Anisocoria is a condition where one pupil is larger than the other, caused by various disorders ranging from harmless to life-threatening. Adie’s pupil and Horner’s syndrome are two common causes, with Adie’s pupil usually benign and Horner’s syndrome often a symptom of a more serious problem. Other causes include damage to the iris sphincter, insufficiency of parasympathetic innervation, and oculomotor nerve palsy. About 20% of people have mild physiological anisocoria.
Anisocoria is a physical condition characterized by one pupil being larger than the other. A variety of disorders can cause this irregularity, including Adie’s pupil and Horner’s syndrome. It could also be caused by damage to the iris sphincter, insufficiency of the parasympathetic innervation, oculomotor nerve palsy, or other causes. The severity of these causes ranges from harmless to life threatening.
About 20% of people have mild physiological anisocoria. In most cases, pupil size can change randomly throughout the day. Patients who have additional symptoms in combination with irregular pupil size could have a more serious disorder.
Adie’s pupil is a condition that usually affects women between the ages of 20 and 40 and is caused by a viral infection in the nerve tissues of the eye. This condition is usually benign and does not cause serious bodily harm, and there is no specific treatment for it. Sometimes, patients might also suffer from an irregular heartbeat, low blood pressure when standing up, loss of reflexes, and areas of the skin that no longer produce sweat. This condition is called Adie syndrome and is treated by changing the patient’s diet and lifestyle.
Another condition that can make one pupil larger than the other is called Horner’s syndrome and is typically accompanied by a slightly droopy eyelid. This disorder is usually a symptom of a more serious problem rather than a disease itself. Some patients develop Horner’s syndrome due to a brain injury or stroke. Other possible causes include lung cancer, spinal cord damage, or carotid artery damage. Many of the disorders that cause this condition can be life-threatening.
In the case of Horner’s syndrome, one pupil appears larger than the other because the pupil of the affected eye is smaller. Both pupils react to bright light at equal rates. Some patients also stop sweating or sweat less on one side of the face than the other.
A patient might also have one pupil larger than the other if they suffer damage to the iris sphincter. The normally round iris develops an irregular shape and the eye may be swollen or inflamed. A doctor can examine the eye to look for damage to the muscles.
There are many other reasons for having pupils of different sizes, including parasympathetic innervation failure, which is a condition in which the pupil is no longer able to contract normally and remains dilated. A disorder such as third cranial nerve or oculomotor nerve palsy can cause this secondary condition. Migraine headaches, eye infections, exposure to atropine medications, and previous eye surgeries can also leave one pupil larger than the other.
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