Photophobia / Light Sensitivity

Myasthenia gravis (MG) is an autoimmune disease that causes muscle weakness. One of the symptoms of MG is light sensitivity, officially called photophobia. This can cause a strong dislike of bright lights, or pain in the eyes when looking at bright lights.^1,2

MG can affect the eye muscles. Eye muscles include muscles that are responsible for moving the eyes as well as the eyelids. In about 85 percent of people with MG, weakness in the eye muscles is the first symptom of MG.¹

Ocular MG is a type of MG that causes weakness only in the eye muscles. But in many people with MG, muscle weakness begins in the eye muscles and then spreads to other parts of the body. This is called generalized MG.¹

Weakness in the eye muscles due to MG can cause many different symptoms, including:³

• Sensitivity to bright lights
• Drooping eyelids
• Double vision
• Dry eyes
• Blurry vision
• Trouble opening or moving the eyes

How does light sensitivity affect people with MG?

Light sensitivity may affect many different parts of your everyday life. For example, it can make it difficult to:³

• Read
• Watch TV
• Use a phone, computer, or other digital screens
• Drive a car, especially with headlights at night

People with MG may notice their light sensitivity gets worse throughout the day. This is because MG causes the eye muscles to get tired easily. Since you constantly use your eye muscles during waking hours, eye symptoms may get worse as the day goes on. Resting your eyes throughout the day may help relieve some symptoms.⁴

How does MG cause photophobia?

Light sensitivity stems from how certain eye muscles help the eyes adjust to different levels of light. The dark part of the eye is called the iris. In the center of the iris is the pupil. Light enters the eyes through the pupil. The size of the pupil determines how much light enters the eyes.⁵

When you encounter bright lights, your pupils get smaller to allow less light to enter your eyes. In dim lighting, your pupils get bigger to allow more light to enter your eyes. This change in pupil size happens automatically. The size of the pupil is adjusted by the muscles in the iris. These muscles are called the iris sphincter muscles.⁵

MG can cause the muscles in the iris to get tired and weaken after being used. When your iris sphincter muscles get weak, they are not able to change the size of your pupils as the amount of light in your surroundings changes. If your pupils stay large under bright lights, more light can enter your eyes and cause light sensitivity.^4,5

How can I manage photophobia?

Here are some things you can try to help reduce light sensitivity:^2,6

• Wear sunglasses in bright light.
• Wear a hat or sun visors to shield your eyes.
• Use dimmer lights inside your home.
• Try to avoid bright, fluorescent lights.
• Use artificial tears to treat dry eyes.
• Rest your eyes throughout the day.

Getting treatment for MG can also help relieve some symptoms. Treatments for MG may include:^1,4

• Acetylcholinesterase inhibitors – These medicines stop the breakdown of acetylcholine. Acetylcholine is a chemical that passes messages from nerves to muscles and helps control muscle movement.
• Immunosuppressive therapy – This treatment involves using different drugs to stop your immune system from attacking your own body.
• Thymectomy – This is the surgical removal of the thymus gland. People with a certain type of MG and those with a tumor in the thymus gland may benefit from a thymectomy.