Two types of photoreceptors react to light falling on the retina. Rod cells (green) are usually located around the edge of the retina and function in peripheral vision. Cone cells (red) are concentrated more centrally, and are responsible for high-resolution color vision.FLICKR, NATIONAL EYE INSTITUTEOn August 21, the moon will pass between the Earth and the sun, resulting in a total solar eclipse visible across a large strip of the United States. Self-proclaimed eclipse-chaser Ralph Chou, an emeritus professor of optometry at the University of Waterloo, has been working to spread awareness about eye-safety during eclipses for around 30 years. Last year, he put together the American Astronomical Society’s technical guide to eye safety, aimed at everyone from astronomers to educators to medical professionals.
The Scientist spoke to Chou to find out what happens to the eye when exposed to too much sunlight, and how to watch next week’s solar eclipse safely.
The Scientist: How can too much sunlight damage the eye?
Ralph Chou: Light comes into the eye and goes through all the various layers of cells until it reaches the photoreceptors—essentially, the bottom of a stack of cells. The photoreceptors themselves guide the light towards a specialized structure [of the cells] called the outer segment, where there is a stack of discs that contain the visual pigment. Under normal circumstances, the light would interact with the pigment, which generates an electrical signal that then starts the process of sending an impulse through the optic nerve to the ...
