Complex Visual Hallucinations and Macular Degeneration

Complex Visual Hallucinations and Macular Degeneration

Located in the center of the retina, the sensitive macula provides us with sight in the center of our field of vision. When we look directly at something, the macula allows us to see the fine details. This sharp, straight-ahead vision is necessary for driving, reading, recognizing faces, and doing close work, such as sewing. Macular degeneration is the impairment of this central macular area. Age-related macular degeneration (AMD) is the most common cause of vision loss in the Western world in the over 50 age group. It most commonly affects those of northern European descent and is uncommon in African-Americans and Hispanics. The prevalence increases with age. It affects about 15% of the population by age 55, and over 30% are affected by age 75 (Miller, 1992).

In macular degeneration a layer beneath the retina, called the retinal pigment epithelium (RPE), gradually wears out from its lifelong duties of disposing of retinal waste products. Eventually the capacity of the RPE layer to handle these metabolic products is overwhelmed and the RPE begins to degenerate (Miller, 1992). Other deep layers involved in development of macular degeneration are Bruch's membrane and the choroid layer. Additional factors that may hasten loss of the RPE layer, and the resulting degeneration of the central retina (macula) include hereditary factors, ultraviolet rays from sunlight, and blue iris color (more UV rays reach the retina in blue-eyed patients, probably because of the lower pigment density in the eye).

There are basically two forms of macular degeneration. So-called dry (or atrophic) macular degeneration, which accounts for 90% of cases, is caused by the aging and thinning of the tissues of the macula (Miller, 1992). This type is characterized by tiny yellowish deposits under the macular part of the retina. These deposits are known as drusen and may increase in size and number over time. Areas of loss of retinal and RPE layers in the macula may gradually appear. Small clumps of brown pigment from the degenerating RPE layer also are commonly seen.

The other major form of this disease is wet (or exudative macular degeneration) which is a much greater threat to vision loss even though it accounts for only 10% of cases. This type can be associated with a more sudden loss of vision due to leakage or bleeding under the macula from abnormal vessels, called the choriocapillaris, arising from one of the deeper layers.