Discovery of a Third Photoreceptor System in the Eye

Light affects many types of non-visual biological processes including our internal circadian clock which controls daily sleep cycles.  Many of the body’s non-visual responses to light are in some part controlled by a recently discovered third type of photoreceptor in the eye discovered by Ignacio Provencio.

The two main classes of photoreceptors are rods and cones. The third class that has been discovered is a photoreceptor ganglion cell containing a photopigment called melanopsin. The body needs rods, cones, and melanopsin in order to be able to constrict the pupil in response to light as well as to develop and maintain a circadian rhythm. Without melanopsin, the rods and cones would be able to compensate for only some of the missing receptors but they cannot fully compensate.

The importance of melanopsin falls primarily in the study of people with visual blindness or visual impairments. Depending on the type of disease or disorder that has caused blindness, the eye may still contain some of the photoreceptor ganglion cells containing melanopsin. This means that despite having no visual response to light, a person could still be capable of physiologically responding to light through the eye. In many cases of blindness, it is important for the eye to be exposed to several hours of light during the day because the eye plays such a prominent role in maintaining the internal circadian rhythm. However it is important to note that each eye disease is different, and in some instances light could make it worse. There are different types of treatments to help with sleep cycles for people with certain types of eye diseases that may not allow them to expose the eye to light.

Light affects the body in many other ways as well, including the production of the hormone melatonin and even the regulation of heart rate. It is crucial to understand the effects of light on the body for all types of interior environments.

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