Visual Impairment

Children With Developmental Challenges 3(2+1)

Lesson 11 : Sensory Impairment – Visual

Visual Impairment

A visual impairment occurs when any part of the optical system is defective, diseased, or malfunctions. If the visual impairment is the result of a defective part (or parts), it is usually present at birth (congenital). These include missing parts (e.g., absence of an iris; absence of the eyes themselves), defective systems (e.g., dislocation of the lens; holes in the retina; drainage systems that are stopped up), and hereditary conditions (e.g., refractive errors due to eyeballs that are too short or too long; improperly shaped corneas; albinism).

“Visual impairment” including blindness means impairment in vision that, even with correction, adversely affects a child's educational performance. The term includes both partial sight and blindness. Visual impairment for any child means:

  1. A visual impairment, not primarily perceptual in nature, resulting in a
    measured visual acuity of 20/70 or poorer in the better eye with correction; or
  2. A physical eye condition that affects visual functioning to the extent that special education placement, materials and/or services are required in an educational setting.


The terms partially sighted, low vision, legally blind and totally blind are used in the educational context to describe students with visual impairments.

  • Partially sighted" indicates some type of visual problem has resulted in a need for special education.
  • “Low vision" generally refers to a severe visual impairment, not necessarily limited to distance vision. The child who has low vision may use a variety of optical devices (e.g., telescopes, special glasses, or magnification), but is primarily a visual learner; print of some size will probably be the preferred reading medium.
  • "Legally blind" indicates that a person has less than 20/200 vision in the better eye or a very limited field of vision (20 degrees at its widest point).
  • Totally blind students learn via Braille or other non-visual media.

The most prevalent eye diseases are age-related macular degeneration, cataracts, diabetic retinopathy, retinitis pigmentosa, and glaucoma. Other vision impairments may be the result of night or color blindness, myopia (nearsightedness), astigmatism (irregular curvature of the cornea), hyperopia (farsightedness), and presbyopia where the eye lens becomes elastic.

Last modified: Tuesday, 10 April 2012, 8:11 AM