By Dr. Rabia Malik and Dr. Thomas Mizen
How Common is Ocular Myasthenia Gravis (MG)?
Symptoms related to eye weakness, or ocular symptoms, are common in patients with MG. Fifty percent (50%) of patients will present with ocular symptoms such as double vision and eyelid droop as their first symptom of MG. Over time, ocular symptoms can manifest in 70% to 90% of patients. In some cases, the initial presentation is with eye symptoms, and then the disease may generalize and produce other neuromuscular symptoms such as weakness of speech, swallowing or limb muscles. If the ocular symptoms persist in isolation without other neuromuscular symptoms for the first two years, then further generalization of MG is uncommon, and the diagnosis of ocular MG is established.
Medications for Ocular MG
Once the diagnosis of MG is established, treatment for the ocular symptoms can be considered. The difficulty with any treatment plan for ocular symptoms is the variability of symptoms. Most MG patients with bothersome symptoms will start on pyridostigmine (mestinon). Pyridostigmine has advantages of being overall a safe medication, dosing that can be adjusted based on the severity of symptoms and its relatively quick onset of action. Diarrhea and muscle cramping are potential side effects. Medications to suppress the immune system are considered if symptoms do not improve with pyridostigmine. These immunosuppressants include prednisone, mycophenolate and azathioprine. Oral steroids like prednisone are commonly the first choice as these are very effective in resolving the ocular symptoms more so than other medications and are easily available. The difficulty in treatment lies in the fact that prolonged treatment with steroids results in significant side effects including an increase in blood sugars, blood pressure, and increased risk of bone loss (osteoporosis). Following the use of prednisone, other immunosuppressive agents like mycophenolate and azathioprine may be used.
These medications come with advantages and disadvantages.
Advantages:
- Ability to reduce dependence on steroids.
- Favorable long-term side effect profile compared to prednisone with less impact on weight, blood sugars, bone health, etc.
Disadvantages:
- Need for monthly monitoring of blood work when starting these medications.
- Greater cost compared with the cost of prednisone.
- Longer time on medication before realized improvement.
- It may not be as effective for the ocular symptoms as prednisone.
Additional Information
Intravenous immunoglobulins (IV Ig) and plasmapheresis are effective for generalized MG and typically not utilized for ocular MG. However, in rare cases, these treatments may be utilized on a case-by-case basis. Similarly, thymectomy has no clear role in ocular MG unless there is concern for an underlying tumor of the thymus gland or thymoma.
Other Treatment Options
Double vision (diplopia) can be treated by blocking the vision from one eye by placing an eye patch or covering one of the eyeglass lenses with scotch tape. Difficulties encountered with monocular occlusion include a decline in depth perception that may affect daily activities. Fortunately, over several months, the brain can adapt to depth perception with one eye, and returning to daily activities is possible. Prism in glasses or the elevation of the eyelid with a “ptosis crutch.” The difficulty in the application of prism in the glasses is that the double vision changes throughout the day and is related to fatigue. Prism therapy may be useful to limit rather than eliminate diplopia, but rarely is there a complete resolution of the diplopia with prism in the glasses. With a consistent pattern to the diplopia, using a prism in glasses is more successful in limiting the diplopia. Surgical treatment of the droopy eyelid is more challenging if there is variability in the eyelid position. Improvement in eyelid position may result in expanding peripheral vision to allow daily activities such as driving possible.
