Cataract is a symptomatic opacification of the crystalline lens of the eye. Opacifications may be present without the patient having any awareness of them. Once symptoms develop, or changes in vision occur, these opacifications are referred to as “cataracts.” If untreated, cataracts may lead to profound vision loss.
The most common type of cataract is referred to as “age-related.” Its etiology is multifactorial. Although genetic factors may predispose an individual to opacifications, limiting the amount of UV light exposure as well as eliminating other risk factors such as obesity, type 2 diabetes, and cigarette smoking, may prevent the opacifications from becoming symptomatic.
“Age-related” cataracts are the most common type, but opacities may also be caused by congenital conditions, trauma, and radiation exposure. The condition is responsible for approximately half of all cases of severe vision loss in the world, affecting an estimated 16 million people. Opacities can be either diffuse or localized, and cataracts are usually classified according to the region of the lens affected: cortical, nuclear, posterior subcapsular, or mixed. Loss of transparency occurs with increasing accumulation of pigment within the lens.
Symptoms are progressive, not painful, and usually bilateral. Specific symptoms may include:
- Difficulty seeing printed text or worsening ability to read
- Excessive glare during night driving and in bright sunlight
- Halo effect around lights
- Deterioration of distance vision more than of near vision, known as “myopic shift,” occurring with nuclear cataracts in individuals over 70
In the US, the prevalence of cataracts is highest in White individuals, followed by non-Hispanic Black and Hispanic individuals.
Type 2 diabetes mellitus. Diabetes increases the risk for all types of cataracts
Corticosteroids. Systemic and inhaled steroids increase the risk of posterior subcapsular cataracts.
Tobacco use. Cigarettes and smokeless tobacco are both dose-related risk factors for cataract development. Up to 20% of cataracts in American men can be attributed to smoking. Quitting may partially reverse the disease in the nuclear and posterior subcapsular forms.
Alcohol use. Alcohol has been shown to be a risk factor in women. See Nutritional Considerations below.
Extensive sunlight exposure; i.e., photo-oxidation secondary to UV-B. Risk is dose-related.
Chronic lead exposure.
Metabolic syndrome. Thought to be due to increased oxidative stress
Physical inactivity. Activity such as walking, bicycling, and a nonsedentary occupation reduces risk of age-related cataract.
Risk of cataract is also increased by the use of phenothiazines, ocular radiation exposure, trauma, uveitis, and malnutrition.
Most cataracts are observed during routine evaluation. During a nondilated examination in a room with dim illumination and the focusing dial of the ophthalmoscope set at “0,” the doctor observes the patient at arm’s length. Opacified areas of the lens may appear as silhouettes within the red reflex, or the red reflex may be darker than normal. Once noted, a comprehensive eye exam should be performed.
Providers should inquire about any changes in vision, recent eye injuries, or changes in medication.
Once diagnosed with cataract, the patient should be referred to an ophthalmologist for further evaluation and possible extraction.
Current treatment for cataract is exclusively surgical. The opacification is removed as soon as the visual impairment begins to interfere with daily activities and an artificial intraocular lens is placed. Adverse events are rare, and the recovery time is short. There is no advantage to removing an asymptomatic opacity.
Epidemiologic studies have shown associations between several nutritional factors and cataract risk. These factors have not been tested in controlled intervention trials, but the principal factors under study are listed below:
Maintaining serum lipids within established norms. Researchers have identified relationships between elevated levels of triglycerides, chylomicrons, and very-low-density lipoprotein and increased cataract risk., There appears to be an inverse association between high-density lipoprotein concentrations and cataract risk.
Maintain blood glucose levels within established norms. Diabetes mellitus increases cataract risk. Diets including larger quantities of high-glycemic-index foods have been found to be associated with increased risk. High-fiber complex carbohydrates from whole grains, beans, and vegetables, conversely, appear to be protective (see Diabetes Mellitus chapter).
Modifying fat intake. Cataract risk could be influenced by the type and amount of dietary fat. Compared with those eating the least fat (25% of calories), those eating the highest amount (37%) had a 10% greater risk for cataract., Women consuming the highest percentage of energy from essential fatty acids (6% of calories from linoleic acid and ~ 0.7% calories from alpha-linolenic acid) had over twice the risk for cataract compared with those consuming the least (4% and ~ 0.5%, respectively).
