Low vision and vision loss could be defined as best corrected vision which is insufficient to do what you want to do. There are two parts to the definition:
The Vision: best corrected with conventional spectacles or contact lenses. The Task: activities that you want to do but are now difficult or impossible. For example, activities include reading, writing, driving, television, playing cards, or seeing medication bottles.
For a person to benefit from Low Vision Care there must be a degree of usable vision and a goal to do a visual task. IALVS doctors discuss these issues in a free telephone interview before an appointment is offered.
Download our low vision exam fact sheet
Who gets Low Vision?
Vision loss can occur from medical conditions, degenerative changes, congenital or genetic defects, and traumatic injuries. While most vision loss occurs in people over 65, low vision can occur at any age.
Most conditions that cause irreversible vision loss do not cause complete and total blindness. Usually a person is left with “residual” vision that can be useful, especially with the help of low vision doctors. Low vision doctors of IALVS are uniquely trained and experienced in providing low vision glasses and devices plus rehabilitation training to make the most of the vision that remains.
Causes of Low Vision
Some of the major causes of vision loss are age related macular degeneration, diabetic retinopathy, inoperable cataracts, and open angle glaucoma. Each is described below:
Macular Degeneration & Diabetic Retinopathy
Age related macular degeneration is the leading cause of vision loss in those over 65. By definition, macular degeneration affects only the macular portion of the retina. The retina, like film in a camera, is the photosensitive layer of the eye. It is “wall-papered” to the back of the eye and is extremely thin. The macular portion of the retina, a very small area, is the part we use for sharp, clear central detail vision. The rest of the retina, the peripheral or side vision retina, is used for mobility and detecting motion.
When the macula degenerates, whether it’s wet or dry, only the central vision is reduced. The side vision always remains. Always.
Atrophic (dry) macular degeneration is when the cells in the macular die. Causes can be aging, nutrition, sunlight, smoking, genetics and other causes we may not know about yet. There is simply no medical treatment. Dead retinal cells cannot be brought back to life. Retinal cells cannot be regrown, replaced, moved or transplanted.
Exudative (wet) macular degeneration is caused by leakage of fluid from the blood vessels behind the macula. Because the macula has its own blood supply, only the macular area is affected. The peripheral retina has another blood supply.
Treatment with injections is aimed at stopping the leak. These injections are called angiogenesis inhibitors. The two most commonly used are Lucentis and Avastin.
The Technical Explanation
Vision loss in wet AMD is caused by the growth of abnormal leaky blood vessels that eventually damage the macula. Angiogenesis inhibitors are antibody fragments that bind to and inhibit the activity of human vascular endothelial growth factor (VEGF), a protein believed to play a critical role in the formation of these new blood vessels. The drug is injected into the vitreous portion of the eye (the clear jelly-like substance that fills the eye).
Diabetic retinopathy is a leading cause of blindness in American adults. It is caused by changes in the blood vessels of the retina. In people with diabetes for many years, blood vessels may swell and leak fluid or abnormal new blood vessels grow on the surface of the retina. If you have diabetic retinopathy, at first you may not notice changes to your vision. But over time, diabetic retinopathy can get worse and cause vision loss. Diabetic retinopathy usually affects both eyes.
Diabetic retinopathy has four stages:
- Mild Nonproliferative Retinopathy. At this earliest stage, small areas of balloon-like swelling in the retinas tiny blood vessels called micro aneurysms occur.
- Moderate Nonproliferative Retinopathy. As the disease progresses, some blood vessels that nourish the retina are blocked.
- Severe Nonproliferative Retinopathy. As more blood vessels are blocked, several areas of the retina are denied their blood supply. The retina compensates by growing new blood vessels. This is called neovascularization.
- Proliferative Retinopathy. The new blood vessels are abnormal, fragile and grow along the retina and along the surface of the clear, vitreous gel that fills the inside of the eye. Because they have thin, fragile walls they can leak blood causing severe vision loss and even blindness.
A cataract is a clouding of the normal crystalline lens located in the eye. Most cataracts are related to aging and are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery. A cataract can occur in either or both eyes, but cannot spread from one eye to the other.
The lens is a clear structure located behind the pupil and helps to focus light on the retina. In a normal eye, light passes through the transparent lens to the retina. The image is then changed into electrical nerve signals by the retina and is sent to the brain. The lens must be clear for the retina to receive a sharp image. When the lens becomes cloudy, which is called a cataract, the image you see will be blurred and/or hazy.
Treatment is by surgical extraction of the lens with replacement of a plastic implant. For the most part, cataract surgery is extremely successful and results in virtually normal vision.
However, there are times when cataract extraction can exacerbate macular degeneration or cause macular edema resulting in increased vision loss.
Talk to your eye care professional about these risks. Second opinions are often helpful and IALVS doctors are happy to help you make sure that cataract surgery is right for you.
Glaucoma is actually a group of diseases that can damage the eye’s optic nerve resulting in vision loss and even blindness. Glaucoma occurs when the normal fluid pressure inside the eyes slowly rises. Usually there are no symptoms, which is why glaucoma is called the silent thief of sight. However, with early treatment, you can often protect your eyes against serious vision loss.
There are many types of glaucoma including open angle, closed angle, congenital, and secondary. The most common type, open angle, has no symptoms. There is no pain, redness, swelling, tearing or other signal to tell you of the problem. The vision loss is so gradual, beginning in the periphery or in the normal blind spot that people do not notice until significant loss occurs.
Studies have shown that the early detection and treatment of glaucoma, before it causes major vision loss, is the best way to control the disease. IALVS doctors recommend an annual dilated eye examination for early detection.