Final answer:
The inability to abduct the eye in thyroid ophthalmopathy is often due to the immune system's attack on orbital tissues, leading to inflammation, enlargement, and fibrosis of the extraocular muscles, specifically the lateral rectus muscle, which impedes its movement.
Step-by-step explanation:
The inability to abduct the eye in a patient with thyroid ophthalmopathy, specifically Graves' disease, is typically due to the pathology affecting the extraocular muscles involved in eye movement. Graves' ophthalmopathy is marked by inflammation and swelling in the orbit, causing proptosis (bulging of the eyes) and restrictive myopathy, where the muscles become fibrotic and their movements are restricted.
In particular, the lateral rectus muscle, which is responsible for abduction of the eye, can become restricted or its movement hindered due to these changes. This can result in a variety of symptoms, such as diplopia or double vision, especially when attempting to look laterally. The pathological mechanism involves the immune system attacking tissues surrounding the eyes, leading to inflammation, glycosaminoglycan deposition, and muscle enlargement or fibrosis which in turn can impair the functions of muscles like the lateral rectus.