CHANGES IN EXTRAOCULAR-MUSCLE FUNCTION IN PATIENTS WITH THYROID-ASSOCIATED OPHTHALMOPATHY

Background:To determine the functional changes in the extraocular musc les in patients with thyroid-associated ophthalmopathy (TAO). Patients and methods: Horizontal saccades with an amplitude of 20 degrees were carried out over a period of 2 min. Eight patients with acute TAO and five patients with chronic TAO were compared with ten age-matched hea lthy individuals. Ocular movements were recorded using the ''Ober 2'' system based on infrared technology. For evaluation of fatigue effects , the parameters of the first five and the last five saccades were ana lysed. Results: A significant difference of four and five, respectivel y, out of nine tested saccadic variables including maximum velocity (V -max) was found both before and after fatigue. In comparison to normal subjects, patients with chronic TAO revealed mildly increased reducti on of V-max after fatigue. Results in patients with acute TAO were rel ated to the action of the most severely affected muscle. On active con traction of the medial rectus muscle (adducting saccades), V-max was n ot sign ificantly decreased after fatigue. On passive elongation of th e medial rectus muscle (abducting saccades), however, V-max was initia lly markedly decreased and increased significantly after fatigue. Conc lusions: Functional changes of extraocular muscles in patients with TA O can be demonstrated by saccadic analysis. The inverse change in velo city after fatigue in acute disease indicates an improvement of muscle elasticity during exertion and strongly supports the concept that ear ly impairment of bulbar motility in active TAO results from contractur e of myofilaments. Thus, analysis of the fatigue effect may help to di fferentiate between acute and chronic disease.