What You Need to Know About Low Vision
Low vision is a complex area within the field of visual impairments. Individuals with low vision can have very different amounts of vision and ways of seeing. The purpose of the following information is to help teachers better understand the area of low vision and to introduce terms and definitions commonly associated with low vision.
A child with low vision may experience difficulty in acquiring concepts. Vision is an organizing sense that allows us to perceive objects at a distance and to make connections between these objects. Many concepts developed in childhood are learned incidentally through vision. If the visual sense is impaired, concepts may be incompletely developed or missed entirely. Because of this, it is important for children with low vision to directly experience as much of their world as possible and to receive augmented instruction in making connections between objects and processes. (See the Resources below.)
Low vision terms
Much confusion exists in the terminology surrounding low vision. Often times, individuals may use the terms partially sighted, legally blind, blind, and low vision interchangeably. Although out of date, the term partially sighted refers to individuals with visual acuities ranging from 20/70 to 20/200. For example, a student with acuity of 20/100 is able to see at 20 feet what an individual with 20/20 visual acuity sees at 100 feet. Legal blindness refers to individuals with central visual acuities of 20/200 or less in the better eye with the best possible correction, or with visual fields of 20 degrees or less. Blindness is a more general term used to describe a person with a significant loss of vision, usually in the range of 20/200 or less. Often times, the term is used to explain an individual with very little or no functional use of vision. Low vision is a term related not only to visual acuity but often includes an individual's level of visual functioning. A precise definition for an individual with a visual impairment who is not functionally blind is an individual who has "difficulty accomplishing visual tasks, even with prescribed corrective lenses, but who can enhance his or her ability to accomplish these tasks with the use of compensatory visual strategies, low vision and other devices, and environmental modifications" (Corn and Koenig, 1996).
Of the total population of individuals with visual impairments, approximately 90 percent have some functional vision. This means that just 10 percent of individuals with visual impairments are not able to use their vision in some way to complete daily tasks.
Common Causes of Low Vision
Following are some of the most common causes of visual impairment.
Albinism - results from a lack of pigment. Some forms of albinism affect only the eyes (ocular) while other forms affect skin and hair color as well as the eyes (oculocutaneous). Albinism is hereditary and may be autosomal recessive or X-linked.
Aniridia - the partial or total absence of the iris of the eye. The lack of an iris results in acuity loss, light sensitivity, and visual field loss.
Aphakia - the absence of the lens of the eye. The lack of a lens prevents the ability to adjust focus between objects at different distances.
Cataracts - result of the lens of the eye becoming cloudy or opaque. The clouding can occur over the entire lens or over a small area over the lens. Surgical removal of the cataract can result in aphakia.
Coloboma - a birth defect occurring during the development of the fetus. The result is underdevelopment, which results in a cleft in the pupil, iris, ciliary body, lens, retina, choroid or optic nerve.
Glaucoma - a condition resulting from an increase of pressure inside the eye, often from improper drainage of fluids. Increased pressure can cause damage to eye structures such as the optic nerve.
Macular Degeneration - the gradual loss of sensitivity of the central portion of the retina. Because this is the area of the retina responsible for detail vision, macular degeneration is often associated with the loss of central vision and the ability to see fine detail.
Nystagmus - the involuntary movement of the eyes resulting in the inability to maintain a steady fixation. The movement can be horizontal, vertical, circular, or mixed.
Optic Atrophy - degeneration of the optic nerve. Loss of function of the optic nerve results in a decreased ability to transmit electrical signals to the visual center of the brain.
Optic Nerve Hypoplasia - a condition in which the number of nerves within the optic nerve bundle is reduced.
Retinitis Pigmentosa - a progressive degeneration of the retina resulting in night blindness and peripheral field loss.
Retinopathy of Prematurity - a condition in which the normal growth of blood vessels in the retina is disturbed during fetal development, often due to circumstances surrounding premature birth. This condition can lead to an increased risk of retinal tears or retinal detachment.
Common Myths Surrounding Individuals with Low Vision
Many myths exist surrounding low vision. The following are just a few.
