Ординатура / Офтальмология / Английские материалы / Handbook of Nutrition and Ophthalmology_Semba_2007

3.3.17. FRUIT AND VEGETABLE INTAKE

In the Women’s Health Study, a higher intake of fruits and vegetables was associated with a 10–15% reduced risk of cataract (72). The higher level of intake of fruits and vegetables was considered greater than the lowest quintile, or >3.4 servings of fruits and vegetables per day. In the Nurses’ Health Study, of 479 participants aged 52 to 73 yr without previously diagnosed cataract, those who had a higher intake of fruit had a decreased risk of developing nuclear opacities (OR 0.58, 95% CI 0.32–1.05) (63).

3.3.18. FAT INTAKE

There is limited information on the relationship between dietary fat intake and cataract. In the Nurses’ Health Study, of 440 women without cataract, cancer, or diabetes, at baseline, intake of total fat and selected fatty acids was calculated based on five foodfrequency questionnaires between 1980 and the time of a study eye examination in 1993– 1995. Linoleic and linolenic acid intakes were associated with nuclear opacity, but not with cortical or posterior subcapsular opacity (73).

3.3.19. DIETARY GLYCEMIC LOAD

Hyperglycemia may theoretically cause cataracts through disruption of the polyol pathway and increased oxidative stress. A recent large study showed that dietary glycemic load, an indicator of the quality and quantity of carbohydrates in the diet, and glycemic index, a measure of the comparison of the relative plasma glucose response to a specific food compared with a standard source, were not related to the risk of cataract extraction (74).

3.3.20. BODY MASS INDEX

Some studies have suggested an association between high body mass index and risk of cataract (30,75–79), while others have found no association (80). When compared to a body mass index (weight/height2 in kg/m2) of <21, women in the Nurses’ Health Study with body mass index of 23 to <25, 25 to <29, and ≥29, had a relative risk for cataract extraction of 1.56 (95% CI 1.11–2.18), 1.46 (95% CI 1.05–2.03), and 1.65 (95% CI 1.17– 2.32), respectively (75). In a prospective study, men with a body mass index of 22 to <25, 25 to <27.8, and ≥27.8 had a relative risk of incident cataract of 1.54 (95% CI 1.04–2.27), 1.46 (95% CI 0.98–2.20), and 2.10 (95% CI 1.35–3.25), respectively (76). Higher body mass index was associated with an increased risk of nuclear cataract, posterior subcapsular cataract, and cataract extraction (76). In a prospective cohort study involving 714 individuals, aged 52–80 yr, followed for approx 13 yr, a higher body mass index at baseline was associated with an increased risk of cortical opacities (78). An increase in body mass index over time was associated with an increased risk of posterior subcapsular opacities, and no relationship was found between body mass index and nuclear lens opacities (78). A case-control study in northern Italy suggested that both current body mass index and a history of clinically relevant obesity were associated with cataract extraction (77). In addition to high body mass index, abdominal adiposity, as assessed by the waist-to- hip ratio, was an independent risk factor for incident cataract in the Physicians’ Health Study (79). In the Blue Mountains Eye Study, obesity, defined as a body mass index ≥30, was associated with an increased risk of cortical cataract (OR 1.6, 95% CI 1.2–2.2) and subcapsular cataract (OR 2.1, 95% CI 1.3–3.5) (81).

The biological mechanism that might explain such an association is not clear, however, potential causal factors that have been associated with obesity include increased serum uric acid concentrations (31,32,64), higher levels of systemic inflammation (82), and glucose intolerance and insulin resistance (83,84). Obesity is associated with elevations in angiotensinogen, transforming growth factor β, tumor necrosis factor α, interleukin 6, C-reactive protein, and other cytokines and inflammatory mediators, thus, the relationship between obesity and cataract is likely to be complex (85). People with high body mass index are at higher risk of endothelial dysfunction, the metabolic syndrome, and other factors that are associated with a low grade proinflammatory state, as discussed in greater detail in Chapters 4 and 10.

3.4. Other Risk Factors for Cataract

Many different epidemiological risk factors have been identified for cataract, and these include race, gender, social and demographic factors, cigarette smoking, infectious and chronic diseases, nutritional status, environmental factors, and drugs, as has been summarized in some reviews (86–88).

3.4.1. AGE

Increasing age is a well known risk factor for cataract (37,45,86,87,89). The overall prevalence of cataract in the Tibet Eye Study and the Beijing Eye Study by age and sex is shown in Fig. 3 (44).

