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Reading with a Central Retinal Scotoma (12/2010)
( lcburkhardt@brailleinstitute.org )

When held at a distance of approximately 16 inches from the eye (using eyeglasses for reading if necessary), this diagram (PDF at psy2.ucsd.edu) represents the central 30 degrees of a normal visual field. When a person without vision impairment looks straight at the dot in the center of the diagram, the size of the surrounding letters represent the smallest sizes of print that areas of retinal tissue can recognize. Retinal cone-cell density gradually decreases on areas that are farther away from the center of the retina. (Cone cells respond to daylight levels of illumination.) As cone-cell density decreases, images appear less distinct.

If a person loses cone-cells in the center of the retina, the size of the blank area (scotoma) in the best eye determines the smallest size of print that the person can see on this diagram. The larger the central scotoma, the larger the print needs to be for a person to recognize it.

Central retinal scotomas:

1. Cause a decrease in visual acuity that is not correctable (unlike focusing problems which are typically correctable with eyeglasses).
2. Disrupt the visual field. The area of sharpest vision is directly adjacent to a blind area. Even with training and practice to learn how to avoid the scotoma, more controlled eye-muscle movements are needed to locate and maintain fixation on the area of best acuity. This effort can cause visual fatigue to one degree or another. Viewed objects can easily disappear into non-seeing areas. Visual tasks that require tracking (like reading sequential words) are especially disrupted.

For these reasons, people with central retinal scotomas are encouraged to make the print large enough that they are able to read as comfortably as possible. Increasing contrast (making the print stand out from the background using black print on a white background or by using task lighting or electronic magnification systems) and using bold, uncluttered, well-spaced print can also improve reading ability. Then, people are additionally encouraged to read for as long as they are able without causing excessive fatigue, eye-strain or headaches. Reading in the morning when your eyes are rested, or taking breaks to rest your eyes can sometimes extend time spent reading during a day. Typically, the larger the print needs to be for a person to read, the slower the person will read, and the sooner they will need to stop reading due to visual fatigue.

If visual reading tasks cause excessive fatigue, people are encouraged to also explore audio options (such as audio books, computer text-to-speech systems and personal assistance) so that they can listen to some or all reading tasks depending on the severity of their reading stamina problems.

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