Visual Impairment

Medical and Psychosocial Aspects of Disability

Introduction

• Vision impairment affects a significant proportion of middle-aged and older Americans – 1 in 6 adults (17%), age 45 and older, representing

13.5 million Americans, reports some form of vision impairment even when wearing glasses or contact lenses

• The prevalence of visual impairments increase with age – 15% of people 45-64 – 17% of people 65-74 – 26% of people 75 and older

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 – Scotoma - loss of vision in an area

• 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.

• US Definition: Best-corrected visual acuity of 6/60 or worse (<20/200) in the better-seeing eye.

OR • Peripheral visual field is restricted to 20° or

less in the widest meridian of the better eye • (US Definition of Low Vision: best-corrected visual acuity of 6/12

(<20/40) in better-seeing eye.)

Statistics

• In 2000 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 2000

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.

The Eye Diseases Prevalence Research Group, Arch Ophthalmol 2004;122:477-485.AMD=age-related macular degeneration, DR=diabetic retinopathy

Causes of blindness (best-corrected visual acuity <6/60 [<20/200] in the better-seeing eye) by race/ethnicity

.

The Eye Diseases Prevalence Research Group, Arch Ophthalmol 2004;122:477-485.AMD=age-related macular degeneration, DR=diabetic retinopathy

Causes of low vision (best-corrected visual acuity <6/12 [<20/40] in the better-seeing eye, excluding those who were categorized as being blind by the US definition) by

race/ethnicity

Prevalence of Blindness by Age and Race (US)

White Black Hispanic

40-49 0.12 0.18 0.05

50-54 0.10 0.34 0.10

55-59 0.11 0.52 0.16

60-64 0.15 0.81 0.26

65-69 0.23 1.25 0.41

70-74 0.43 1.93 0.64

75-79 0.93 2.96 0.99

>80 6.82 6.85 2.42

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 – Approximately 50% of Americans

between 65 and 74 and 70% over age 75 have cataracts

• 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 • The greater the progression of the

cataract, the greater the visual impairment from the effects of glare, loss of contrast, and decreased visual acuity

• Normally, cataracts are successfully treated with surgery

• Assuming no complications, there should be no vocational implications following cataract surgery

No cataract cataract

Corneal Disease• The cornea is a structure that is prone to dystrophies, deposition,

noninflammatory progressive thinning (keratoconus), infection, viral diseases, and trauma

• 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 • Vocational Implications

– Vocational goals will be dependent on the degree to which the retinal image is compromised

Macular Degeneration• Macular degeneration is caused by

degenerative changes to the macular area of the retina that result in atrophy, hemorrhage, exudates, fibrovascular scars, or cyst formations

• 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, a decrease in color recognition, a loss of contrast, or an absolute or relative area of no vision (scotoma)

– Reading may become increasingly difficult and driving may have to be discontinued

Macular Degeneration• Treatment

– Laser treatment can sometimes be used to slow the progression of the disease

– Other treatments that have been investigated (but not yet established) include the use of radiation, laser treatment of drusen (small globular pathological growths formed on optic papilla or on Descemet's membrane), photodynamic therapy, submacular surgery, retinal cell transplantation, and the use of vascular endothelial growth factor

• Vocational Implications – Driving – Vision rehabilitation program may be needed before being able to

return to work • Accommodations/Assistive Technology

– Lenses and magnification devices – Talking books – Bold, felt-tip pens – Talking clocks (and other talking devices and appliances)

Diabetic Retinopathy• Diabetes accounts for about

5,000 new cases of blindness each year and people with diabetes have a 25 times greater risk for blindness than the general population

– 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

– May have transient episodes of diplopia

Diabetic Retinopathy

• Vocational Implications – Rehabilitation considerations must

include not only vision but also the effect of diabetes on other systems

• Accommodations/Assistive Technology – Low-vision devices – Prisms to correct transitory diplopia

Glaucoma• If left untreated, results in the destruction of the

peripheral retina • 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, especially if left untreated, irreversible optic nerve and visual field damage will occur, impairing night vision, visual acuity, mobility, and reading skills

Glaucoma• Treatment

– Medications that decrease production of aqueous humor or facilitate outflow of fluid

– Laser surgery to create drainage holes – Other surgery procedures to assist with drainage

• Vocational Implications – Progressive loss of vision may result in difficulty in

performing one's job • Accommodations/Assistive Technology

– Low-vision devices, including spectacles, hand and stand magnifiers, closed circuit TV, and lighting

– Absorptive lenses enhance the apparent brightness of the scene and often aid in mobility

– Modifications in the work space may be required, with high technology, including voice-output devices

Albinism• Albinism is a trait that is inherited through autosomal

recessive or sex-linked transmission and results in characteristics that affect the pigmentation of the skin and hair as well as the iris and retina

• Persons with albinism have a decrease in visual acuity due to macular aplasia

• Treatment consists of corrective spectacle lenses as well as absorptive lenses to reduce light sensitivity

• Vocational Implications – Similar to other types of visual impairments – Need to pay attention to exposure to sunlight

• Accommodations/Assistive Technology – Low-vision devices, including strong microscopic reading

lenses, magnifiers, absorptive lenses, and telescopic lenses

Retinitis Pigmentosa• A progressive eye disease that

affects the pigmentary layer of the retina, and most commonly affects the periphery or midperiphery of the retina

• Most common cause of inherited blindness

• In addition, 30% of people with RP report some degree of hearing loss

• 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• Treatment

– At present, no medical or surgical treatments are known to stop or decrease the progression of RP

– Refractive corrections are necessary, along with absorptive lenses to cut down the glare or light sensitivity

– Contrast-enhancing lenses may be beneficial in enhancing performance and reducing adaptation times between outdoors and indoors

• Vocational Implications – Individuals with severe progressive visual field loss should not

contemplate occupations that will necessitate driving • Accommodations/Assistive Technology

– Closed-circuit TV to enable the person to control the brightness and contrast of the image viewed

– Prism lenses to increase the awareness of the periphery – The Nightsope might be able to be used for mobility under dim

illumination – Mobility devices, such as a traveling cane, special laser cane,

sensory device, or Seeing Eye dog

Peripheral Visual Field Loss from Strokes or Tumors • A person who has a stroke or tumor can be left with a

resultant visual field loss • In addition, can affect perception of visual form, color,

object meaning, recognition, and attention • May also be disorders of the visual system such as

hallucinations • Vocational Implications - driving • Accommodations/Assistive Technology

– Prisms to enhance spatial awareness – Mirrors to facilitate peripheral field awareness – Low-vision devices

General Vocational Implications• Transportation issues need to be

considered

• Safety issues need to be considered

Resources• The National Society to Prevent Blindness

(www.eyeinfo.org/national.html) • Prevent Blindness America (http://www.preventblindness.org/) • Prevent Blindness Florida (www.preventblindness.org/florida/) • American Academy of Opthamology (http://www.aao.org/) • Glaucoma Research Foundation (http://www.glaucoma.org/) • Lighthouse International (http://www.lighthouse.org/) • AMD Alliance International (http://www.amdalliance.org/) • National Eye Institute (http://www.nei.nih.gov/) • National RP Foundation (www.rpsa.org.za/training.htm) • Research to Prevent Blindness (http://www.rpbusa.org/) • The Rehabilitation Research and Training Center on Blindness and

Low Vision (http://www.blind.msstate.edu/) • Florida Division of Blind Services (www.state.fl.us/dbs/index.shtml) • JAN's webpage (www.jan.wvu.edu/media/sight.html)