Ocular Myasthenia Gravis
By A Representative of The Myasthenia Gravis Association of Western PA
Over two-thirds of all patients with myasthenia gravis (MG) begin with symptoms relating to their vision. Overall, the ratio of affected females to males in generalized myasthenia is 3:2 or higher. In ocular myasthenia, men are more frequently affected, especially after the age of 40. In addition, the average age of onset for generalized myasthenia is 33 years, while that of ocular MG is 38 years. The ocular motor system may be especially vulnerable to myasthenia since it cannot adapt rapidly to variable weakness. The most common symptoms seen in patients with ocular myasthenia gravis are diplopia (double vision), ptosis (drooping eyelids), and incomplete eye closure. Compared to other involved skeletal muscles, only slight weakness of the extraocular muscle may cause diplopia and visual disturbances to occur. These symptoms occur due to weakness of the muscles that control eyeball and eyelid movement. Light sensitivity due to sluggish pupils may occur in some patients. Symptoms are frequently influenced by environmental, emotional, and physical factors. Some of these factors include bright sunlight, extremes in temperature, emotional stress, illness, surgery, menstruation, and pregnancy, among others. Symptoms tend to be worse at the end of the day. Increase in muscle weakness after repetitive or sustained effort and improvement following rest are important features of this disease.
Symptoms
Diplopia (di-plo-pe-a), or double vision results when the eyes cannot be focused as desired due to weakness of one or more of the extraocular muscles which control eye movement. This most often occurs when looking up or to the side. To compensate for the weakness, the patient may tilt his/her head or turn their face to allow the stronger eye muscles to work. For example, if the muscle which allows the eye to look upward is weak, the patient could tilt their head back to look up.
Ptosis (to-sis) is the drooping of one or both eyelids, also due to muscle weakness. Fluttering or twitching of the drooping eyelid may occasionally be seen. If both eyelids droop, it is common for one to drop more than the other.
Nystagmus (ni-stag-mes), or constant involuntary repeated movements of the eyeball in any direction may also occur in one or both eyes.
Diagnosis
The edrophonium (Tensilon) test has remained the first-line test for diagnosis of MG. The Tensilon test consists of injecting a small amount of the medication edrophonium intravenously. If the patient has MG the ocular muscle weakness, the ptosis, the general muscle weakness and/or nystagmus will improve dramatically for a short period of time. Usually, a blood test called acetylcholine receptor antibody titer (AChR Ab) is taken as well. Additional laboratory studies may include other antibody studies and a sedimentation rate.
A test to check for fatigue and weakness of the eye muscles which may be done by the examining doctor includes attempting to open the eyes while the patient tries to hold them closed, sometimes called a “peek sign.” This may result in one or both eyes opening, and the patient appears to “peek” at the examiner.
The “sleep test,” which is based on the tendency for MG symptoms to improve follwing rest, may be especially useful in cases where a Tensilon test is technically difficult. This may be used in small children, patients with poor veins, or allergy or sensitivity to anticholinesterase drugs such as Tensilon. There are many ways to conduct this test, but in most the patient is photographed and ocular motility (eye movement) is measured. The patient is then placed in a quiet, darkened room and instructed to close his/her eyes for 30 minutes. After this, the photographs and ocular motility tests are repeated. The test is considered positive if there is improvement in the ptosis and/or ocular motility following the rest.
The morning/evening comparison test is similar in concept to the sleep test. The patient is photographed, and the ptosis and ocular motility are compared at different times during the day. Old photographs are very helpful to determine how long the patient has drooping the of the upper eyelids.
The “ice” test is a simple test for ocular MG in patients who have ptosis. A surgical glove filled with ice is held against the droopy eyelid for several minutes. In ocular myasthenia the patient can open his/her eyelid normally for a short period of time after the ice is removed.
Another simple test for ptosis is the “fatigue” test. This consists of having the patient look at an object held up by the examiner in front of the patient. After a short period of time the eyelid(s) will droop in the person with ocular MG.
An MRI or CT scan of the head is often done to rule out other possible causes of the patient’s symptoms. Additional testing may also be required to confirm the diagnosis.