In the Nurses Health Study involving more than 71,000 women, eating fish > 3 times per week was associated with a 12% lower risk for cataract extraction compared with women eating the least fish. The Blue Mountains Eye Study found a roughly 40% lower cataract risk in individuals who consumed the highest amount of total omega-3 fatty acids, but found no protective effect from fish consumption alone.
Avoiding dairy products. Persons with heterozygous galactokinase deficiency and elderly persons who have diminished activity of this enzyme are at higher risk for cataract., Dairy products, which contribute most of the galactose to the diet, should be avoided in these patients.
Eating more fruits and vegetables. Since antioxidant-rich diets are associated with a lower risk of cataracts, the incorporation of more vegetables and fruits may prevent or slow the condition’s progression.
Consuming more carotenoid-containing vegetables. The consumption of higher intakes of lutein and zeaxanthin, two carotenoids present in dark green, leafy vegetables and corn, has been associated with a reduced risk of cataract in several extensive epidemiological studies. Within the crystalline lens, these carotenoids may protect against cataract by preventing the oxidation of lens proteins.
Emphasizing antioxidant-rich foods. Some evidence suggests that high doses of antioxidants help prevent cataract formation, and that the antioxidant vitamins C and E may retard the progression of cataract., A 10-year study with 300 pairs of twins found an inverse relationship with dietary vitamin C consumption and cataract progression. Good sources of vitamin C include citrus fruits, peppers, tropical fruits, cantaloupe, strawberries, kiwifruits, cruciferous vegetables, tomatoes, potatoes, and sweet potatoes. Good sources of vitamin E include wheat germ, cooked spinach, soy milk, many varieties of nuts, sunflower seeds, mangoes, and olive, peanut, and vegetable oils.
Vegetarian and vegan dietary patterns. Researchers in the UK examined the diets of 27,670 nondiabetic participants in the European Prospective Investigation into Cancer and Nutrition study (EPIC-Oxford) and found a decrease in risk in cataract formation among those who ate the least meat, with vegetarian and vegan diets being the most protective.
Avoidance of alcohol. Compared with nondrinkers, individuals who consumed more than 2 glasses per week of any type of alcohol (beer, wine, or distilled spirits) had a 13% higher risk for nuclear opacity. In the Swedish Mammography Cohort study of nearly 35,000 women, having 1 drink per day was associated with a 7% greater risk for cataract extraction compared with avoiding alcohol.
Protein intake. Several studies have shown that higher protein intakes are associated with reduced cataract risk. In the Blue Mountains Eye Study II involving a 5-year follow-up of more than 2,300 individuals over 49 years of age, an estimated protein intake of 107 grams per day is associated with a roughly 70% lower risk for posterior subcapsular cataract when compared with a protein intake of 71 grams per day. Possible explanations for these findings include an association of high protein intakes with certain nutrients considered to be protective against cataract (e.g., beta-carotene, zinc) and prevention of osmotic stress to the lens through albumin, which is maintained by high protein intake. The potential benefit for cataract prevention, however, must be weighed against the risk of diseases associated with excess intake of protein (e.g., kidney stones; see Nephrolithiasis chapter) and of the fat and cholesterol that often accompanies animal protein.
See Basic Diet Orders chapter.
In cases of galactokinase deficiency, avoid dairy products.
Control of plasma lipid concentrations (see Hypertension chapter).
Limit sun exposure.
What to Tell the Family
It is important for the patient and family to understand that cataract is not a cancer, and that harm rarely occurs to the remainder of the eye structure. The timing of surgery, if decided upon, depends on the patient’s perceived degree of disability. When surgery is necessary, the chance for restoration of vision is excellent. Vision may not be restored entirely, however, if other factors have contributed to vision loss, such as diabetic retinopathy or age-related macular degeneration. Prior to cataract surgery, ophthalmologists perform tests to estimate how much vision may be recovered.
Supplements of lutein or other antioxidants should not take the place of a diet rich in dark, leafy green vegetables. The possible benefit associated with vegetables may be partially due to the presence of other phytochemicals that have not yet been fully identified. Since family members of patients with cataract are also at risk for cataract, their adoption of a similarly healthful diet is advantageous. The family can also help the patient avoid tobacco, alcohol, and excessive sunlight.Tthese diet and lifestyle changes offer many additional health benefits.
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