RESUMO
BACKGROUND: To determine the functional changes in the extraocular muscles 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 healthy 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 analysed. RESULTS: A significant difference of four and five, respectively, out of nine tested saccadic variables including maximum velocity (Vmax) was found both before and after fatigue. In comparison to normal subjects, patients with chronic TAO revealed mildly increased reduction of Vmax after fatigue. Results in patients with acute TAO were related to the action of the most severely affected muscle. On active contraction of the medial rectus muscle (adducting saccades), Vmax was not significantly decreased after fatigue. On passive elongation of the medial rectus muscle (abducting saccades), however, Vmax was initially markedly decreased and increased significantly after fatigue. CONCLUSIONS: Functional changes of extraocular muscles in patients with TAO can be demonstrated by saccadic analysis. The inverse change in velocity after fatigue in acute disease indicates an improvement of muscle elasticity during exertion and strongly supports the concept that early impairment of bulbar motility in active TAO results from contracture of myofilaments. Thus, analysis of the fatigue effect may help to differentiate between acute and chronic disease.
