Cataracts are responsible for the majority of cases of both blindness and visual impairment worldwide. The World Health Organization estimates that 18 million people are bilaterally blind from cataracts. Cataract surgery has been shown to be one of the most cost-effective healthcare interventions, but the availability of cataract surgery varies dramatically when developed and less-developed countries are compared. This is manifested in regional blindness rates due to cataract. The proportion of blindness due to cataract ranges from 5% in Western Europe and North America to 50% in poorer regions. Cataract surgery is one of the most frequently performed operations in developed countries and it is the most frequently performed operation among Medicare participants in the United States.
The relationship between cataract and advancing age is clear. In the Framingham Eye Study, the prevalence of age-related lens changes was 42% in individuals aged 52 to 64 years. This figure increased to 91% for ages 75 to 85 years. Visually significant cataract occurred in 4% of the former group and in 50% of the latter. Subsequent data collected during a reexamination of the survivors of the Framingham Eye Study showed that the 13.6-year incidence of lens opacities among persons free of opacities at baseline was 50% for persons aged 55 to 59 years at baseline, with this number increasing to more than 80% for the group aged 70 to 74 years at baseline. In the National Health and Nutritional Examination Survey (NHANES), detectable lens opacities were found in approximately 60% of subjects aged 65 to 74 years, with significant associated visual impairment in 28%.
Risk Factors for Cataract
When cataract is defined as anything less than total optical clarity of the human crystalline lens, then the majority of adults over the age of 60 will demonstrate some form of cataract. Using this definition, aging becomes synonymous with the development of cataract, so that aging is a major risk factor for cataract. It must be emphasized that these “optical” cataracts may not be clinically significant.
Epidemiologic studies have conclusively shown that chronic exposure to ultraviolet radiation (UVR) is associated with an increased incidence of visually significant cataracts. Effective and consistent ocular UVR protection—preferably begun early in life when the risk to the eyes posed by UVR is highest and exposure levels greatest—through the use of UVR-blocking eyewear can potentially decrease the subsequent incidence of cataract. Additional risk factors for age-related cataract that are potentially addressable through Healthy Sight Counseling include smoking, dietary deficiencies, alcohol consumption, hypertension, diabetes, and medication use. (See Table 1).
| TABLE 1: Risk Factors for Cataract |
|
Factor |
Finding |
|
UVR exposure |
Found to be one of the most important independent factors for the development of cataracts |
|
Hypertension |
Association between elevated blood pressure and cataract has been suggested but not established conclusively as an independent factor |
|
Diabetes |
Adult-onset diabetes: age alone may be an important determinant
Younger persons with diabetes: an important factor is the duration of diabetes |
|
Smoking |
Increased risk of lens opacities associated with smoking (possibly related to impairment of antioxidant defense mechanisms by cigarette smoke) |
|
Alcohol |
Several studies have found an association between alcohol consumption and cataract. However, the mechanism by which alcohol use could result in cataract is not clear |
|
Awareness of risk |
Low level of awareness of the risks is an important factor. This can be countered with adequate patient education |
|
Gender |
Small, increased risk of cataract among women, specific to cortical cataracts |