Vision care for people with diabetes is critical because disturbances of normal sight are common. Until recently it was thought that vision changes were the result of damaging changes in the structure of the eye.

However, researchers have now discovered that subtle changes of vision actually precede observable eye changes and, furthermore, are directly related to momentary fluctuations in blood glucose levels.

What's significant about this finding? It has been estimated that 70% of young type I patients without retinopathy have color vision changes. The discovery that these early vision changes are related to diabetic meta- bolism raises hope that eye complications may be avoided or corrected and managed before any structural change, which is often irreversible, occurs in the eye.

Dr. Marilyn Schneck and her colleagues at the University of California Berkeley School of Optometry, working with Dr. John Linfoot of the Diabetes and Endocrinology Institute in Oakland and Dr. Everett Ai at the California Pacific Medical Center Ophthalmology Department in San Francisco, have shown that the fluctuations in blood glucose can be associated with rapid, systematic, and very selective changes in vision and are specific to one of the three kinds of cone receptors (light-catching cells) in the eye.

These receptors, the blue light-catching cones, are specialized for color vision. As blood glucose rises, the changes in vision are heightened; conversely, lowering blood glucose toward euglycemia improves vision.

It is known that some people with diabetes experience noticeable color vision changes. There have even been reports of more vivid color vision during hypoglycemic episodes (also experienced by non-diabetic athletes after over-exertion).

However, this new research measures vision changes caused by increases, not decreases, in blood glucose levels, where subjective color vision changes may be more subtle. Such changes have practical disadvantages, whether perceived or not. For example, the subtle changes due to fluctuating blood glucose may make the reading of color-coded test strips even less reliable.

The researchers have found that these subtle vision changes are detectable by recording tiny brainwave responses to lights that stimulate the blue cones. Researchers measure these signals while the patient looks at colored stripes on a computer screen. When patients' blood glucose levels rise, the brain signals become slower and smaller. (Other tests show that blue spots of light must be brighter to be seen by patients when their blood glucose levels are high.)

There are at least two types of color vision changes that people with diabetes experience-temporary and permanent. One possible result of this research is a determination of whether or not the color vision changes accompanying momentary blood glucose fluctuations are present only in people who have not yet developed secondary eye complications. Researchers also hope to determine whether or not vision changes are a sign that secondary eye complications are imminent.

How high are your blood glucose levels before color vision changes? What vision changes indicate damaging blood glucose levels? If blood glucose levels are high enough to affect your short term vision, is this a sign that you will begin to develop complications of retinopathy? These are some of the questions that this new research may eventually answer.

While the researchers don't anticipate that these studies will lead to a non-invasive blood glucose test, they hope that color vision monitoring may eventually act as a predictor of retinopathy.

Individuals who are interested in or who wish to participate in this research should contact Dr. Marilyn Schneck at the University of California at (510) 642-5904.