< < Story continued from previous screen

Lazy Eyes:
'Don't Make Two Problems If You Only Have One'

Most neuromuscular conditions affect muscles that are considered voluntary -- that is, those that can be moved at will. Such muscles share a similar structure and function and look similar under the microscope. But not all voluntary muscles are exactly the same.

Six extraocular muscles -- four straight and two diagonal -- surround each eyeball and allow it to move in all directions. Weakness in any of these can lead to an inability to move the eyes or, if the two eyes are differently affected, to strabismus.

The extraocular muscles, six small muscles that move the eyeball in all directions, are voluntary muscles, but they have characteristics that make them slightly different from other such muscles. That may explain why they're particularly hard hit in some neuromuscular conditions, such as the myasthenias, mitochondrial disorders, myotubular myopathy, OPMD, myotonic dystrophy and thyroid-related muscle disorders. It also may indicate why they're almost never involved in Duchenne or Becker muscular dystrophy, limb-girdle muscular dystrophies, the merosin-deficient form of congenital muscular dystrophy, or the motor neuron disorders spinal muscular atrophy and amyotrophic lateral sclerosis.

There are six extraocular (EO) muscles for each eye -- four straight, or rectus, muscles; and two slanted, or oblique, ones. Normally, the EO muscles work together with each other and with the muscles of the other eye to allow the gaze to be focused in any direction and to ensure that both eyes are sending the same image to the brain.

When one or more of the EO muscles weakens, the eyeball can't be moved in the direction in which that muscle would normally move it, such as upward (superiorly), downward (inferiorly), inward toward the nose (medially), or outward toward the ear (laterally).

If EO muscles in both eyes weaken at about the same rate and in the same way, there isn't much to worry about, says Andrew Lee, a neuro-ophthalmologist -- eye doctor who specializes in eye-brain interactions -- at the University of Iowa Hospitals and Clinics in Iowa City.

Fortunately, says Lee, that's usually the case in neuromuscular disorders. EO muscles may weaken, but they tend to weaken equally in both eyes. Such patients don't need to have eye muscle surgery, he says, because, although the eyes are unable to move, they're equally unable to move.

People with this condition "just turn their heads to see," Lee says. "They just pick their heads up or turn the head from side to side to see in different directions. If it's been like that for a long time, they just get used to it. Many patients don't even know that their eyes don't move."

The eye receives light through the pupil, a hole in the colored part of the eye, the iris. The cornea, which covers the pupil like the glass over a watch face, helps focus the light, as does the lens, just in back of the pupil. Drying and damage to the cornea can result when the eye doesn't close properly. A cataract can occur in myotonic dystrophy or with prolonged use of corticosteroids. Abnormalities in the retina, the "screen" onto which images are projected, occur in some mitochondrial disorders.

Trouble comes when EO muscles in the two eyes don't weaken the same way or at the same rate. That causes a condition known as strabismus, meaning eyes that can't focus on the same object at the same time.

People with strabismus see one image with one eye and get a slightly different view with the other eye, sending two images to the brain. The result is double vision (sometimes of the same object, sometimes of different objects, depending on the type of weakness).

After childhood, double vision is a nuisance but not an emergency, because double vision that begins in adolescence or adulthood isn't likely to damage the visual process itself. In childhood, however, the situation requires immediate attention.

A simple treatment for double vision that starts after childhood is to block the vision from one eye, which can be done by wearing a patch or, more elegantly, a lens that looks transparent from the outside but blocks vision from the inside (called a Min lens, for its inventor).

In some cases, prism lenses can help align the eyes. These can be ground into the eyeglass lenses, if the problem is stable, or applied to the glasses as a thin, sticky sheet, if the problem is thought to be temporary or fluctuating. (These last are known as Fresnel prisms, after a company that distributes them.)

A new treatment for some kinds of strabismus is botulinum toxin, a bacterial poison that weakens muscles. It can be injected into a muscle that's too strong (pulling too tightly) to temporarily weaken it and thus straighten the eyeball. It's not a permanent solution, but it's useful in certain circumstances, particularly if surgery can't be done. As in ptosis treatment, EO muscle weakness in myasthenias and thyroid-related myopathies can often be corrected by treating the underlying disease with medication.

If medications aren't effective and the eye muscles aren't expected to change much over the years, surgery to correct strabismus can be undertaken.

