Visual Impairment Factors Affecting Visual Function and Their

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