Low vision is a term used to describe a permanent and significant loss of visual function including either visual acuity (the ability to see detail), visual field (the ability to see a large area of about 175 degrees) or both. Low vision cannot be corrected with conventional glasses, contact lenses, surgery or medication.
Low vision is not to be confused with legal blindness which is defined in federal law for use by the Social Security Administration or Internal Revenue Service as “central visually acuity of 20/200 or less in the better eye after best possible standard correction or visual field of no greater than 20 degrees.”
A central visual acuity of 20/200 means that a person can only see visual detail such as a letter or word at a distance of 20 feet that can be seen by a normally sighted person at a distance of 200 feet.
Legal blindness is not necessarily the same as total blindness. All totally blind people are legally blind. Some legally blind persons that have some usable vision, are considered to have low vision. There must be some usable vision remaining in the eyes to be considered low vision.
To be eligible for special education, a pupil must have a visual impairment, which even with correction, adversely affects a pupil's learning of curriculum. For educational purposes, the term visually impaired includes: 1) functionally blind students who because of the severity of their visual impairment rely basically on senses other than vision as their major channels for learning; and 2) low vision students who use vision as a major channel for learning. A visual impairment does not include visual perceptual or visual motor dysfunction resulting solely from a learning disability.
O C.F.R. 404.1581 (1988)
Low vision may be genetic and begin at birth such as albinism; it may be developed during the lifetime due to such an eye disease as macular degeneration; or it may be caused by an accident, such as optic atrophy due to a brain injury. Some eye diseases, such as aniridia, are stable, while others progressively deteriorate, often resulting in low vision followed by total blindness such as diabetic retinopathy.
Low Vision Devices
Collaboration among all professional education and eye care staff in providing coordinated, comprehensive services is critical in achieving the greatest success for students with visual impairment.
Unfortunately, many eye doctors are not aware of the availability of devices designed to help low vision students use their residual vision more effectively. Not enough attention is focused on individuals with visual impairments because they comprise only a very small minority of the population that requires eye care.
Students with visual impairment and their families are often discouraged after being told by an eye doctor that no more can be done to help them use their residual vision more effectively. It is estimated that approximately .4 million persons in California have low vision. Only about 1 of 10 visually impaired persons are functionally blind and have no useful vision.
Showing students and their families nonprescription devices and materials as those contained in the ENVISION I & II kits from the American Printing House for the Blind (APH) will raise the level of awareness of the existence of a variety of low vision devices and provide the necessary motivation, and acceptance that something can be done in many cases.
Low vision devices work in one of several ways:
- Control the focus or image clarity
- Control illumination and contrast
- Control magnification or size of the image on the retina
Magnification can be achieved by:
- Relative distance (moving closer to the object)
- Relative size (physically enlarging the object)
- Optical (enlarging the image on the retina by passing it through a lens or group of lenses)
- Electronic projection magnification (enlarging the image on the retina, using projectors and/or computers)
Some generalizations about optical devices are:
- The larger the lens, the weaker the magnification
- The larger the area one sees at one time through the lens
- The larger the depth of focus that makes the working distance less critical
- The smaller the lens, the stronger the magnification
- The smaller the area one sees at one time through the lens
- The less the depth of focus that makes the working distance more critical
- The closer the lens is held to the eye, the greater the area the user will be able to see through the lens, regardless of the magnification
- Plastic is lighter than glass, but it scratches more easily
The low vision student should understand the characteristics—advantages and limitations—of the devices based on the following factors:
- Working distance
- Field of view
- Depth of focus
- Cosmetic appearance
- Style of the device (hand-held, head-borne, etc.)
The devices will be more readily accepted by the low vision student when:
- The device enables the student to do what he or she wants to do
- The device appears as conventional as possible so it doesn’t attract attention
- The device is easily portable so that it can be used wherever the student goes
- The student is highly motivated and believes success is possible
- There is follow-up training to reinforce successes as the student is learning to use the device effectively
The instructional model should include:
- Routine to establish a pattern
- Success-oriented training
- Short learning periods and that gradually increase in duration
- Use of relevant, age-appropriate, high-interest-level activities
Learning sequences vary, but generally with respect to magnifiers, the user should do the following:
- Locate the material to be read
- Adjust the angle of lighting
- Hold the device and position the material in such a way that a comfortable posture can be assumed, resulting in minimal fatigue
- Look through the center of the lens to minimize distortion
- Learn to read or scan by moving the head or the material or a combination of both
Learning sequences for monocular telescopes should include:
- Learning to locate stationary objects through the telescope while the student is motionless
- Learning to locate moving objects through the telescope while the student is motionless
- Learning to locate moving objects while the student is in motion
- Develop visual association, visual memory and spatial perception (where are the objects in space) so that the student can learn to cope with specific challenges, such as telescopic parallax, blind spots in the field, and speed blur
Other kinds of valuable nonprescription, low vision devices are various hand magnifiers, focusable stand magnifiers, loupes, head-borne nonprescription aids, clip-on loupes for near vision, and a large variety of other monocular and binocular distance-vision devices in various magnification ranges and styles to fit individual needs.
