes with cataract vision of ⬍6/60, which can be termed severely visually disabled. Although the number of cataract extractions per year has been gradually increasing, the current service delivery throughout the developing world is not yet equal to the incidence (new cases) of severely disabling cataract, with the result that the prevalence (backlog) continues to increase.8,32,45,126, 190 The backlog of patients blind from cataract may double to 50 million worldwide by the year 2020,12, 169,180 unless service delivery increases (Fig. 3.2). Unfortunately, there are little data available on the incidence of cataract blindness in various countries. A useful planning figure in developing countries is one new person with cataract blindness per 1000 population per year. However, the figure for severely visually impaired cataract eyes is 3–4 times this figure (i.e., 3,000–4,000 per million population per year). Data from India and Africa suggest that the current level of service delivery is well below the incidence of new cases of cataract causing visual impairment and, hence, the backlog of cataract blindness and impairment continues to grow.59,85,91,93,95,117,119,123, 128,129,133,136,148,149,174,176,177,190 In India, of the 12 million blind, cataract accounts for up to 81% of blindness, 1,18,31,32,40,41,59,107 but, according to Dandona, this estimate may be too high (Table 3.3).40 Currently, in spite of a vast infusion of funds into this area to attack the cataract problem, only 1.5 million cataract surgeries85,133,148 are performed each year. Although the increased use of extracapsular cataract extrac-

131,140,158

Pre-existing diseases, such as diabetes mellitus25,29, and glaucoma,66 may cause cataract, but in most cases of cataract, there is no known pre-existing disease factor. It is useful, for teaching purposes, to simplify this complex list to the “Seven Ds,” which are listed in Table 3.2.70,99

54,66,101,173

Magnitude The authors’ estimates of the magnitude of cataract globally,2,6,10,55,104,112,113,116,122,134,187 especially in S32 © 2000 by Elsevier Science Inc. All rights reserved.

0039-6257/00/$–see front matter PII S0039-6257(00)00171-5

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EPIDEMIOLOGY AND SERVICE DELIVERY TABLE 3.1

Postulated Causative Factors of Cataract Formation Risk Factors

References

UV-B Radiation Smoking Diarrhea Nutritional deficiencies Trace elements Alcohol Pre-existing diseases Diabetes Glaucoma Demographic factors Low education Rural dwellers Low weight/height

21, 23, 37, 43, 49, 55, 102, 142, 163, 164, 186, 192 7, 34, 38, 61, 62, 64, 68, 74, 81, 90, 137, 138, 143, 145, 182, 184, 187 16, 67, 121 60, 62, 80, 151, 171 11, 17 14, 38, 69, 124, 131, 140 25, 29, 54, 66, 101, 173 66 79 26, 135 57, 101

tion with posterior chamber intraocular lenses (ECCE-PC-IOL) has gained public attention,3,4 it still remains a fact that most cataract operations in rural areas are performed with intracapsular cataract extraction (ICCE) and aphakic spectacles.127,170,196 Simple mathematics shows that the backlog of 8.4 million in India plus 2.2 to 3.8 million new cases each year is not even coming close to being decreased. If the status quo continues, or even if the oft-cited goal of increasing the number of operations to 2 million per year is achieved, the backlog will continue to grow in a rapid uncontrolled fashion.45,46 Similarly, over half of the 6 million blind people in sub-Saharan Africa have surgically curable cataract. The backlog here will also grow, as there is an annual incidence of at least 500,000 new cataractblind patients each year, whereas only 50,000 cataract operations are performed each year.52,190

