While many individuals complain of difficulty adjusting to bright light, scientists have had little success in identifying an abnormality in the retina that causes this symptom. A research team led by scientists at the Massachusetts Eye and Ear Infirmary has identified genetic defects in five unrelated individuals that interfere with the ability of cells in the eye to quickly adjust to changes in light intensity. Their work is described in the Jan. 1 issue of Nature.
Researchers from the three laboratories located at the Massachusetts Eye and Ear Infirmary – the Ocular Molecular Genetics Institute (Thaddeus Dryja, Koji Nishiguchi, and Stephanie Hagstrom), the Berman-Gund Laboratory for the Study of Retinal Degenerations (Eliot Berson and Michael Sandberg), and the Howe Laboratory (Vadim Arshavsky and Kirill Martemyanov) – and from the Department of Ophthalmology at the University of Groningen in the Netherlands (Aart Kooijman and Jan Willem Pott), recently discovered a biologic basis for slow adaptation to light in some individuals. The photoreceptor cells in the eyes of normal individuals quickly respond to light and also quickly recover after exposure to light. Theoretically, it is possible to have a defect in either the activation or the deactivation of the photoreceptor’s light response. In the past, many defects in the activation phase have been found, and these typically lead to marked abnormalities in vision. This is the first report of patients with a problem with the deactivation of photoreceptors.
“In 1991, in the Netherlands, some patients were identified with abnormal recovery from the influence of strong light flashes. For example, they reported difficulty in playing ball games because they could not see a moving ball. With sudden changes in luminance, like that caused by going from inside to outside on a sunny day, these patients are essentially blind for five to 10 seconds,” said Kooijman from the University of Groningen. While some patients with cataracts can have related symptoms, these individuals had no cataracts.
“We found that their symptoms are due to defects in proteins that normally function to deactivate photoreceptors after exposure to light. The disease was due to mutations in the gene encoding these proteins,” said Dryja from the Massachusetts Eye and Ear Infirmary and the David Glendenning Cogan Professor of Ophthalmology at Harvard Medical School.
There is no cure for this condition; however, dark glasses to reduce exposure to bright light appear to be helpful. Those who experience extreme difficulty in adjusting to changes in light should consult with their physician. While the authors believe that these gene defects are uncommon, their discovery may provide clues to the basis for the milder difficulties that many individual experience when trying to adapt to changes in light intensity.