Myasthenia gravis is a disorder that causes muscles to weaken and tire easily. The disorder can affect muscles that control eye and eyelid movement. The disease can affect the muscles of the face, eyes, arms, and legs. It can also affect the muscles used for chewing, swallowing, talking, and breathing. When it affects breathing, it is a life-threatening situation. Your ophthalmologist, working with a neurologist, will help determine the best treatment for your eye symptoms. The treatment will depend on the affected muscles and how weak these muscles are.