Blepharospasm is a common term for conditions that are medically known as Benign Essential Blepharospasm and Essential Blepharospasm. A blepharospasm is defined as "a chronic, unremitting, bilateral, variably progressive dysfunction of the nerve that controls the muscles around the eye." It manifests itself as an uncontrollable, forcible closure of the eyelids. It often affects both eyes at once, but it can also affect only one eye. In some cases, other muscles in the face can twitch as well, especially around the cheek and brow. Severe blepharospasm can cause the eyelids to be forcibly closed for a duration longer than the typical blink reflex, causing a variable interruption in the ability to see. Benign Essential Blepharospasm and Essential Blepharospasm are caused by abnormal nerve impulses to the eyelid muscles. Years ago, many patients were told that Essential Blepharospasm was caused by psychiatric problems. Now, it is known that this was not true.