Blindness and Visual Impairment

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Blindness and Visual Impairment

• Physical Disabilities, Rehabilitation and
  Employment
• BCE 542
• October 15, 2002

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Eye Structure

• Cornea A curved window at the front of the
  eye lets in light and protects the eye from
  foreign objects.
• Iris The colored part of the eye which will
  expand or contract according to light conditions.
• Pupil The opening in the cornea that admits
  light.
• Lens A transparent disk which focuses light to
  the retina becomes thicker or thinner according
  to near or far vision.
• 1) Aqueous and 2) Vitreous Humor Liquid chamber
  filling the 1) space between cornea and lens or
  2) space between lens and retina.
• Retina A light-sensitive lining of the eye that
  serves as the eyes picture screen.
• Macula The area of the retina on which the
  central visual field is focused the center of
  the macula is called the Fovea.
• Optic Nerve Transmits nervous signals from the
  retina to the occipital lobe of the brain (the
  rear portion of the brain) where they are sensed
  as images.

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Vision Problems

• Light Sensation
• Refraction
• Central Vision
• Night Vision
• Color Vision
• Binocular Vision/Depth Perception

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Definitions

• Visual Impairment Any abnormality in vision
  (color, light sensation, accommodation, central
  vision, etc.)
• Cecutiency Any visual impairment short of total
  blindness e.g., any visual impairment that still
  permits sensation of light. (Person with
  cecutiency is cecucient)
• Legal Blindness vision no better than 20/200 in
  the least affected of the two eyes (corrected
  vision) and/or the inability to perceive more
  than twenty degrees of the central visual field.
• Total Blindness Complete inability to sense
  light.

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Refractive Errors

• Myopia or Nearsightedness Lens focuses images in
  front of retina, individual has difficulty seeing
  objects at a distance.
• Hyperopia or Farsightedness Lens focuses images
  toward a point behind the retina person has
  difficulty seeing objects close to the body (such
  as in reading)
• Presbyopia (literally means old vision) Lens
  loses flexibility, causing problems in
  accommodating from near to far vision occurs
  with age. Calls for bifocals.
• Astigmatism Cornea or lens is out of round or
  shaped in a way that is out of sync with the rest
  of the eye causes a distortion of the visual
  image.
• Treatment
• Corrective lenses (glasses or contact lenses)
• Surgery (Radial Keratotomy, Astigmatic
  Keratotomy, LASIK)

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Eye Diseases and Disorders

• Bacterial Infections
• Glaucoma
• Cataract
• Retinopathies
• Retinitis Pigmentosa (RP)
• Macular Degeneration
• Nystagmus
• Strabismus

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Bacterial Infections

• Conjunctivitis Inflammation of the conjunctiva,
  or outer eye membrane.
• Trachoma Chronic bacterial infection of the eye
  can lead to blindness if not treated.
• Keratitis Inflammation of the cornea can cause
  severe scarring of the cornea if not treated
  also, very painful.

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Glaucoma

• Rise in pressure in the eye caused by increase in
  the volume of the aqueous humor. Two types
• Chronic Open Angle Glaucoma (Simple Glaucoma)
  Gradual reduction in outflow of aqueous humor
  over a period of years.
• Acute Closed-Angle Glaucoma Rapidly developing
  form severely painful requires prompt medical
  attention to save sight.
• Pressure eventually damages optic nerves, causing
  cupping of nerve. This results in a loss of
  peripheral vision and gradual narrowing of the
  visual field to slits, then total blindness.
• Treatment
• Drugs are available to treat simple glaucoma.
  Acute closed angle glaucoma usually requires
  surgical correction--quickly.

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Cataract

• A clouding of the eye lens caused by injury,
  aging, or substances such as steroids.
• Treatment involves removal of the natural lens
  and implantation of an artificial lens or
  prescription of special eyeglasses.

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Retinopathies

• Deterioration of the retina.
• Most common is Diabetic Retinopathy, in which the
  small blood vessels (capillaries) of the retina
  burst as a result of diabetes, affecting normal
  eye function.
• Laser surgery may provide minor help to diabetic
  retinopathy, but damage is largely irreversible.
  
