Extraocular muscle autoimmunity and orbital fat inflammation in thyroid-associated ophthalmopathy

The immunological basis for the ophthalmopathy associated with Graves' hyperthyroidism is both poorly understood and controversial. The mechanism for its link with thyroid autoimmunity is unknown but likely to be due to autoimmunity against some thyroid and orbital tissue-shared antigen, such as the thyroid-stimulating hormone receptor, which is expressed on the orbital pre-adipocyte and extraocular muscle cell, or the putative 'eye muscle cell membrane antigen'. Chronic upper-eyelid retraction, which sometimes occurs as a dominant feature of ophthalmopathy or as an isolated abnormality, is a common and related orbital disorder. Recent evidence that antibodies targeting the calcium-binding protein calsequestrin are specific and sensitive markers of eye muscle and upper-eyelid muscle damage has highlighted the need for diagnostic antibody tests in ophthalmopathy. In the context of this confusion, this review will address the nature of the autoimmune reactions in thyroid-associated ophthalmopathy, focusing on the eye muscle.