How MD affects vision
Macular Degeneration is associated with a number of changes in vision. These are described in the literature by Richard Windsor O.D., F.A.A.O. and Laura K. Windsor, O.D. from the Low Vision Centres of Indiana (US). This article entitled "The Many Visual Problems of Macular Degeneration" outlines the following affects on vision:
Decrease in Visual Acuity
There are many different ways in which Macular Degeneration can affect a person's vision. A common symptom with MD is a decrease in visual acuity. People with MD can notice they are not reading as well. The vision is hazy or grey in the centre. The vision test may be failed when going for a driver's licence renewal and the person often needs to use the less sensitive side vision.
Good Days and Bad Days
Many people with MD report "good days and bad days". This is quite common with many ocular diseases. Lighting conditions, general health fluctuations and/or fluid changes in the retina are all common causes of daily variations in vision.
Distortion or Waviness in Vision
Another common symptom is visual distortion or waviness. As the macula region scars or leaks, it causes a stretching or distortion of the retina, leading to distortion in the image that can be seen. Window blinds or light poles may seem bent or crooked due to the damage in the retina.
Many people report that words "come and go" or "now I see it, now I don't". When the central vision starts to deteriorate because of MD, the person will experience a blindspot in the centre of vision. When looking off to the side using the peripheral retina they see the item, but when looking directly at the item, it seems to disappear. This often causes great frustration.
Phantom Vision or Charles Bonnet Syndrome (CBS)
Charles Bonnet Syndrome is a term used to describe phantom images or visual hallucinations experienced by some people with vision impairment. The images can take many different forms from patterns or lines, to people or buildings. Quite simply this is your eyes playing tricks. Charles Bonnet, a Swiss Naturalist, first noticed this condition in his grandfather. A person with severe visual impairment will see a distorted image, when they look at an object, because of the damage to the retina. This distorted image is transferred to the brain where the brain attempts to decipher the image. The brain ends up recalling an image from memory and making it quite vivid, as in a dream. This is simply the brain misinterpreting the visual image and not a psychiatric condition.
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Use of Eccentric Fixation
People with MD may turn their head or eyes to one side or the other in order to see more clearly. What they are doing is moving the macular scar out of the way and using their good peripheral vision for viewing. This turning of the eyes or head is called eccentric fixation and is often confused with the remaining peripheral vision.
The Paradox of Peripheral Vision Sensitivity
I see a tiny speck of paper on the floor, but I can’t see to recognise faces.
The peripheral retina is very sensitive to dim objects and relative motion. When the central retina is damaged, the patient may not be able to see faces straight ahead but may see stars in the sky or a speck of paper on the floor. This is because the objects are picked up in the peripheral retina or side vision. However, if trying to look straight at the object, it may disappear. Family members often mistake this ability to see small objects, as an indication that the patient can see more than he or she claims. This ability is termed the peripheral paradox of MD and is often confused with the more useful role of eccentric fixation.
Light Sensitivity and Photostress
Other major visual problems from MD are light sensitivity and photostress. Many people with MD are extremely bothered by bright lights both inside and outside. The scars in the eyes act as a mirror reflecting light internally within the eye. This causes light sensitivity and glare as well as haziness in the vision. Additionally, people with MD may notice that the vision drops when coming inside from bright sunlight. In this situation the damaged retinal cells cannot regenerate the retinal chemicals quickly enough. This is similar to the black spot seen in front of eyes for a few seconds after having a picture taken with a bright flash. With Macular Degeneration the spot or decrease in vision may last much longer.
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 relatively unaffected by Macular Degeneration. Rod cells function in lower levels of light allowing the patient to have better vision at night.
Decrease in Colour Vision & Depth Perception
The cone cells in the macula region are responsible for the majority of our colour vision. People with MD therefore report a muting or dullness in colours. Increasing light may aid colour vision. Additionally, a person with MD may have difficulty with depth perception and have problems judging steps. Whenever a person loses vision, depth perception is one of the first things to decrease. This is because it is a very sensitive function that requires two perfectly working eyes.
Our thanks to Dr Richard Windsor, O.D., F.A.A.O. for permitting the use of his article.