• Best treated through prevention--management of
  diabetes.

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Retinitis Pigmentosa (RP)

• Degeneration of the pigments of the retina.
• Congenital Disorder that progresses slowly over
  time.
• Individual loses night vision at first, then
  gradually loses peripheral vision, then becomes
  totally blind, usually by the fifth decade of
  life.
• No treatment and no cure.

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Macular Degeneration

• Degeneration of the macula, the part of the
  retina on which the lens focuses light.
• Eventually leads to loss of central vision,
  although peripheral vision is unaffected.
• Individual cannot see what the eye is focused on.
• Usually a disorder of older persons.
• No treatment or cure.

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Nystagmus

• An involuntary movement of the eyes that may be
  congenital or may be brought on by a number of
  neurological causes (such as Menieres Disease,
  discussed under hearing disorders).
• May cause difficulty in eye focus.
• Removal of underlying neurological cause may
  eliminate the disorder

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Strabismus

• Crossed-Eyes
• The two eyes cannot focus on one object.
• Usually present from an early age and can result
  in unequal vision in the two eyes (lazy eye or
  suppression amblyopia).
• Can be treated by drugs, surgery, lenses
  treatment should begin early in life.

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Other eye problems

• Eye injuries Can cause scar tissue to develop in
  the eyes.
• An injury to one eye that causes blindness often
  causes the other eye to react in sympathy.
• Retinal Detachment Retina becomes detached from
  the rest of the eye results in loss of field of
  vision or blindness if not treated.
• Floaters Pieces of eye tissue break off from
  retina and float in the vitreous humor. Common
  in persons who are severely nearsighted. Usually
  not a problem unless they are very large.
• Binocular vision responsible for depth
  perception a problem in persons who are sighted
  only in one eye.
• Color Blindness
• Usually not a big rehabilitation concern--few
  jobs require extreme color vision.
• Most common Red-green color blindness.
• Most rare Monochromatic Vision.
• Much more common in men than in women.

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Rehabilitation and Visual Impairments

• First Step Understand the persons residual
  visual capacity.
• Total Blindness Individuals will have no
  capacity to interpret any type of visual stimuli.
• Cecutiency Individuals may retain some degree of
  vision that will affect their functioning in
  different ways in different environments.
• Differences in functioning according to
  environment may lead some to think that
  individual is malingering in some situations.

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Rate of vision loss

• Congenital Individuals tend to develop survival
  skills quickly as a part of normal development.
• Sudden loss of vision Grieving process, trauma.
  Individual does have advantage of knowing the
  extent of vision loss. Requires immediate
  adaptation.
• Gradual loss of vision Individuals can gradually
  develop greater adaptive skills as disease
  progresses. Individual does not know how far
  vision will deteriorate, however, and may be
  reluctant to give up old ways (denial).

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Mobility Issues

• Rehabilitation Teachers Individuals who teach
  mobility to individuals who are blind.
• Long Cane--used by most persons who are
  blind/visually impaired as a mobility aide. Must
  be careful of overhangs.
• Guide Dogs/Seeing-Eye Dogs Not used by the
  majority of persons who are blind/visually
  impaired.

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Communication Issues

• Visual stimuli must be communicated through
  another means, usually aural/hearing.
• Talking books
• Tape recorders
• Talking appliances (computers)
• Braille
• Only a minority of persons who are blind/visually
  impaired can read/write in Braille.
• Person must have sensation in fingers for Braille
  usage.
• Large Print Materials/Optical Expansion Equipment
• Can be of assistance for higher functioning
  persons with severe visual impairments.

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Occupational Issues

• Traditional jobs for persons with visual
  impairments
• Dark Room workers
• Piano Tuners
• Nothing wrong with these, but more options now
  available.
• Vocational options will depend upon the ability
  to modify an occupation so that the individual
  can perform it safely and efficiently.
• Assistive Technology/Job Modification are
  critical.
• Other rehabilitation issues (independent living,
  transportation, etc.) will need to be addressed
  so that the individual with a visual impairment
  can sustain employment.