by Dan Roberts
Reviewed by Jennifer Galbraith, O.D.
Eccentric viewing is a technique used by people with central vision loss. Also called Preferred Retinal Loci (PRL), it is a method by which the person looks slightly away from the subject in order to view it peripherally with another area of the visual field. This is similar to looking slightly away from an object at night in order to see it better. By doing so, the viewer is allowing the rod cells in the peripheral field to take over for the cone cells in the central field. Rod cells are better for viewing in dim light than are cone cells.
In normal light, images are focused directly onto the macula, or the very center of the retina, where the cone cells are most dense. The cone cells are responsible for both color and fine detail vision. When they degenerate as a result of macular degeneration or similar diseases, the rod cells can be taught to take over to some extent. With proper training, concentrated practice, and proper adaptations, these less acute areas can act as a reasonable substitute. (Evidence of the brain’s ability to adapt to vision loss in this way was presented in the article, “Reorganization of Visual Processing in Macular Degeneration,” published in the January 19, 2005 issue of The Journal of Neuroscience.)
The biological task of eccentric viewing is complex. It requires the eyes and the brain to learn a new method of seeing, which means developing new habits and skills. This can usually be accomplished over a period of about six visits with a trained low vision therapist. In addition, home practice is important for supplementing the training and speeding the progress. It is difficult to self-teach eccentric viewing, because it can be frustrating, and an experienced, observant professional can help alleviate frustration by offering new approaches when others may not be working.
It is important to remember that training in eccentric viewing will not improve the condition of the retina. The patient may feel that vision has improved as a result, but that is simply because existing vision has been maximized.
The first step in the training is identifying the blind areas (scotomas). After that, techniques are introduced which help the patient learn to work around those areas. These techniques include tracing, identifying cards, and other methods used to improve reading and writing skills. Detail vision will not be fully regained by eccentric viewing training, but vision can be greatly improved when coupled with enlargement, enhanced contrast, and appropriate magnification devices. The level of reading ability that can be attained is determined in large part by each individual’s visual condition and determination.
For training in eccentric viewing, contact a low vision rehabilitation center. These can be located by looking in the phone book under “Rehabilitation Services,” by asking a low vision specialist, or by contacting the appropriate state agency for the blind, listed in the Resources section of this site.
by Dan Roberts