Eye Disease, Aging & Human Visual Function
Demographic studies consistently show that age is the best predictor of visual impairment and blindness (Hatfield, 1973, NEI 2004). Aging contributes to visual impairment through both normal deterioration of eye tissues and increased incidence of eye pathology.
According to the National Eye Institute, statistics from a study by their Eye Disease Prevalence Research Group show age-related macular degeneration (AMD), glaucoma, cataract, and diabetic retinopathy are the most common eye diseases in Americans age 40 and over. It is estimated that in 2004, AMD with associated vision loss affected 1.8 million, glaucoma 2.2 million, diabetic retinopathy 4.1 million, and cataract 20.5 million. All of these diseases are expected to increase substantially by 2020 as the population ages. At that time it is projected that nearly 3 million persons will have AMD with associated vision loss. While the numbers for the other eye diseases are higher, AMD is the leading cause of blindness among white Americans; cataract and glaucoma are the leading causes of blindness for African Americans; and glaucoma, the leading cause of blindness worldwide, is the most common cause of vision loss for Hispanic Americans. For those over age 65, AMD is the leading cause of blindness and visual disability. (NEI 2004) The American Foundation for the Blind has estimated that there are now 10 million blind and visually impaired persons with 5.5 million being over the age of 65. However, only 1.3 million are legally blind. (Legal blindness is defined as 20/200 visual acuity or less and/or less than a 20° visual field.) Thus the largest proportion of visually impaired may be described as having low vision and many may be helped with the increasingly sophisticated assistive devices that are now being produced. It is speculated that in the future, because of continued advances in medical and surgical technology and treatment, sight loss will less often be total, and that the relative proportion of partial loss will be greater.
Sight impairment can greatly interfere with the performance of individuals of any age. As described above, sight impairment is loss of acuity and/or restriction of visual field and may be analyzed by measuring acuity and field characteristics. However, these measurements alone do not indicate the severity of interference with daily life. Visual impairment must be characterized by the degree to which one’s behavior is affected. In other words, visual impairment can be defined as interference with the processing of information received through the sense of sight that in turn impedes performance and function.
The effects of a vision impairment on life style can be quite profound. Since vision is the dominant mode of processing information about the environment and one’s ability to move in space, impairment can cause a variety of problems such as inaccurate visual-motor coordination, reduced depth judgment, wide stance and gait, head tilt and/or turn, moving the head close to working material, and unusual viewing positions. Ultimately vision problems can result in a loss of independence.
The frustration of having a visual impairment may lead to depression irritability, disorientation, dizziness, lack of continuity of thought, memory loss, etc. Patients and families must realize that these behaviors are symptoms and that the cause lies in the inability to adapt to the changes in vision. It must also be realized that similar types of impaired sight may interfere with one’s activities to varying degrees, depending upon that person’s needs, habitual activities, support system, and ability to make use of residual vision. Thus the relationship between vision and an individual’s overall situation is complex.
Most of us don’t think much about vision problems until we or our family members begin to develop them. Unfortunately, many serious eye problems (e.g., glaucoma) have no symptoms until vision loss occurs. However, regular eye examinations can result in the early detection of many eye disorders and the preservation of vision in most eye problems benefits from that early detection and management. It is recommended that people over the age of 40 have an eye examination every two to four years, and that those over 65 have an eye examination every one to two years.
The current epidemic of obesity in the United States is associated with a dramatic increase in the prevalence and earlier onset of type II diabetes. Unfortunately, it portends a similar increase in diabetic eye problems. In January 2011, the American Diabetic Association reported that 25.8 million persons or 8.3% of the population of the US now have diabetes. Another 79 million are prediabetic. For those over age 65, the percentage of diabetes increases to 26.9%. Diabetic retinopathy causes 12,000-14,000 new cases of blindness each year making it the leading cause of blindness in adults ages 20-74.
Many visually impaired individuals in nursing homes can benefit from low-vision services with some being rehabilitated and others having an improved quality of life. Various studies show that nursing home residents are between three and fifteen times more likely to have vision problems than those living in the community. Correction of basic refractive errors in one study of nursing home patients (Owsley 2007) showed significant “quality of life and psychological benefits.”
While aging is inevitable, maintaining a healthy life style along with regular eye examinations to detect problems early can help us to maintain better vision throughout our lifetimes.