- Anyone with a visual impairment, especially if they are identified as "legally blind," uses a white cane and is not able to live independently.
A person with low vision might find using a white cane useful in some situations but many do not need a cane at all. No matter what level of vision a person has, it is not a barrier to living a free and independent life.
- Individuals with low vision are unable to drive.
In fact, over 25 states allow persons with low vision to earn their driver's license. Eligible individuals may have restrictions on their license and/or may be required to utilize a bioptic telescopic system when behind the wheel. Eligibility requirements vary by state, but may require the individual to have visual acuity of 20/200 or better and/or full visual fields.
- Individuals with low vision are unable to read regular print, reading Braille instead.
While some with low vision might read Braille, they might also read large print, or even read regular print with the use of an optical device.
- Individuals with low vision do not need Orientation and Mobility instruction.
Anyone who has a visual impairment would most likely benefit from travel instruction. Being able to make the most out of what visual cues a person can see, being able to understand how complex systems like traffic intersections work, and developing the spatial reasoning used to navigate in the world are all examples of skills and concepts that a person with low vision might need assistance in acquiring or refining.
Doctors Involved in the Care of Children with Low VisionIt is not uncommon for students with visual impairments to see several different types of eye specialists in their life. This may be confusing not only for parents and their children, but also for administrators who are required to document eligibility for services with certain medical reports. Teachers of students with visual impairments also rely on different doctors to provide them with various pieces of information.
Optometrists: Doctor of optometry (OD) specializing in vision problems, treating vision conditions with glasses, contact lenses, and low vision aids. Optometrists, especially those specializing in low vision, often prescribe a wide range of optical devices for near a distance use including magnifiers, telescopes, and bioptic telescope systems.
Ophthalmologists: Physician (MD) specializing in diagnosis and treatment of refractive, medical, and surgical problems related to eye diseases and disorders.
Low Vision Specialists: Usually an optometrist who specializes in low vision but can also be used to refer to educational professionals certified in instructing persons with low vision.
Opticians: Professional who makes and adjusts optical aids, e.g., eyeglass lenses, from refraction prescriptions supplied by an ophthalmologist or optometrist.
Students with low vision are a diverse group of individuals. This fact sheet barely touches the tip of the iceberg. The following resource will be helpful in your search for more detailed information.
Related Publications from AFB Press
Holbrook, M.C. & Koenig, A.J. (2000). Foundations of education: History and theory of teaching children and youths with visual impairments. New York: American Foundation for the Blind.
Ferrell, K.A. (1984). Parenting preschoolers: Suggestions for raising young blind and visually impaired children. New York: American Foundation for the Blind.
Jose, R. T. (1983). Understanding low vision. New York: American Foundation for the Blind.
Lewis, S. & Allman, C.B. (2000). Seeing eye to eye: An administrator's guide to students with low vision. New York: American Foundation for the Blind.
Cassin, B. & Solomon, S.A.B. (1997). Dictionary of eye terminology. Gainesville, Florida: Triad Publishing Company.
Holbrook, C. (1996). Children with visual impairment: A parents' guide. Bethesda, MD: Woodbine House, Inc.
Levack, N. (1991). Low Vision: A resource guide with adaptations for student with visual impairments. Austin, Texas: Texas School for the Blind and Visually Impaired.
Web Site Addresses
All About Vision-Information on Low Vision: www.allaboutvision.com/lowvision
American Foundation for the Blind: www.afb.org
American Optometric Association: www.aoanet.org
American Printing House for the Blind: www.aph.org
Blind Children's Center Publications: www.blindcntr.org/pubs.htm
Low Vision Gateway: www.lowvision.org
National Association of Parents of Children with Visual Impairments: www.NAPVI.org
National Eye Institute (part of the National Institute for Health): www.nei.nih.gov/
National Organization for Albinism and Hypopigmentation: www.albinism.org
Texas School for the Blind and Visually Impaired/site links to low vision and eye disorders: www.tsbvi.edu/othersites.htm#Disorders
Texas School for the Blind and Visually Impaired/site links for parents and families: www.tsbvi.edu/othersites.htm#Parents
V.I. Guide: www.viguide.com