Bệnh nhược cơ mắt (OMG) là gì?

Ocular myasthenia gravis (OMG) is a subtype of bệnh nhược cơ (MG) characterized by the weakening of specific muscles responsible for regulating the movement of your eyes and eyelids. Unlike myasthenia gravis, which broadly affects the skeletal muscles you can control, in ocular myasthenia gravis, only muscles surrounding your eyes and eyelids are affected. Eye muscle weakness can result in ptosis (drooping of eyelids), diplopia (double vision), and blurry vision.

In about 20 – 60% of cases, ocular myasthenia gravis could progress to generalized myasthenia gravis, where muscle weakness develops in other body areas such as the arms, legs, or throat. 

In this article, we’ll discuss the basics of OMG, how it occurs, its symptoms, diagnosis, and effective treatment options. 

Basics of Ocular Myasthenia Gravis

Ocular myasthenia gravis is an autoimmune condition in which your immune system produces auto-antibodies that target and destroy the connection between nerve and muscle cells. 

Generally, when a healthy person wants to move or blink their eyes, the brain sends nerve impulses or signals. The nerve endings then release a substance called acetylcholine that attaches to its receptor on the ocular (eye) muscle and causes a muscle contraction. 

However, in OMG, the auto-antibodies block the acetylcholine receptor sites and thus prevent signals from reaching the eye muscles to contract. Consequently, the eye muscles tire easily. 

What Are the Common Symptoms?

People with OMG experience trouble with eyesight due to drooping eyelids or double vision. The eyes do not move together in balanced alignment, so a single object may be seen as two images instead of one. Similarly, when the eyelids droop and cover some or all of the eye pupil, it obstructs the field of vision. 

Eye weakness can change from day to day, and these symptoms can worsen if the eyes are strained for a prolonged period of time. However, eye weakness can temporarily be improved if you rest and close your eyes when your symptoms are troubling you.

People with ocular myasthenia gravis DO NOT experience trouble breathing, speaking, or swallowing, nor do they experience weakness in the arms or legs. 

How Is Ocular Myasthenia Gravis Diagnosed?

Diagnosis involves a combination of clinical evaluation, specialized tests, and a review of the patient’s medical history. The following are some tests that doctors conduct to diagnose OMG:

• Blood test to check for increased levels of autoantibodies
• Electrical nerve testing to record the electrical signals sent with muscle movement
• Repetitive nerve stimulation

How Can You Treat Ocular Myasthenia Gravis?

The treatments can vary from person to person and may depend on the severity of symptoms. 

In most cases, doctors would prescribe a class of medication called cholinesterase inhibitors like Mestinon (pyridostigmine bromide). The medication helps to increase levels of acetylcholine to send signals to the muscle to move. If this medication is not effective then oral steroids like prednisone or other immunosuppressants are recommended to suppress the immune system. Other treatment options include:

• Globulin miễn dịch tiêm tĩnh mạch (IVIG)
• Trao đổi huyết tương
• Biologic monoclonal antibody therapy
• Surgery  (thymectomy or  ptosis repair)

Overall, the prognosis is good, and the symptoms are manageable. 

Phần kết luận

Ocular myasthenia gravis is an autoimmune condition that affects the function of the muscles that control the movement of your eyes and eyelids. This results in eye problems such as double vision or drooping eyelids. However, once diagnosed and treated, medication can help manage the condition and improve the quality of life.