Visual
Impairment
Factors Affecting Visual
Function and Their Treatment
• Visual Acuity - ability to see "detail"
– Measured using testing distance/letter size
– Normal is 20/20
– Limitation on acuity level is generally determined
by the spacing of the cones
– Treatment: glasses or some form of magnification
• Visual Field - a person's peripheral vision
• Contrast
• Lighting and Glare
– Often, too much light can be as detrimental as not
enough
Definition of Legal
Blindness
• WHO Definition: Best-corrected visual
acuity of less than 6/120 (<20/400) in the
better-seeing eye.
• WHO?
• US Definition: Best-corrected visual acuity
of 6/60 or worse (<20/200) in the betterseeing eye.
Statistics
• In 2010 there were 937,000 blind
Americans older than 40 (0.78%)
• 2,400,000 with low vision (1.98%)
• Thus, there were 3.3 million
Americans aged 40 or more with a
visual impairment in 2010
The Eye Diseases Prevalence Research Group (2004). Causes and prevalence of
visual impairment among adults in the United States. Archives of Ophthalmology,
122, 477-485.
Cataracts
• A cataract is opacity or clouding of
the lens that may develop as a
result of aging, trauma, hereditary
factors, birth defects, or diabetes
• Cataracts are a normal part of
aging
• Prevalence factors
– Caucasians are three times as
likely as African-Americans to
develop cataracts
– Smokers have a 60% increase
– Those taking medication for
gout are twice as likely to
develop cataracts
cataract
No cataract
Cataracts
cataract
No cataract
Corneal Disease
• Interference with corneal integrity can result in a
blurred or distorted image on the retina
– May experience severe glare, cloudy vision,
and reduced acuity
• Treatment
– Keratoplasty is the primary method of
restoring vision for an individual with a
diseased, irregular, or scarred cornea procedure involves transplanting a healthy
cornea from a compatible donor
– Recently, lasers have been used to treat
some corneal problems
Corneal Disease
Corneal Disease
Corneal Disease
Macular Degeneration
• Risk factors
– Caucasian
– Family history
– High blood pressure or a
history of hypertension
– Light iris color
– Smoking
• Functional Presentation
– Visually manifested as
distortions, a decrease in the
visual acuity
– Reading may become
increasingly difficult and
driving may have to be
discontinued
Macular Degeneration
Diabetic Retinopathy
• Diabetes accounts for about
5,000 new cases of
blindness each year
– Approximately 40% of
people with diabetes
have diabetic retinopathy
• Functional Presentation
– Fluctuating or severely
decreased visual acuity
– Problems due to glare,
reduced contrast
sensitivity, and various
types of visual field
problems
Diabetic Retinopathy
Glaucoma
• Basically three types of glaucoma
– Chronic open-angle glaucoma: elevated pressure
over time eventually affects the optic nerve and
visual field
– Acute (closed-angle) glaucoma: rapid increase or
spiking of the intraocular pressure that may be
accompanied by intense pain and even nausea or
vomiting
– Low-tension glaucoma: may be caused by a
decrease in blood flow to the optic nerve
• Over a period of time; irreversible optic nerve and
visual field damage will occur, impairing night vision,
visual acuity, mobility, and reading skills
Glaucoma
Glaucoma
Glaucoma
Retinitis Pigmentosa
• A progressive eye disease that affects the
pigmentary layer of the retina
• Most common cause of inherited blindness
• Functional Presentation
– Night vision and peripheral vision go hand
in hand - the more advanced the RP, the
greater loss of peripheral vision and the
more difficult to travel
– Reading becomes more and more difficult
as the visual field becomes small
– Glare or light sensitivity is frequently
associated with RP
Retinitis Pigmentosa
Stargardt’s Macular
Dystrophy
• Functional
deficits
– Causes central
detail vision loss
– Peripheral vision
is intact
– Eccentric viewing
is key to
improving visual
function
• Practical
application
– Eccentric fixation
training
– Low Vision
Devices
Stargardt’s Macular
Dystrophy
• The further out
from the macula
the scarring
extends, the
worse the
resulting
visual acuity.
Stargardt’s Macular