Describe the uses of pupil

Variation in the size, shape or reaction usually indicates some form of disease, disorder or use of medication. The pupil is usually dilated by the use of a topical mydriatic drug in the eye. In other cases dilation can occur due to acute glaucoma, retinal pathologies, optic nerve damage, and third nerve palsy. The pupil appears constricted in iritis and CNS diseases. Physical and physiological factors such as light intensity, light adaptation, refractive status, emotional factors, and age also affect the size of the normal pupil. The size and reactivity of the pupil are a measure of parasympathetic and sympathetic tone. The pupil may be irregularlyshaped in cases of anterior synechiae (due to corneal perforation) and in posterior synechiae (iridocyclitis and glaucoma).