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 better-seeing 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

No cataract

cataract

Cataracts

No cataract

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