3.4.2. RACE

In the Lens Opacities Case-Control Study, non-whites were at a higher risk of cortical cataract (32). In the 1971–1972 National Health and Nutrition Examination Survey, blacks were at a higher risk of cataract (89). Blacks, when compared with whites, had a higher risk of nuclear or cortical cataract (13). In the Barbados Eye Study, nuclear opacities were most common among whites, whereas cortical opacities were most common among those of African descent (90). In the Salisbury Eye Evaluation project, among blacks, the risk of having cortical opacities was high (OR 4.0, 95% CI 3.3–4.8) and among whites, the risk was higher of having nuclear opacities (OR 2.1, 95% CI 1.7–2.6) and posterior subcapsular opacities (OR 2.5, 95% CI 1.7–2.6) (91).

3.4.3. GENDER

Women appear to be at slightly higher risk of cataract (31,37,89), and the risk may be specifically associated with cortical cataract (13,31,32,92). Data from 1973–1975 in the Framingham Eye Study suggested that among persons aged 52–85, the sex-specific rates of nuclear, cortical, and posterior subcapsular opacities were 27.9%, 17.1%, and 9.7% for women and 22.6%, 10.6%, and 6.4% for men (37). In the Indian subcontinent, a higher prevalence of cataract has been described in young women compared to men (93). In the Beaver Dam Eye Study, the sex-specific prevalence rates for late cataract in the right eye was 18.7% for women and 11.0% for men (36), and age-adjusted rates show that women were at higher risk for incident cataract over a 10-yr period (41). In the Lens Opacities Case-Control Study, women were at higher risk for cortical cataracts only (32). The reasons why women are at higher risk of cataract are not known. In a recent case-control study conducted among women in India, childbearing was associated with an increased

Fig. 3. Prevalence of cataract in the Tibet Eye Study and Beijing Eye Study by age and sex. (Reprinted from ref. 44. Copyright © 1989, American Medical Association. All rights reserved.)

risk of cataract (94). Women with more than three babies had a higher risk of cataract compared to women with one to three babies (OR 2.2, 95% CI 1.3–3.5), and the risk was even higher for women who had 7–11 babies (OR 4.6, 95% CI 2.0–10.6) (94). Multiple pregnancies may put women at higher risk for micronutrient deficiencies, episodes of hyperglycemia, and other factors that could theoretically contribute to the pathogenesis of cataract.

3.4.4. FAMILY HISTORY

In the Italian-American Cataract Study in Parma, Italy, a history of one or more siblings or parent(s) with cataracts was associated with higher risk of cortical, posterior subcapsular, and mixed cataract (31).

3.4.5. CIGARETTE SMOKING

Several studies have shown an association between smoking and increased risk of cataract (32,84,95–100). Smoking generates free radicals and may potentially affect oxidative stress in the lens itself. Cigarette smokers have been shown to have dietary habits that include a lower intake of dietary antioxidants such as vitamin C, vitamin E, and carotenoids. Smokers may have higher general levels of oxidative stress owing to free radicals generated by smoking as well as a lower intake of dietary antioxidants. In the City Eye Study conducted in London, the relative risk for nuclear lens opacity ranged from 1.0 for past light smokers through 2.6 for past heavy smokers to 2.9 for present heavy smokers (96). Cigarette smoking was associated with increased risk of nuclear lens opacities in

a study of 838 watermen of the Chesapeake Bay in Maryland (97). Among women and men in the Beaver Dam Eye Study, 10 pack-years of cigarette smoking was associated with increased risk of nuclear sclerosis (OR 1.09, 95% CI 1.04–1.16 and OR 1.09, 95% CI 1.05–1.14, respectively) and posterior subcapsular cataract (OR 1.06, 95% CI 0.98– 1.14, OR 1.05, 95% CI 1.00–1.11, respectively) (99). Smoking was associated with increased risk of both severe nuclear cataract (OR 1.3, 95% CI 1.1–1.6) and posterior subcapsular cataract (OR 1.5, 95% CI 1.5–8.2) in the Blue Mountains Eye Study (100).

3.4.6. DIABETES MELLITUS

Diabetes mellitus has been associated with an increased risk of cataract among adults less than 65 yr old, with relative risks of 4.02 and 2.97 described in the Framingham Eye Study and the Health and Nutrition Examination Survey, respectively (101). Diabetes was associated with increased risk of cortical cataracts, posterior subcapsular cataracts, and mixed cataracts in the Len Opacities Case-Control Study (32). Aldose reductose may play a role in cataract formation in diabetics (102). In diabetic animals, administration of quercitrin, an inhibitor of aldose reductase, reduced the accumulation of sorbitol in the lens and delayed the development of cataract (103). Diabetes was also associated with an increased risk of cataract in the 1971–1972 National Health and Nutrition Examination Survey (89), especially posterior subcapsular cataract (13).

