It may affect one or both eyes and may come on gradually or occur suddenly. External ophthalmoplegia is paralysis of the muscles on the outside of the eye that control movement of the eyeball.
Internal ophthalmoplegia makes the pupil and lens unable to move.
Ophthalmoplegia may occur temporarily with migraine or the neuromuscular disorder, myasthenia gravis. It can also be caused by pressure on nerves that supply the optic muscles, whether from an aneurysm, brain tumor, or brain infection, such as meningitis. Fatty tissues in the eye socket swell and press on the eyeball, which makes the eye bulge outward and eventually paralyzes the eye muscles. Internal ophthalmoplegia impairs vision because the pupil is unable to react to variations in the amount of light reaching the eye, and the lens is unable to focus at different distances. However, if only one eye is affected, temporary relief from the distress of double vision can be obtained by wearing a patch over the paralyzed eye.