ESSENTIAL blepharospasm is a focal disturbance of the central nervous system producing progressive involuntary, spasmodic closure of the eyes. As it progresses, the patient becomes visually crippled even though having normal visual pathways because the eyes are closed almost 25% of the time.
In a thorough monograph, Henderson1 postulates that the disorder is the result of a disturbance in the inhibitory apparatus between the pyramidal and extra pyramidal system, located in the suppressor strip 4-S of Hines or the bulbar reticular formation. Since cortical representation of the orbicularis oculi is bilateral and much greater than lower half facial muscles, a loss of 4-S fibers in this area has a greater effect on the eyes than other muscles of the face.1
Essential blepharospasm typically begins in the sixth decade of life as a "blinking" in one or both eyes and progresses to bilateral involvement and functional blindness. Most patients
Harvey HK. Resection of the Facial Nerve for Blepharospasm. Arch Ophthalmol. 1971;86(2):178-181. doi:10.1001/archopht.1971.01000010180010