Visual Impairment. Factors Affecting Visual Function and Their Treatment Visual Acuity - ability to...
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![Page 1: Visual Impairment. Factors Affecting Visual Function and Their Treatment Visual Acuity - ability to see "detail" –Measured using testing distance/letter.](https://reader030.fdocuments.net/reader030/viewer/2022032415/56649efd5503460f94c10843/html5/thumbnails/1.jpg)
Visual Impairment
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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
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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 better-seeing eye.
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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.
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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
No cataract
cataract
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Cataracts
No cataract
cataract
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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
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Corneal Disease
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Corneal Disease
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Corneal Disease
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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
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Macular Degeneration
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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
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Diabetic Retinopathy
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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
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Glaucoma
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Glaucoma
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Glaucoma
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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
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Retinitis Pigmentosa
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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
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Stargardt’s Macular Dystrophy
• The further out from the macula the scarring extends, the worse the resulting visual acuity.
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Stargardt’s Macular