The Cataract Surgical Rate Although intense research is ongoing, at present there is no effective pharmaceutical treatment of

cataract; therefore, surgical treatment is the only way to treat this blinding condition and the only way to meet the need for cataract service is to increase the number of operations.24,82,84,87,94–96,106,125,141,166,187 One measurement of the quantity (or output) of cataract service is termed the cataract surgery rate (CSR). This is defined as the number of cataract operations/ year/1 million population.91,150,177 The growth of the cataract backlog is schematically illustrated for blindness and operable cataract in Fig. 3.3, and the factors involved in the interaction between incidence, CSR, mortality and backlog are shown diagrammatically in Fig. 3.4. The four main barriers to obtaining cataract surgery are lack of patient awareness, poor quality of service, cost of surgery, and distance to the surgical site. To increase the cataract surgery rate, these factors have to be minimized. Fig. 3.3 left illustrates the scenario of a backlog of 25 million, in which 5 million people become newly blind each year. If only 1 million per year are operated on, and assuming 3 million per year die, then the backlog of people blind from cataract has increased by 1 million. In the group with visual disabilities (⬍6/60) (Fig. 3.3 right), the figures are even more discouraging. Assuming 30 million new cases per year, assuming a backlog of 110 million (Fig. 3.3B), and assuming 10 million operations per year with a mortality of 7–15 million within this population, the backlog increases to 5–13 million individuals per year. Most tragically, the individuals who are listed under “mortality” in each group have died without ever having enjoyed restoration of vision. Table 3.4 and Fig. 3.5 give the estimated CSR for several regions of the world, as classified by the IAPB and the World Health Organization (WHO). A cataract surgery rate of around 4,000–6,000 per million is common in most developed countries, whereas rates as low as 300 per million are seen in some developing countries of Africa and, in some areas of China it is probably less than 200 per million.28,75,114, 153,156,159,160,195,198–202

TABLE 3.2 TABLE 3.3

Cataract Risk Factors—The 7 Ds Major Risk Factors Diabetes Drugs Daylight Dehydrogenase deficiency Minor Risk Factors Dehydration Diet Don’t know

Global Cataract Estimates And Projectionsa Smoking, Alcohol, Steroids, others UVB exposure Glucose 6 Phosphate Dehydrogenase Dehydration, Uremia General deficiency and/ or Micronutrients Unknown factors

Year

Global Population (millions)

1980 1990 2000 2010 2020

4800 5400 6000 7000 8000

a

Estimated number Estimated number of blind people of eyes ⬍3/60 ⬍6/60 (⬍20/400) (⬍20/200)

Sources of data.50,144,167,193

13 16 25 35 50

60 80 110 160 220

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Surv Ophthalmol 45 (Suppl 1) November 2000

Fig. 3.1. Mature and hypermature cataracts are extremely common and often affect much younger individuals in the developing world than in the industrialized world. They are associated with ultraviolet radiation, as well as other environmental and genetic factors. (See also Tables 3.1 and 3.2).

APPLE ET AL

Fig. 3.2. Number of world blind from cataract projected to the year 2020. The red bars represent people with blindness (visual acuity ⬍3/60). In the year 2000, the number of cataract blind is 25 million. By the year 2020, it is projected to be 50 million. The number of people with severe visual impairment (less than 6/60, blue bars) is much higher—approximately 110 million in year 2000—and it is projected to be over 200 million by the year 2020 if no changes in trends occur. (Sources of data.50,58,167,169,193,194)

Fig. 3.3. Diagrams demonstrating why the number of cataract blind and visually impaired continues to grow. The backlog of cataract surgery is impacted by two factors: the number of patients cured with surgery and the number of patients who died during the period. Left: Currently, the backlog of cataract-blind people is 25 million. Under present circumstances, with 5 million new cases, 1 million being treated and 3 million dying, the net increase of cataract-blind people is 1 million/year. Right: There is a backlog of 110 million persons who are visually impaired by cataract, though not blind. Under present circumstances, with 10 million treated and 7–15 million dying without having received treatment, there is an increase of 5–13 million cataract blind. (Sources of data.17,40,50,55,167,169,194,198,200)

EPIDEMIOLOGY AND SERVICE DELIVERY

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Fig. 3.5. Estimates of cataract surgery rates (CSR) in several world regions. Note the wide disparity in cataract surgery delivery, from rates of 200–400 per million in China and Africa to over 5,000 per million in industrialized North America. (Sources of data.17,40,55,167,174,193,194,198)

Fig. 3.4. Cataract situational analysis. If cataract surgery rates (CSR) are greater than the incidence of cataract plus the mortality rate of people with cataract, the backlog of unoperated cataract will decrease. The ABCs of barriers to increasing the CSR are: A (lack of Awareness; B (Bad service); C (Cost); and D (Distance from surgical centers). (Sources of data.50–53)

surgical rates and, hence, the cataract backlog. Developing nations possess on average 1/15 of the wealth possessed by the industrialized nations. Economic factors are the major constraints that inhibit the development of adequate good-quality cataract services.

