Diseases and your vision
Glaucoma Diabetic retinopathy Retinitis pigmentosa Cataracts
- In macular degeneration the cells of the macula – the most sensitive part of the retina, the tissue that lines the back of the eye and sends visual signals to the brain. – start to break down and lose your ability to create clear visual images.
- The most common form of macular degeneration is age-related macular degeneration (AMD). Usually related to aging, AMD is the single largest cause of legal blindness in patients over 55 years of age. There are, as well, juvenile forms of macular degeneration or dystrophies including Stargardt’s Disease and Best’s Disease.
- The central part of the retina, also known as the macula, has the highest concentration of light sensitive cells and therefore is capable of the most detailed vision, which we use for reading, writing, driving and many other tasks that require detail. To use this part, we must look straight at an object. The more peripheral part of the retina cannot perceive as much detail. Its function is to make us aware of our environment and to alert us that there are objects that we should look at more closely. This is the function we use to orient us in our environment. It does not require eye movements and is used when we move through our environment.
- As the name suggests, macular degeneration affects only the macula. So it may affect your ability to read, write and watch TV.
- Dry AMD, the most prevalent form of AMD, does not involve any leakage of blood or serum. As dry AMD progresses, new blood vessels may begin to grow and cause wet AMD. These new blood vessels often leak blood and fluid under the macula. This causes rapid damage to the macula that can lead to significant loss of central vision in a short time.
- At this moment in time there is no proven cure for dry macular degeneration. Many treatments are under study and hold promise for the future, including nutritional therapies, electro-stimulation, and surgically relocating the macula.
“The most frequent cause of blindness”
You may see this statement associated with AMD, but it is important to understand that this statement refers to legal blindness, which refers to a government-designated degree of visual acuity loss (20/200 or worse). Because AMD affects only the macula but not the periphery, those with AMD do not go completely blind (but may qualify for “legal blindness” benefits).
AMD and your vision
Macular degeneration can affect your vision is a number of ways:
Visual Acuity loss
“Things aren’t sharp any more!”
The macula, which is affected in AMD, provides our sharpest vision, and when it is damaged, normal (20/20) visual acuity is no longer possible.
While the surrounding retina can still be used, it is not as sensitive as the macula.
Because those with AMD retain peripheral vision, you may have AMD and still have adequate orientation and mobility performance yet a good deal of trouble reading.
Note: The loss of macula does not necessarily develop evenly nor start in the very center. The result may be a central island of vision, surrounded by scotomatous areas. When this happens, you may find you recognize a letter while having trouble recognizing a word.
“Words look wavy and letters vary in size.”
When retinal layers are stretched and distorted, vision can become wavy and distorted, somewhat like a funhouse mirror, but not as funny.
“Things appear and then disappear.”
Macular Degeneration causes scotomas – small areas of vision loss or blind spots. Things disappear when you first see something that is falling on the peripheral retina and you instinctively direct your gaze at it, causing the object’s image to fall inside the blindspot. When reading, for example, parts of words can disappear when they fall inside a scotoma.
Those with macular degeneration often experience increased sensitivity to light. You may find yourself bothered by bright lights at home. Those who experience this sensitivity may compensate by wearing sunglasses.
When you exit a dark room into bright sunlight the chemicals in the rods and cones become bleached out. Normally the chemicals produced to react to light are quickly reproduced, but when the retina is damaged by macular degeneration it may not be able to rapidly produce new chemicals, and you may experience dark spots and decreased vision for a while.
Decreased color vision
Color vision is provided by the cones, which are most concentrated in the macula. So as the macula degenerates cones are affected and your perception of color decreases.
Loss of depth perception
Depth perception depends on two fully functioning eyes, so macular damage can affect depth perception. You may notice this particularly with tasks that depend on central vision such as threading a needle., a problem you can be overcome by moving the thread front-to-back rather than right-to-left.
I’m seeing things!
With severe vision loss your brain may occasionally be unable to interpret the visual data it is receiving, and this misinterpretation may result in hallucinations, seeing things that aren’t there. These may worry you (“Am I going crazy?”) and you may be hesitant to mention them to others, even your doctor. This is a quite common phenomenon called Charles Bonnet Syndrome. It can be disconcerting at first but is just your brain unable to perceive what you are looking at.
Peripheral vision sensitivity
I can’t recognize faces but can see a paper clip on the floor.
The peripheral retina is sensitive to motion and to small objects and relative motion. Because AMD damages the central retina, you may be able to pick up small objects in your side vision while losing them when you try to focus directly on them. This ability can confuse others, such as family members, who may take this to mean you can see better that you actually can.
When central vision is lost, it is possible to learn to use peripheral vision as a substitute for it. See Eccentric Viewing below.
If you have macular degeneration and are experiencing some of the vision challenges described here, working with a low vision therapist is the best way to come up with strategies for optimizing your vision.
Magnification and lighting
Those with macular degeneration usually see better if things are larger or closer, so most people with macular degeneration benefit from some type of magnification.
Good lighting can also make a big difference, especially for reading and writing. Helping yourself
Each person with low vision from AMD responds differently to the different kinds of magnification devices and lighting enhancement available, so its best to test these with a low vision specialist. Getting help
Because it is the central macula that is damaged with AMD, you can train yourself to place the image of what you are looking at on the peripheral retina by turning your gaze slightly away from focus of your attention. In reading, for example, you may have better recognition by looking at the front or end of a word. This is called eccentric viewing.
Glaucoma Diabetic retinopathy Retinitis pigmentosa Cataracts