Understanding the Visual
from Macular Degeneration
Macular Degeneration may cause a number of specific visual problems. Understanding these problems can better help patients cope. Thinking of macular degeneration as just "bad vision or partial blindness" fails to help patients understand their many problems and prevents doctors from dealing with each separate problem the way we do at our low vision centers.
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Decrease of Visual Acuity
The sharpness of my vision is decreasing! The macula is the center of our vision and when functioning properly provides our sharpest vision. In macular degeneration, this area is damaged and visual acuity of 20/20 is no longer possible. The surrounding retina can be used, but it is not as sensitive as the macula.
I see wavy words, and the letters vary in size. Damage to the retina may result in distortion and wavy vision due to the stretching and distortion to the retinal layers. Imagine you are projecting slides onto a screen when someone wrinkles the screen. The image would seem to be wavy like a funhouse mirror.
Now I see it, now I dont. Macular Degeneration patients develop small areas of vision loss or blindness. They may see an object when it falls on the peripheral retina. Then as your brain attempts to look straight at the object, the image falls inside the blindspot and it disappears. During reading, words project onto the retina. Parts of the words may fall inside the blindspots, suddenly disappearing.
Patients find they must look slightly away or turn their head to see better. This is called eccentric fixation, and it is a simple way to place the image on the peripheral retina, which is not damaged by the degeneration. In reading, looking at the front or end of a word may improve recognition. Family and friends may mistakenly think the patient is not looking at them.
When I come in out of the sun, I dont see well! Photostress is a term used to describe beaching out of the chemicals in the rods and cones. These chemicals are created to react to light and thus create vision. Outside in bright sun, the light exposure uses up the chemicals. Unfortunately, the damaged retina may be unable to rapidly produce new chemicals and their vision may seem to decrease or dark spots appear. This is the same process we all experience when someone takes a flash picture of us, and we see a dark afterimage for a short period. Unfortunately, in macular degeneration the spot or decrease in vision may last much longer.
Most bright lights seem to bother me! General light sensitivity may increase in patients with macular degeneration. Some patients are unable to tolerate bright lights in their home. Due to this photophobia, patients usually begin wearing sunglasses to help cope with the bright lights.
Better Vision at Night
I see much better at night! The majority of the rod cells are located in the peripheral retina and are thus unaffected by macular degeneration. Rod cells function in lower levels of light allowing the patient to have better vision.
I no longer see colors as well. The macula has the highest concentration of cones, the cells that provide color vision. Thus with the degeneration of the macula, it results in damage to the cone color cells. Patient still see color but color perception may become more and more impaired in advanced macular degeneration.
Peripheral Vision Sensitivity
I see a tiny speck paper on the floor, but I cant see to recognize faces. The peripheral retina is very sensitive to small objects and relative motion. With the central retina damaged, the patient may not be able to see faces straight ahead while seeing stars, lint on a shoulder or speck of paper on the floor, because they are picked up in the peripheral retina or side vision. If they try to look straight at the object, it may disappear just as words or other objects do. Family members often mistake this ability as an indication that the patient can see better than he or she claims.
I see things that I know are not there! Am I crazy? Visual hallucinations may occur in any patients with severe vision loss. Patients are often afraid to mention them for fear someone will think they are crazy. These are not psychotic hallucinations, but are related to the brain misinterpreting the distorted image. This condition is known as Charles Bonnet Syndrome and has been reported in the literature for over 200 years. It was first noted by Swiss naturalist Charles Bonnet on observation on his grandfather.
My depth perception seems impaired! Depth perception is a very fragile visual function. Any decrease in vision may disrupt ocular depth perception. Two full functioning eyes are required for ocular depth perception. Threading a needle and other skills that require depth perception may become difficult.
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