3.4.7. ULTRAVIOLET LIGHT EXPOSURE

Ultraviolet radiation is divided by wavelength into ultraviolet (UV)-A (400–320 nm), UV-B (320–290 nm), and UV-C (<290 nm). Most UV-C is absorbed by the ozone layer (104). Various epidemiological studies have suggested a link between UV-B exposure and cataract (13,89,92,105). In the Nepal Blindness Survey, the prevalence of cataract was higher among residents from villages that received an average of 12 h of sunlight per day compared to those from villages with 7 h of sunlight per day (OR 3.8, p = 0.001) (104). In a study conducted among watermen of the Chesapeake Bay, cortical lens opacities were associated with high levels of cumulative UV-B exposure, but no association was found between nuclear cataract and UV-B exposure (105). In a case-control study in Maryland, 168 aphakic cases with a history of posterior subcapsular cataract were matched with 168 controls by age, sex, and referral pattern (106). A history of high exposure to UV-B was associated with an increased risk of posterior subcapsular cataract (106). Increasing UV-B light exposure was also associated with cortical lens opacities among community-dwelling adults, aged 65–84 yr, in Salisbury, Maryland (OR 1.10, 95% CI 1.02–1.20) (107). Individuals who had job locations or leisure activities in the sunlight were at a higher risk of cortical cataract in Italy (31).

3.4.8. DEHYDRATION/DIARRHEA

Severe diarrheal disease and dehydration have been implicated in the pathogenesis of cataract through possible osmotic, metabolic, and nutritional stresses on the lens. Three case-control studies have identified severe dehydrating diarrhea as a risk factor for cataract in India (108–110). In two studies in India, about 40% of cataract in the population was considered to be attributable to severe dehydration or life-threatening diarrheal disease (108,109). Dehydrational crises from severe diarrhea were identified as a major risk factor for cataract in a recent case-control study from Nagpur, India (110). Severe diarrhea was also identified as a risk factor for cataract in Oxfordshire, England (111). In contrast,

no association was found between risk of cataract and lifetime history of severe diarrhea, including cholera, in a case-control study conducted in Tamil Nadu state in India (112). No association was found between a diarrheal disease (an episode confining the individual to bed for 1 d) and cataract (30). Another study from Bangladesh did not find an association between severe diarrhea and risk of cataract (113).

3.4.9. ALCOHOL CONSUMPTION

Alcohol consumption has been associated with an increased risk of cataract (84,95). A two-fold higher risk of cataract was found among individuals who had four or more drinks per day (95). In a case-control study, heavy alcohol use (>91 grams of alcohol per week) was associated with a higher risk of posterior subcapsular cataract (OR 2.70, 95% CI 1.04–6.98) when compared with no alcohol use (114). In the Beaver Dam Eye Study, a history of heavy drinking (four or more drinks per day) was associated with a higher risk of nuclear (OR 1.34, 95% CI 1.12–1.59), cortical (OR 1.36, 95% CI 1.04–1.77), and posterior subcapsular cataract (OR 1.57, 95% CI 1.10–2.25) (115). Current wine consumption was associated with a decreased risk of nuclear cataract (OR 0.84, 95% CI 0.74–0.94). Current alcohol intake was also associated with an increased risk of incident nuclear cataract in the Beaver Dam Eye Study (OR 1.01, 95% CI 1.0–1.02 per 100 g ethanol per week) (40). In the Blue Mountains Eye Study, those who had at least one drink per day had a reduced risk of cortical cataract compared to nondrinkers (OR 0.7, 95% CI 0.6–0.9) (100). Heavy alcohol consumption (four or more drinks per day) was associated with nuclear cataract in current smokers (OR 3.9, 95% CI 0.9–16.6) (100). A “u” shapedrelationship between alcohol consumption and cataract has been suggested, with total abstinence from alcohol and heavy consumption of alcohol being associated with a higher risk of cataract (Fig. 4) (116).

3.4.10. DRUGS

The use of systemic corticosteroids has been associated with an increased risk of posterior subcapsular cataract (32,117). The use of inhaled corticosteroids has been associated with an increased risk of both nuclear and posterior subcapsular cataracts (118) and with an increased risk of undergoing cataract extraction (119). In the Nurses’ Health Study, there was no evidence to support the idea that aspirin use was associated with a decreased risk of cataract (75). Other drugs reported to be associated with cataract include allopurinol and phenothiazines, but the epidemiological data are incomplete (87).

3.4.11. LEAD EXPOSURE

Lead exposure is associated with cognitive dysfunction, hypertension, and increased oxidative stress in older adults. Lead exposure has recently been linked with age-related cataract in older men in the Normative Aging Study (120). Among 663 men, aged 60 yr and older, tibial lead concentrations were associated with an increased risk of cataract.