It is very important, whenever possible, to obtain a comprehensive low vision evaluation for all visually impaired students to ensure consideration of the widest possible variety of low vision devices. The comprehensive low vision evaluation will also provide important information to the teacher or mobility specialist about the student’s etiology, diagnosis, prognosis, stability of the eye disease, the refractive error, visual fields, and the adequacy of visual function.
In California, allowing students to try nonprescription magnifiers or monocular devices, or giving them other nonprescription devices without conferring with an eye doctor, does not constitute the practice of optometry.
Comprehensive Low vision Assessment
A regular eye exam concentrates on diagnosing eye disease and correcting visual acuity with regular lenses. A low vision exam focuses on using specialized low vision devices to enhance remaining vision when low vision cannot be restored to normal vision. The person with low vision requires a functional vision assessment to evaluate vision functioning and the effect it has on daily living activities, such as reading and moving about safely.
A comprehensive low vision assessment includes a multidisciplinary approach to vision services. The eye exam uses special techniques and equipment to assess visual functioning. It involves multiple visits and the exam takes longer to administer. In addition to services from an ophthalmologist and/or optometrist, a comprehensive low- vision exam team may commonly involve, but is not limited to, a psychologist, social worker, rehabilitation counselor, teacher, orientation and mobility instructor, and low- vision device technician. The purpose of the exam is to help people with low vision gain a sense of independence and learn to compensate for their vision loss. In order to conduct a comprehensive low vision assessment, there must be access not only to a multiple disciplinary team of professionals but also a large variety of low vision devices, including such optical devices as magnifiers and telescopes, non-optical devices (i.e.) writing guides, talking calculators, closed-circuit television, and computer screen readers.
Locating A Low vision Specialist in Your Area
Only about five percent of all eye doctors specialize in low vision. You may contact the American Foundation for the Blind (AFB) for information toll free at 800-232-5463. You may also contact the California Optometric Association toll free at 800-877-5738. The California Academy of Eye Physicians and Surgeons can be contacted toll free at 800-443-9370 to locate an eye doctor who specializes in low vision . A list of Optometrists who have earned special recognition as diplomats in low vision is available by contacting the American Academy of Optometry at 301-984-1441.
California Low vision Clinics and Centers
California Pacific Medical Center
P.O. Box 7999
San Francisco, CA 94120-7999
The Center for the Partially Sighted (CPS)
6101 W. Centinela Ave., Suite 150
Culver City, CA 90230
Jules Stein Eye Institute
University of California, Los Angeles
100 Stein Plaza
Los Angeles, CA 90024
Loma Linda University Medical Center
Dept. of Ophthalmology
11370 Anderson Street, Suite 1800
Loma Linda, CA 92354
Low vision Clinic
University of California, San Francisco
400 Parnassus Ave. 7th Floor
San Francisco, CA 94143
Low vision Clinic
School of Optometry
University of California, Berkeley
230 Minor Hall
Berkeley, CA 94720
Marin Low vision Clinic
Marin Senior Center - Whistlestop
930 Tamalpais Ave.
San Rafael, CA 94901
By Referral Of Eye Doctor Only
Optometric Center of Los Angeles
3916 South Broadway
Los Angeles, CA 90037
Vista Center for the Blind and Visually Impaired
2470 El Camino Real, #107
Palo Alto, CA 94306
SF Lighthouse for the Blind
Low vision Clinic
214 Van Ness Ave.
San Francisco, CA 94102
Scripps Memorial Hospital
Partial Vision Center
9888 Genesee Ave.
La Jolla, CA 92037
Society for the Blind
Low vision Clinic
1238 S Street
Sacramento, CA 95818
Southern California College of Optometry
Low vision Clinic
2575 Yorba Linda Blvd.
Fullerton, CA 92831
Byers Eye Institute
2452 Watson Court
Palo Alto, CA. 94303
Eye Laser Center: 650-498-7020
Eye Clinic: 650-723-6995
900 Blake Wilbur Drive #W3002
Palo Alto, CA 94304
University of California, Davis
Low vision Service
4860 Y Street, #2400
Sacramento, CA 95817
Vision Care Center
7075 North Sharon Ave
Fresno, CA 93720
Eye Care Center
Western University of Health Sciences
795 E. Second Street, Suite 2
Pomona, CA 91766
Other California Agency Links for Low vision Services
California Department of Rehabilitation
P.O. Box 944222
California Department of Social Services
Office of Services to the Blind
744 P Street, Mail Station (MS) 8-16-91
Sacramento, CA 95814
Additional National Low Vision Internet Resources
Note: The low vision clinics and Web resources listed here represent only a small sample of those available and does not constitute an endorsement or recommendation by the California Department of Education for any of their services or products.
Low vision Gateway
National Association for the Visually Handicapped
NYISE Low vision Resource Center