Introduction: What are visual impairments?
Visual impairment inckuding blindness is defined in the regulations accomplanying the Individuals with Disabilities Education Improvement Act of 2004 (PL 108-446) as "an impairment in vision that, even with correction, adversely affects an individual's educational performance. The term includes both partial sight and blindness" (34 C.F.R. 300.7 [c][13]).
Over the years, the term legally blind has been used as a federal definition of blindness. This definition involves using a Snellen chart, which is used to make a clinical measurement of the true amount of distance vision an individual has under certain conditions. A vision acuity of 20/200 or less in the better eye with correction or a visual field that is no greater than 20 degrees is the defintion of legally blind.
What are causes of visual impairment?
Refractive Errors
- Mytopia: commonly called near-sightedness; a student is able to read his textbook but has difficultiy seeing the chalkboard
- Hyperopia: commonly called far-sightedness; a student can see objects far away but has difficulty seeing them up close
- Astigmastism: an irregularity in the curvature of the cornea resulting in disorted or blurred vision
Defects of the Ocular Muscle
- Strabismus: an improper alignment or imbalance of the eyes, commonly referred to as crossed eye, which, left untreated, will cause pernament blindness
- Nystagmus: a rapid, involuntary movement of the eye
Disorders of the Cornea, Iris, or Lens
- Cataracts: a clouding of the lens of the eye resulting in blurred vision; may be corrected surgically
- Glaucoma: a build-up pf fluid pressure in the eye; central and peripheral vision may be permanently impaired
Other
- Retintis pigmentosa: a common hereditary condition, usually causes "tunnel vision" and night blindness prior to total blindness
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