3.4.12. OTHER FACTORS

A low level of education has been associated with cataract in many different studies (30,31,45,89,106). Low level of education was associated with nuclear, posterior subcapsular, and mixed cataract in India (30). The association between low level of education and cataract appears to be an independent association, as other confounding factors such as dietary intake or sunlight exposure do not explain the association (87). Low

Fig. 4. Relative risk for cataract expressed as odds ratio plotted against six categories of ethanol consumption. (Reprinted from ref. 116, with permission of S. Karger AG, Basel.)

handgrip strength has been associated with higher risk of cataracts (31). The reason for the association between low handgrip strength, an indicator for sarcopenia, and cataract is not clear, but recently, it has been shown that low handgrip, knee, and hip strength in older women is associated with low plasma carotenoid concentrations (121). A recent study from France suggests that low plasma albumin and transthyretin concentrations were associated with an increased risk of cataract (122).

3.5. Cataract and Mortality

Several studies have suggested that lens opacities or a history of cataract surgery is associated with an increased risk of death (123–130), but not all studies have confirmed this association (131). In Boston, survival was compared between 167 patients undergoing cataract surgery and 824 patients undergoing other surgical procedures (123). In cataract patients, the ageand sex-adjusted mortality ratio was 1.78 (95% CI 1.23–2.58), and the increased mortality was not strongly related to diabetes mellitus (123). An analysis

from the Framingham Heart Study suggested that overall, lens opacities were associated with significantly higher mortality, but that ageand sex-adjusted mortality was stronger among individuals with diabetes (death rate ratio 2.62, 95% CI 1.46–4.71) than those without diabetes (death rate ratio 1.17, 95% CI 0.88–1.57) (124). In a study of 473 older, nondiabetic adults in a small English town, those with nuclear cataract at baseline examination had an increased risk of death (adjusted relative hazard for mortality 1.52, 95% CI 1.15–1.99) (125).

Cataract surgery was associated with increased standardised mortality ratio in a study from Sweden, but only in young patients and in patients who had complicating diseases such as diabetes and cardiovascular disease (126). In patients 75 yr of age and older, the standardized mortality ratio was 0.91 ( p = 0.06), whereas in those 45–74 yr of age, the standardized mortality ratio was 1.33 (p = 0.05). In the Blue Mountains Eye Study, of 3654 subjects aged 49 yr and older who were followed from a baseline period of 1992– 1994 until 1999, 16.5% of the subjects died. After adjusting for factors associated with mortality, individuals who had any visual impairment at baseline had an increased mortality risk (relative risk [RR] 1.7, 95% CI 1.2–2.3) (127). The presence of nuclear cataract (RR 1.4, 95% CI 1.1–1.8), cortical cataract (RR 1.3, 95% CI 1.0–1.5), and posterior subcapsular cataract (RR 1.4, 95% CI 1.1–1.8) were also associated with an increased risk of death. In Parma, Italy, a study of 1429 individuals showed that mixed type of cataracts with nuclear and posterior subcapsular cataract was significantly associated with an increased risk of death (128). The biological mechanisms that might explain the association between cataract and mortality include systemic processes relating to aging or increased oxidative stress and inflammation (127,130).

4. CLINCAL FEATURES

For clinical features of nuclear cataract, see Fig. 5; for clinical features of cortical cataract, see Fig. 6; and for clinical features of posterior subcapsular cataract, see Fig. 7.

5. PATHOGENESIS OF CATARACT

The pathogenesis of nuclear cataract, cortical cataract, and posterior subcapsular cataract may differ as related to such factors as the anatomic location and the age of the lens fibers. The nucleus consists of lens fibers that were formed during embryonic and fetal life, whereas the cortex consists of lens fibers that were formed later in life. Lens fibers at the surface of the lens are formed recently, within weeks to months. The lens is located in a low oxygen environment due to the lack of a blood supply, and the lens epithelium and fibers primarily derive energy from glycolysis, using glucose from the aqueous humor (132). Nutrients in the aqueous humor need to diffuse the longest distance to reach the lens fibers of the nucleus. In general, the lens is subject to oxidative stress from molecular oxygen and free radicals generated by mitochondria. Superoxide radicals, peroxide, hydroxyl radicals, and single oxygen are major reactive oxygen species that may be produced in the lens (133). Glutathione is the main antioxidant which protects the lens from oxidative damage (133,134). A common feature of many types of cataracts is a reduction in lens glutathione (134). Glutathione has been hypothesized to protect against cataract formation by preventing the formation of high molecular weight protein aggregates responsible for light scattering and lens opacification, by preserving mem-