Miosis is constriction of the pupil of the eye. This is a normal response to an increase in light but can also be associated with certain pathological conditions, microwave radiation exposure, and certain drugs, especially opiates. The opposite, mydriasis, is the dilation of the pupil. Physiology of the photomotor reflex Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image-forming and the more newly discovered photosensitive gang… (More on Miosis)