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Ophthalmoplegia, or eye paresis, disrupts the VOR stabilization reflex, leading to incorrect perception. Without stabilization, the eye moves only where the head moves, which impacts quality of life.
Treatment of ophthalmoplegia depends largely on the degree of paresis-the fewer the number of muscles that are involved and the greater the degree of residual activity in the affected muscles, the greater the likelihood of successful surgical treatment, said Steven M. Archer, MD.
Most ophthalmologists are familiar with standard muscle recess-resect surgery for limited forms of ophthalmoplegia. “Even when you have an isolated muscle that is completely paralyzed,
usually a lateral rectus muscle, there are some pretty good options” said Dr. Archer, professor of ophthalmology, University of Michigan Kellogg Eye Center, Ann Arbor, MI. “We have a variety of transposition techniques, moving adjacent working muscles, to provide the force the paralyzed muscle can’t provide.”
But when faced with more extensive ophthalmoplegia-an eye with very little movement or when neither eye moves-there can be perceptual problems, in addition to diplopia, that are not widely appreciated.
“Besides causing strabismus, ophthalmoplegia disrupts the vestibulo-ocular reflex (VOR) as well as the patient’s perception of visual direction,” Dr. Archer said. The VOR is the mechanism that enables the eyes to remain fixed on a specific object as the head moves. Without stabilization of the eye position by the VOR, the entire visual world seems to move whenever the head moves. Perceptual disturbances due to abnormalities of the VOR are well-described in the ear, nose, and throat literature as spatial disorientation and oscillopsia, Dr. Archer said.
Ophthalmologists are more familiar with oscillopsia associated with eye movement in acquired nystagmus, but they should also be aware that head movement can produce similar symptoms of visual movement and spatial disorientation in the absence of a normal VOR.
Another potential complication arises from the way in which the brain perceives visual direction after voluntary eye movements.
“For example, if you glance to the left, your perception is not that the object you were looking at straight ahead has jumped to the right, but rather it seems to remain in the same place,” Dr. Archer explained. “A stable visual world, in spite of falling on different retinal locations as you move your eyes, requires you to constantly adjust your perception of visual direction to account for where the eyes are pointed.”
Because the eye has essentially no proprioception, the brain must adjust its perception of visual direction through a feed-forward mechanism, also known as efference copy, he noted.
“The brain knows where the eyes are pointed because of the innervation it is sending to the eye muscles,” he said. “Your perception of visual direction will be incorrect if that innervation, in the presence of ophthalmoplegia, doesn’t put the eyes in the position that the brain expects.”
Array of symptoms
Many patients with ophthalmoplegia experience symptoms from the mismatch between visual perception and head or eye movement as a transient problem. Depending on the muscles involved and the severity of the paresis, the brain may be able to compensate. Younger patients may exhibit greater neural plasticity and adapt more readily than older patients. “But there are some patents who never adapt,” Dr. Archer said. “For these patients, ophthalmoplegia can be very disabling.”
Patients with complete ophthalmoplegia in which one or both eyes do not move, may have even greater problems. Even if with good vision, unless the unmoving eye is fixed straight ahead, patients cannot see well. A patient with vertical apraxia from a stroke or other injury might have the fixating eye looking sharply up or down. The only way to compensate is to tilt the head in the opposite direction. That can leave the patient with head tilted sharply forward or backward simply to point the eye approximately straight ahead.
Patients with a horizontal displacement have a similar problem. The fixating eye is pointed off to one side, which requires them to turn the head sharply in the opposite direction in order to see anything in front of them. “You end up with an awkward, uncomfortable head position that can be functionally and socially difficult,” Dr. Archer said. “It’s important to remember that muscle surgery to place the eyes in a more central location can be a big help to these patients.
“Even in cases where we are unable to surgically restore any range of eye movement, we may be able to move the eyes to restore a little binocular vision, improve the head posture needed to use those immobile eyes and improve their appearance, which can make a significant social and psychological difference,” he added.
Steven M. Archer, MD
This article was adapted from Dr. Archer’s presentation at the 2017 meeting of the American Academy of Ophthalmology. He did not indicate a proprietary interest.