[Visual
impairment]
Macular degeneration
Cataract
Glaucoma
Diabetic retinopathy
Visual Impairment
The most important diseases causing visual impairment in older people include cataract, age-related maculopathy (macular degeneration), glaucoma, diabetic retinopathy and retinal vein occlusion. Under- or uncorrected refraction is also a frequent and important component of visual impairment and also contributes to its impacts and disability.
Visual impairment may be present
in one eye (unilateral) or both eyes (bilateral) and its severity can
be considered as mild, moderate or severe. The severity of visual impairment
is measured from the best acuity achieved when reading letters in the
distance on a Snellen or LogMAR vision chart.
Normal Vision
Normal or good vision is considered to be 6/6: This refers to the ability
to read at 6 metres the line a person with good vision can read at that
distance. The term 20/20 actually represents the same level but is measured
in feet, for the United States.
In the Blue Mountains Eye Study (BMES), a decreasing proportion of people could read 6/6 (or 20/20) with increasing age. More than 90% of people aged under 55 years could read this level. However, for people who were aged 85 or older, less than 10% could achieve 6/6 vision after refraction. Women were less likely at all ages to be able to read the 6/6 line and read an average two letters less at each age than men.
Although almost all people seen in the BMES had been prescribed a pair of glasses (either as reading glasses, distance, bifocal or multifocal glasses), many needed a new or different refraction to achieve good distance vision or did not routinely wear their glasses. The project found that almost half of all participants had an improvement of at least one line on the vision chart with a new distance refraction, while one in eight improved by three or more lines. This provides an indication of the magnitude of visual impairment due to under- or uncorrected refraction. Mostly, it was caused by the development of a hyperopic (plus lenses) shift in refraction with increasing age. In some, the onset of cataract caused a myopic (negative lenses) shift in refraction.
Most people from their mid-forties need to use reading glasses, due to loss of accommodative ability with age. Although this trend is inevitable, it is reasonable to delay to some extent the use of reading glasses as the eyes become dependent once readers are used routinely.
Impaired Vision
In the BMES, visual impairment was defined from the better eye as mild
(6/12 to 6/18 vision), moderate (6/24 to 6/60) or severe (legal blindness;
worse than 6/60). A higher
proportion of mild, moderate and severe visual impairment was found in
women than men at each age.
Macular degeneration (age-related maculopathy) was the overwhelming cause of blindness (less than 6/60 vision in both eyes) in the BMES and of moderate visual impairment, while cataract was the leading cause of mild impairment. For visual impairment affecting one eye only, cataract was again the most frequent cause of mild impairment, while cataract and age-related maculopathy were jointly the most frequent causes with moderate unilateral impairment.
Amblyopia (poor vision from childhood, found in 3% of the population) was another important cause of mild unilateral visual impairment.
Impacts of Visual
Impairment
The BMES has reported a number of important impacts of visual impairment
that combine to reduce the independence of older people. Included were
effects on general health, falls and fractures, driving, use of community
support services, admission to nursing homes, and on the risk of dying.
After taking into account age and other factors associated with a low self-rated health, people with visual impairment were around 20% more likely to rate their health at a lower level than those without impairment. People with visual impairment were also around 35% more likely to have hearing loss than those without visual impairment.
Community support services (meals on wheels, home care and home nursing) were used increasingly by older members of the population. After taking into account age and other factors associated with use of community support services, people with visual impairment were three time more likely to need such services. The increase was around 17% for each line reduced on the vision chart. This impact was greater for ‘younger' than ‘older' members of this community.
Nursing home admission is an important measure of increasing dependency and occurred in around 5% of people followed for 5 years after the first examination in the BMES. These admissions were confirmed by subsidy payments. After accounting for increasing age and the other factors associated with nursing home admission, people with visual impairment were around twice as likely to be admitted compared to those with normal vision. This impact was also greater for 'younger' than 'older' members of the community.
A further impact could be measured on the risk of dying among older participants. After taking into account increasing age and other factors found to predict mortality (diabetes, heart disease, smoking, etc), the presence of visual impairment at the baseline examination was associated with an 80% increased risk of dying during the 5-year period. The finding matched similar findings reported by the Melbourne Visual Impairment Project.
These impacts were almost always strongest for visual impairment not able to be corrected by refraction, indicating presence of eye disease. Importantly, however, a number of impacts also had a measured increase among people whose visual impairment was able to be corrected by a change in refraction or provision of new glasses.
