Expert: Dana Krempels, Ph.D. - 5/15/2010

Question
When I'm in a dark room and a bright light is suddenly turned on I feel discomfort / pain in my eyes.   Do animals with compound eyes experience this as well and do they have any mechanism to adjust for increasing / decreasing light levels like we do?

Answer
Dear Kurt,

The phenomenon you describe is pretty much an artificial one:  light levels in nature rarely flare as dramatically as artificial lights (except when there's lightning, and that lasts for a split second).  The sensation of discomfort one feels upon coming into a brightly lit area after being in the dark (and having dark-adapted eyes) may be due to the massive depolarization of many photoreceptors at once, leading to an overstimulation of the optic nerve.  This ceases quite quickly, once the photoreceptor pigments are isomerized and the huge wave of stimulus is reduced.

Whether insects and other animals with compound eyes feel this pain is anyone's guess.  (There's disagreement in the scientific community about whether these animals actually feel what we perceive as "pain.")  They don't have eyelids to squint, nor can they physically alter the amount of light entering the ommatidia except by behavioral means (i.e., turning away from the light).  But they probably have not had an evolutionary selective force to make this necessary, since artificial light is a relatively recent phenomenon.  And I'm not sure it would be a very powerful selective force--if at all--anyway.

Not much of an answer, I'm afraid.  But I hope it helps.

Dana