Reasons for Small Pupils

The human eye is approximately the size of a ping-pong ball and is comprised of several components, including the pupil, which dilates and contracts to control the amount of light entering the eye. Normally, the pupil contracts in response to light and dilates in darker conditions to allow more light into the eye. Continual pupil constriction may indicate an underlying medical condition, such as Horner Syndrome, drug use or anterior uveitis. Pupils also become smaller with age.

Horner Syndrome

• Horner Syndrome is a rare condition characterized by damage to the sympathetic nerves in the eyes and face. The condition typically affects one side of the face or one eye. Symptoms include small pupil size in the affected eye, ptosis (upper eyelid drooping) and decreased perspiration on one side of the face. Horner Syndrome is caused by an underlying medical problem, such as a cyst on the spinal cord, a tear in the lining of the carotid artery, injury to the spinal cord, stroke, cluster/migraine headache or a tumor. Treatment varies in accordance with the underlying cause of the condition.

Drug Use

• Small pupils may indicate drug use. Medications such as benzodiazepines, opioids and barbiturates all cause pupil constriction. Opioids include prescription medications, such as morphine, and heroin, an illegal drug. Signs of opioid use include small pupils, weight loss, slow movements and mood swings. Benzodiazepines are commonly prescribed to alleviate anxiety. Barbiturates, also called tranquilizers or sedatives, are prescribed to induce sleep. Symptoms of barbiturate or benzodiazepine use include small pupils, sleepiness, slurred speech and confusion.

Anterior Uveitis

• Anterior uveitis affects the front of the eye. It may be caused by eye disease or a complication of other medical conditions, such as cancer, rubella, inflammatory disorders or rheumatoid arthritis. It may also be caused by trauma to the eye. Without treatment, the condition can cause irreparable damage and vision loss. According to the American Optometric Association, symptoms of anterior uveitis include pupil constriction, inflammation in the eye and soreness in the eye. Treatment lasts several days to several weeks and consists of anti-inflammatory medication and prescription eye drops to dilate the pupils.

Aging

• Many older people require additional light. This is largely due to the effect of the aging process on the eyes. The aging process can result in diminishing pupil size; this, in turn, results in less light reaching the retina of an aging person. According to The Eye Digest, the average 20-year-old's eye receives approximately 6 times more light than the average 80-year-old's.