Table 3.5 shows data on CSR from the various provinces in China, ranging from less than 100 to 1500 per million. Table 3.6 gives 1998 data on the situation in nine countries of Eastern Europe with cataract surgery rates ranging from 740 to 3,440 per million.

Methods of Increasing the Number of Cataract Surgeries Table 3.7 lists many of the obstacles that have been documented as contributing to low cataract

Fig. 3.6. Number of eye doctors per million (year 2000) in various regions of the world. (Sources of data.33,51)

Fig. 3.7. Strategies for finding the cataract blind. The efficacy in finding patients blind with cataract increases as the number increases in this schematic.

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TABLE 3.4

Authors’ Estimated Cataract Statistics Year 1997 a Population (millions)

WHO Region Africa Americas North Rest Eastern Mediterranean Europe Western Russia Rest Southeast Asia India Rest West Pacific Australia & Japan China Rest TOTAL

600 800 300 500 500 900 385 150 365 1500 985 525 1700 155 1275 270 6000

Cataract Operations Mean values (millions) 0.2 2.15 1.65 0.5 0.5 2.1 1.5 0.25 0.35 3.5 3.0 0.5 1.1 0.6 0.25 0.25 9.55

CSR (cataract operations/ million population/yr) 300 2700 5500 1000 1000 2400 4000 1500 1000 2400 3100 1000 670 4000 200 1000 1640

a

Sources of data.17,40,55,167,174,193,194,198

FACILITATING ACCESS TO SURGICAL SERVICES

A large proportion of cataract blind people live in rural areas of developing countries, where both material and financial resources are severely limited22,26, 35,79,88,146–148,154,157 and there are few ophthalmologists. This leaves the rural population with inadequate access to cataract surgery.48,108,109,132 Although the increased use of ECCE-PC-IOL is gaining wide accepTABLE 3.5

Analysis of Provinces in China by Cataract Surgical Rate a Province

Cataract Surgical Rate (operations/mil population/yr)

Hebei Hunan Inner Mongolia Guangdong Hubei Jiangxi Yunnan Shaanxi Sichuan Shanxi Guangxi Shangdong Qinghai Anhui Jiangsu Tianjin Beijing Xizang Guizhou a

Sources of data.114,195,198,200

29 33 116 121 138 158 175 177 180 194 205 207 253 257 290 333 583 1500 Unknown

tance,194,196 many cataract operations in rural areas are still performed without implantation of an IOL. The number of ophthalmologists varies greatly from one region of the world to another. There is about one ophthalmologist per 15,000–50,000 population in the Americas and Europe. In India and China, the number is approximately 1 per 100,000, but in Africa there is an average of only 1 per million population—e.g., 1 per 650,000 in Kenya and 1 per 2.6 million in Ethiopia (Fig. 3.6). The lack of trained manpower in Africa is, therefore, an important reason for low cataract surgical rates, and because of this, some countries have taken the initiative of training medical assistants or ophthalmic nurses to be cataract surgeons.51,133 In Asia, in order to use the available city-based ophthalmologist to provide services for rural populations, eye camps have been used with varying degrees of success.110,117,144,165,197 Ram, in a study of patients having cataract surgery, emphasized that mobile eye camps have been one of the ways to provide low-cost cataract surgery in rural areas.136 Such mobile eye units have proved useful in localities where health delivery services, roads, and communication are poorly developed. Until recently, almost all eye camp surgery has been ICCE with aphakic spectacle correction. There is an ongoing debate on the quality/safety of surgery in eye camps and whether IOLs should or should not be used. The quality of eye camp cataract surgery cannot increase until IOLs and the many benefits of pseudophakia are established in these camps. The “catch 22” is that the ECCE-PC-IOL procedure

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EPIDEMIOLOGY AND SERVICE DELIVERY TABLE 3.6