Treatment
Both ocular and general myasthenia gravis patients tend to have remissions and exacerbations at irregular intervals, so that the medications that are used for treatment may need to be changed accordingly. Medications may include cholinesterase inhibitors such as pyridostigmine (Mestinon), steroids such as prednisone, or other immunosuppressants used alone or in combination. Neostigmine (Prostigmin) or ambenonium (Mytelase) may be used for patients who cannot tolerate Mestinon. Cyclosporin (Sandimmune) may be useful in patients who cannot tolerate prednisone. Azathioprine (Imuran) has a significant immunosuppressive effect, although its exact mechanism of action is not well understood.
In addition to medications, other options which may be used are plasmapheresis or intravenous immune globulin (IVIG) therapy. These treatments offer only a temporary improvement and repeated treatments are necessary to sustain the effect. While thymectomy (removal of the thymus gland) is often recommended for patients with generalized MG, it is rarely used in purely ocular MG unless a thymoma is suspected.
In those persons whose ocular myasthenia is not adequately controlled by medicine, several aids are available. In many patients, simply wearing a patch over one eye will eliminate the double vision. The patients may alternate the eye patch from one to the other to avoid eye strain. Another method is wearing one contact lens which is opaque (can’t be seen through). This may also be changed periodically from one eye to the other. Ask the ophthalmologist how often this should be done. Special prism glasses may also help to correct double vision in some cases.
When both eyelids droop, taping one eyelid open may improve vision. The use of non-allergenic tape such as paper tape is suggested. Once again, eyelids may be alternated to prevent eye strain. Another way to hold one or both eyelids open is to have ptosis bars or eyelid crutches attached to the eyeglasses. These are thin, flexible wires which attach at the bridge of the nose and may be free-floating at the other end or attached to the frames near the hinges. The wires rest against the eye socket and hold the eyelid open like a brace or crutch. These devices must be carefully fitted and adjusted by an ophthalmologist. Most patients report that the eyes adjust to the bars after a time, and they are much more convenient than taping the lids open. Since the yes can’t blink normally, dryness and irritation may result. It is important to remove the glasses frequently to allow the eyes to close so the eye can be moistened. Some MG patients have advised that ever ten minutes or so is a good guideline. Artificial tear drops and forced blinking may also help. If the patient has double vision in addition to drooping eyelids, one eye should be allowed to close and the other be held up by the ptosis bar. Eyelids can easily be alternated when the glasses are removed to allow eyelids to close and moisten the eye. It is important to remember not to fold these eyeglasses, or carry them in a pocket or a purse as the bars bend easily and adjustment could be misaligned or altered. Where ptosis does not respond to medications of conservative treatment, surgery may be suggested to lift the eyelid or lids. Because this is a permanent and irreversible method of opening the eye, it is only done in very rare cases.
Weakness of the muscles that control eye closure (the orbicularis oculi) may result in the patient getting soap in their eyes when bathing, and in excessive tearing due to incomplete blinking. The use of non-irritating shampoo, such as baby shampoo, may be of help. Swimming goggles may also be worn when bathing or swimming to prevent eye irritation. The neurologist or local MG organization may be able to recommend the eye care specialist who is experienced in treating patients with MG. When calling to make an appointment with the ophthalmologist, ask about their experience with treating MG patients, possible costs, and insurance coverage. A call to the patient’s insurance carrier to verify the ophthalmologist participates in their plan and to ask about coverage for special glasses would also be a good idea. When meeting with the ophthalmologist, it is important to ask questions about how to prevent eye strain, maintaining moisture in the eyes, and how often to alternate the taping or bracing of eyelids, if applicable.
Additional tips which may help with vision problems include closing the eyes for
30 minutes before going out, to allow the eyes to rest and regain strength. An
eye patch may be carried in a pocket or purse to slip on if double vision
develops.
In summary, the clinical observations which distinguish ocular myasthenia from generalized MG include: highly restricted ocular symptoms such as diplopia, ptosis, and weak eye closure. The good news for patients with ocular MG is that if they continue to have only ocular symptoms for three years, there is a very good chance their symptoms will not increase. The use of the above strategies can make it easier to live with ocular MG.
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