Macular degeneration is a disease that usually affects older people that can cause severe loss of central vision. The macula is located in the center of the retina--the light sensitive part of the eye that sends nerve signals to the brain. Age-related macular degeneration (AMD) always begins with the dry form of the disease which is much more common than the wet form. The dry form presents in three stages.
Early Stage of Dry AMD
The dry form of AMD usually affects both eyes, although one eye may appear to be unaffected. A common, early symptom is the appearance of drusen. These are yellow deposits under the retina that the doctor can detect during a dilated eye exam. The patient will not yet show symptoms of vision loss.
Intermediate Stage of Dry AMD
The patient will begin to experience blurriness in his central visual field. The drusen will appear as either one or more large-sized deposits or as many medium-sized deposits. This will make it difficult to identify faces, and close work such as reading or sewing will become difficult. However, improved lighting, reducing glare and color contrast will help the patient be able to perform these tasks.
Advanced Stage of Dry AMD
During this stage further breakdown of cells and tissue in the retina cause more severe loss of central vision. The blurred area gets bigger and larger so that the patient cannot read or recognize faces unless they are very close. Scientists are unclear about the relationship between drusen and AMD, although they know that the patient with more and larger drusen deposits has a greater risk of developing the advanced form of the disease.
Charles Bonnet Syndrome
As vision in the blurred area worsens to the point where there is no vision, it is called a "blind spot" or "scotoma." In some cases the person may experience hallucinations in the scotoma. This condition is called Charles Bonnet Syndrome--named after the Swiss naturalist who described it in 1769. It is important that patients with AMD learn about this possible disarming condition so that they will understand that it is not a symptom of mental illness.These recurrent hallucinations are typically of people or animals that are smaller than normal and they seem to fit into the person's surrounds. For example, if the person is watching television, she might see a monkey in the scotoma that looks like it is sitting on top of the television. Neurologist Oliver Sacks has extensively described these hallucinations in books and lectures.
References
- "Age-Related Macular Degeneration; What You Should Know"; National Eye Institute; 2003.
- "Foundations of Low Vision: Clinical and Functional Perspectives"; Anne L. Corn and Alan J. Koenig; 2004.
- "Low vision Rehabilitation"; Mitchell Scheiman; 2007.
