In Thyroid Eye Disease, which extraocular muscles are usually affected first?

• A. Superior rectus and inferior oblique
• B. Lateral rectus and superior oblique
• C. Inferior rectus and medial rectus
• D. Inferior oblique and lateral rectus

Answer: (C)

In thyroid eye disease, the pattern of extraocular muscle involvement reflects autoimmune inflammation that tends to hit certain muscles first. The inferior rectus is the muscle most commonly affected initially, and it is often seen together with the medial rectus. Swelling and eventual fibrosis of these two muscles restrict upward gaze and pull the eye inward, leading to diplopia and esotropia early in the disease. Other extraocular muscles may become involved later, but they are less commonly involved at the start. So, the muscles that are usually affected first are the inferior rectus and the medial rectus.