Analysis of CSR and Ophthalmologists in Eastern European Countries, Late 1990s a Czech Bosnia H Bulgaria Republic Estonia Hungary Latvia Poland Romania Slovakia Population (million) Eye doctors/mil population Eye surgeons/mil population Cataract operations/mil population a

3.8 10 5 740

8.2 — — 1600

10.2 45 14 2450

1.4 25 12 2600

10.0 47 33 3440

2.4 25 25

38.7 30 30

1900

1280

22.5 25 5 1260

5.4 50 20 2420

120,175

Sources of data.

is at present probably not a viable alternative in many of these camps, but this is gradually changing. Various groups72,77,78,155,168,191,193 are looking at better ways of delivering eye services to developing communities. Natchair and associates126 have introduced the concept of a mobile screening unit. This differs from the classic eye camp in that the patients are not operated on in the field, but rather are identified and then offered transportation to a base hospital for surgery. This concept allows for ECCE-PC-IOL surgery to be performed in good working conditions; however, implementation will be costly and requires motivated, well-trained community eye workers. There are different strategies for overcoming the barrier of distance and improving access to cataract surgery, as illustrated in Fig. 3.7. Most important is the identification of cases in the villages by community (eye) workers.

information about patients in relation to the types of procedures and IOLs that should be utilized in the developing world.5,22,26,28,83 The causes of poor outcome after surgery are summarized in Fig. 3.8. Highquality vision is achievable with well-done IOL surgery, which allows the patient to regain vision before he or she becomes completely dependent on others. The expectation of a better visual outcome increases the patient demand for surgery. In a well established eye clinic in Nepal, the number of patients seeking surgery has increased markedly with the use of both AC- and PC-IOLs (Fig. 3.9). As was illustrated in Fig. 3.7, there are multiple strategies for finding the cataract blind; and a combination of these should be used. The appropriate strategy for improving cataract service depends upon whether or not there is a waiting list (Fig. 3.10).

IMPROVING QUALITY OF VISUAL OUTCOME AFTER CATARACT SURGERY

To remove one of the major constraints to providing cataract surgery, it must be made affordable to poor people (Fig. 3.11). The costs of cataract surgery can be simply divided into two main categories: consumables, which are needed for each operation; and overhead, or the cost of maintaining the facility. Consumables include pre- and postoperative care, e.g., medicines, sutures, IOLs, spectacles, etc. The total cost of these items increases with the number of procedures done. To reduce the cost of consumables per case, one should use only essential supplies and use appropriate low-cost technology. Overhead costs are the same whether one procedure or 1,000 procedures are performed, e.g., salaries, buildings, water, electricity, rent, instruments, equipment, etc. For these items the cost per operation decreases as the number of operations increases. Efficient utilization of resources is required. In order to provide cataract surgery at an affordable price (Fig. 3.11), it is first necessary to exercise cost-containment. This may be accomplished by using appropriate low-cost technologies and by maximizing the utilization of personnel and other resources in order to improve efficiency. However, even when the cost of cataract surgery has been low-

It is increasingly recognized that poor visual outcome after cataract surgery is not uncommon in developing countries and is a major reason for lack of patient acceptance of surgery. Several recent studies in a developing world setting have provided valuable TABLE 3.7

Reasons for Cataract Blindness in the Developing World • Lack of trained manpower, particularly in rural areas and generally in Africa. • Lack of instruments, equipment and supplies, combined with poor maintenance and support capabilities. • Other health priorities, e.g., malaria, AIDS. • Poor access to eye care by rural populations. • Fear and misunderstanding of cataract surgery. • Poor surgical results, and problem of spectacle rehabilitation. • Lack of norms and practice guidelines for cataract surgery. • Poor coordination between government and nongovernmental services. • Government bureaucracy.