Tired of Band-Aids, Counselor Plans Eyelid Surgery Linda Stullenbarger wasn't bewildered by what was happening when her eyelids began to droop about four years ago. "Oculopharyngeal muscular dystrophy is very prevalent in my family," says the 58-year-old counselor from Wheeling, W.Va. "The person who brought it into the family was my maternal great-grandmother, as far as I know. She had brothers with it, and out of her nine children, I think seven of them have been shown to have had it. "Back then, nobody knew what was wrong, but my mother had wonderful old pictures, and I noticed lots of droopy eyelids," Stullenbarger says. "I can remember my grandfather sitting with a sort of cap on, with it placed down over his eyelids and pulled up in such a way that it would open his eyes. I have a picture of him." For Stullenbarger, droopy eyelids aren't just an inconvenience or a cosmetic problem; they're also a professional handicap. "I'm an adolescent specialist. When somebody new comes in, I have to explain it to them. I've been asked, 'Are you going to sleep? Are you tired? Maybe I should go?' "I just tell them, 'I have a late-onset type of muscular dystrophy, and one of the things with it is that my eyelids droop, so I want you to know that you're not boring me or making me sleepy or tired.' "It's hard to explain, though. When you're working with people, you really use your eyes and your expression with them. You want to use your voice, your body, your eyes. You're attending to these people, trying to be with them, with what they're trying to say. I don't know how my facial expressions come across to them." Stullenbarger says she's heard some "nightmare stories" from family members who were unhappy with their ptosis surgery, and she wants to be sure she gets the right kind of surgeon to do hers. But she doesn't want to put it off much longer. A recent experience made her laugh, but also brought the problem home to her. "I started on a trip to see my brother and sister, who live about four hours from here. I was driving after dark, and I couldn't see. I stopped and looked around in my purse and found two Garfield [the cartoon cat] Band-Aids, which I used to tape up my eyes. "Then I had to stop on the way to go to the bathroom, so I stopped at a McDonald's with these Garfield Band-Aids on my eyelids. I had nothing else, and I had half a trip to go. I had to see. But people were just kind of going 'Um-hm.'" Becoming more serious, Stullen-barger says she now knows what her mother must have gone through. "When my beautiful mother, a very lovely woman, got older, her eyelids were so bad that she started wearing sunglasses, even to church. I asked her why, and she said it was because she looked so ugly. I said she could never look ugly, but now I understand what she meant. "You do feel kind of different. My husband and my doctor are the only people who see me without makeup now, and I want to go through our church directory with a hole puncher and punch out all my photos. I used to have very bright, wide open eyes. The droopy lids change the whole appearance of my face."

In children, strabismus is more serious, requiring immediate action. The reason for the urgency is that the child's brain is still developing, with connections between the eyes and the brain still forming up to about age 8 to 10.

When the brain receives two separate images, an uncomfortable situation for it, it simply shuts off the image from one eye. If that condition persists for a while, sometimes just a few weeks in young children, vision in the "rejected" eye is likely to be damaged. The resulting condition is known as amblyopia which literally means "dull eye" but is more often called "lazy eye."

Lazy eye isn't really eye damage, but a form of brain damage, in that the developing brain stops processing images from the eye it's decided to ignore and ultimately loses the ability to do so. Eye-brain connections in adolescents or adults are stable enough so that strabismus doesn't cause amblyopia. By the same token, however, amblyopia that starts in childhood isn't likely to be correctable with interventions after childhood.

Lazy eye is probably most often associated with strabismus, but it can also result from ptosis or from anything that interferes with the visual signals the brain normally receives from each eye during childhood. Keeping an eye covered can also cause amblyopia, which is why care has to be taken with therapies that involve patching of children's eyes.

"With children," cautions Lee, "it's urgent to prevent lazy eye if they have a droopy eyelid or a crossed eye. Don't make two problems if you only have one. If you wait until the child is older to correct the problem, you might have a lazy eye on top of, for example, congenital myasthenia. All these children should be examined and treated when they're young."

The treatment may ultimately be surgical, if the strabismus or ptosis is considered stable, but other therapies can also be used, in addition to or instead of surgery.

Most children with strabismus or ptosis in one eye will undergo treatment to patch or in some other way block the vision in one eye (for example, with Min lenses), forcing the brain to process signals from the eye it's been ignoring. To avoid amblyopia in the blocked eye, a careful schedule for the patching or blocking has to be followed.

Other Vision Problems:
Not Common, Sometimes Treatable

Neuromuscular disorders are more likely to affect the muscles that move the eye than they are the structures of the eye itself, but there are exceptions.

In myotonic dystrophy, a disorder that affects many organs, cataracts are found in nearly everyone. These are cloudy or scratchy spots on the eye's lens that can, as they increase in severity, interfere with vision. Fortunately, they can almost always be safely removed or dissolved and an artificial lens inserted.

Precautions with respect to anesthesia are important when anyone with a neuromuscular disease, particularly myotonic dystrophy, has surgery. The neurologist and the surgical team must consult before any procedure is undertaken.

Cataracts can also occur as a side effect of prolonged treatment with corticosteroids, the prednisone family of drugs. These are often used in inflammatory myopathies, autoimmune MG and Duchenne MD.

The eye's retina isn't often a target of neuromuscular disease, but it can be in mitochondrial disorders. Web sites and print materials unfortunately sometimes describe the problem as retinitis pigmentosa, which, if the reader looks it up, describes a group of genetic eye diseases, several of which can lead to blindness with time.

A better term is pigmentary degeneration of the retina, says Robert Daroff, a neuro-ophthalmologist at University Hospitals of Cleveland, and the problem usually doesn't lead to blindness, although it can lead to poor vision. Some mitochondrial disorders, such as Leigh's syndrome, can affect the optic nerves, "cables" that carry information from the eyes to the brain. This, too, can interfere with vision.

Neither Daroff nor David Chad has seen many neuromuscular patients with vision-threatening problems in their many years of practice. Daroff notes that vision problems in neuromuscular disease in general tend to be minor and pose less of a threat to one's quality of life than do other issues in these disorders. "I don't think patients should be overly sensitized about this," he says. "But if they have trouble seeing, they should see an eye doctor."

Parents, he says, should be on the lookout for crossed eyes or droopy lids in their children, and for the child who continually bumps into things or holds his head in an odd position and resists having it straightened. "Amblyopia," he says, "is absolutely avoidable."