Spotting eye disease sooner

Roxanne Stein

BACKGROUND: Macular degeneration is the age-related degenerative process of the macula. The macula is the area of the retina that is responsible for fine visual acuity. Macular degeneration can make it difficult or impossible to read and recognize faces and it's a major cause of blindness in the elderly. Age-related macular degeneration (AMD) begins with characteristic yellow deposits in the macula, called drusen. People with drusen can go on to develop advanced AMD. The risk is considerably higher when the drusen are large and numerous and associated with disturbance in the pigmented cell layer under the macula. Recent research suggests that large and soft drusen are related to elevated cholesterol deposits and may respond to cholesterol lowering agents.

There are two forms of AMD -- wet and dry. Central geographic atrophy, the dry form of AMD, results from atrophy to the retinal pigment epithelial layer below the retina, which can lead to blindness through loss of photoreceptors (rods and cones) in the central part of the eye. Neovascular or exudative AMD, the wet form of AMD, causes vision loss due to abnormal blood vessel growth in the choriocapillaries, ultimately leading to blood and protein leakage below the macula. Bleeding, leaking and scarring from these blood vessels can eventually cause irreversible damage to the photoreceptors and rapid vision loss if left untreated.

DIAGNOSING: The traditional way to diagnose macular degeneration has been with the Amsler Grid Test. The Amsler Grid is a pattern of intersecting lines, identical to a piece of graph paper, with a black dot in the center. A person with normal vision can fixate on the dot while still seeing the grid patterns. A person with macular degeneration will see part of the grid missing, or some of the grid lines will appear to be bent or unevenly spaced.

A new test called prospective hyperacuity perimetry, or PHP, is able to detect the change from dry to wet AMD. The computerized test is more accurate because it has a higher sensitivity level. It will detect a change from dry macular degeneration to the wet form faster or at an earlier stage than traditional testing. PHP testing works by showing a series of linear dots in a pattern and it tests the entire 14 degrees of the macular fields. It tests small portions at a time in a prearranged sequence. The patient is asked to detect if any of the dots arranged in a line are out of space. The PHP test also incorporates some dot sequences that really are out of order, allowing it to test a patient's reliability in answering. A computer records the data and can detect even the smallest changes in a patient's macula over time.