MAKING CATARACT SURGERY AFFORDABLE

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Fig.3.8. Common causes of poor outcome of cataract surgery.

ered as far as possible, the price may still be too high for poor people. It is then necessary to reduce the price to the consumer through a subsidy. The subsidy can come from a variety of sources, preferably local, (e.g., payment by richer patients can subsidize services for the poorer, or less essential eye services,

Fig. 3.9. Data from the Lahan Eye Hospital, Nepal, staffed by Drs. Albrecht Hennig and D. Pradham, sponsored by Christoffel Blindenmission (CBM), demonstrate that providing good surgical results over the past few years, especially those possible with IOLs, has rapidly increased patients’ awareness of the efficacy of IOLs. Note increased numbers of patients attending the clinic and the surgical operating room. Top: Outpatient visits at the Lahan Eye Hospital. Bottom: Operations (the vast majority cataract procedures) at Lahan Eye Hospital. IOLs have been implanted since approximately 1993.

Fig. 3.10. The appropriate strategy for improving cataract service depends upon whether or not there is a waiting list. If there is none, the demand needs to be increased. If there is a waiting list, utilization of resources needs to be improved.

e.g., selling reading spectacles, can generate income for cataract surgery). If adequate subsidy cannot be obtained from such sources, it may be necessary to seek subsidies from external donors. Provision of subsidies for cataract operations should be seen as a good investment by governmental and nongovernmental sources. As was noted in chapter 2, blindness in general and cataract in particular pose an extreme economic burden on a population. Sha-

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Fig. 3.11. Reducing the cost of cataract surgery in some developing world settings consists of a combination of actually containing the costs of surgery and providing supplemental funds or subsidies from clinical income and other sources. (C ⫽ cost; S ⫽ subsidy).

manna and associates in India reported that the economic loss from work for every million population (with approximately 10,000 blind people including 250 blind children) is $4.5 million per year. To perform 4,000 cataract operations per million per year, sufficient to eliminate blindness from cataract, would cost only a fraction of the above, approximately $200,000 for India.152 As we strive to reduce the cost/price of cataract surgery (Fig. 3.11), it is important that we do not simultaneously reduce the quality of the operation. For example, the incidence of the complication of posterior chamber opacification (PCO) might be expected to increase as a transition from ICCE toward ECCE occurs, especially so-called “simple ECCE” (see chapter 6). This is the reason for needing a great deal of education/treatment of health care providers. Indeed, there have been several recent advances in the prevention of PCO, which are discussed in detail in chapter 7.

IMPROVING UTILIZATION OF AVAILABLE RESOURCES

When CSR is low and there is no waiting list for surgery, there is a need to increase patient demand by addressing the barriers of a lack of awareness, quality and cost of service, and the distance to access

Fig. 3.12. Factors to be considered in evaluating the outcome of surgery.

eye care. If there is a waiting list of patients needing cataract surgery, then resources must be used more efficiently (manpower, theatre [operating room] time, beds, etc.) to reduce and then eliminate the waiting list (Fig. 3.11).

Outcome Although the goal is to increase the CSR, it must be acknowledged that not every eye operated on becomes a significantly improved seeing eye. For example, several studies have shown poor visual results of cataract surgery in many developing countries. This, therefore, makes an analysis of outcomes a critical factor in truly assessing results. It is difficult to measure outcomes in a field situation in the developing world setting. However, such measurement must be attempted if we are to determine the best methods of treatment. Several excellent reports on analyses of outcomes have been published.46,167,193 Fig. 3.12 documents a number of factors that can be measured to evaluate the quality of outcome. The definitions of good, borderline, and poor vision are outlined in Fig. 3.13 for classic developing world situations. This figure provides a typical analysis table utilized by researchers in evaluation of surgical outcomes during field clinical trials. It is important to differentiate functional postoperative acuity without correction and best corrected visual acuity. It is

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9.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Fig. 3.13. Commonly used table to monitor post-cataract surgery results, utilizing 3 levels of Snellen Visual Acuity. (G ⫽ good; B ⫽ border-line; P ⫽ poor). The bar graph below shows a highly desirable outcome scenario. Note in this instance good (G; green) surgical results are gradually increasing, while number of borderline (B; white) and poor (P; red) outcomes is diminishing.

hoped that as the quality of surgery improves in the future that the standards noted in Fig. 3.12 will become higher. The remaining chapters of this monograph will focus primarily on accomplishing the goal of providing pseudophakic visual rehabilitation to all populations of the world.

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