Low vision is a bilateral impairment to vision that significantly impairs the functioning of the patient and cannot be adequately corrected with medical, surgical, therapy, conventional eyewear or contact lenses. It is often a loss of sharpness or acuity but may present as a loss of field of vision, light sensitivity, distorted vision or loss of contrast.
Low vision often may occur as a result of birth defects, injury, the aging process or as a complication of disease. Inspite of tremendous advances in medical science, many patients end up with poor vision or blindness, due to a variety of causes. It is not unusual for people with vision loss to experience different levels of concern, anxiety or frustration or to struggle with lifestyle adjustments as their disease progresses.
A low vision evaluation should mainly include determination of the patient's goals, complete visual function evaluation and ocular health assessment. The examination begins with an extensive history. Special emphasis is placed on the functional problems of the patient including such items as vision to read, functioning in the kitchen, television viewing, school requirements, etc. Preliminary test may include assessment of ocular functions such as depth perception, color vision, contrast sensitivity, curvature of the front of the eye. Careful measurements is done by the visual acuity low vision test.
Low vision rehabilitation is a service that helps patients to optimize their visual function and maximize their quality of life. Low Vision services do not cure the cause of the vision problem but rather utilize the remaining vision to its fullest potential. Low vision care does not replace the need for other concurrent treatments such as laser, medication and surgery.
Low vision doctors prescribe prescription eyewear, filters, microscopic - telescopic eyewear, magnifiers, adaptive equipment, closed circuit television systems, independent living aids, training and counsel patients.
Magnification is a major tool of low vision rehabilitation. The lower power magnifier will have a larger diameter or field of view but but will create a smaller image. A higher power magnifier will have a smaller field of view but the image will be larger. Magnifiers with brighter halogen and xenon illumination often improve reading, particularly in age related macular degeneration patients.
Strong bifocals, dedicated reading glasses and microscopic eyewear may improve reading. To magnify distance objects, telescopic systems are frequently used. These may be handheld or mounted in eyewear called bioptics. Telescopes may be attached to prescription eyewear to create what is called a bioptic system.
Closed circuit television systems are capable of higher levels of magnification and can manipulate the brightness and contrast of the image. The concept of a CCTV is simple. A video camera is used in real time to capture the image of the reading material and display it on a monitor. For example, the poor contrast of newspaper print can be enlarged 40 times. New innovations in CCTV technology are expanding their use and availability.
Patient acceptance in using devices is very important. It may depend on their willingness to hold reading materials close.