Eye muscle force development in thyroid-associated ophthalmopathy in different stages of disease

Ocular motility disturbances are common in patients with thyroid-associated ophthalmopathy (TAO). A quantitative evaluation of the isometric force of the eye muscles in TAO might be useful in the detection of early stages of this disease.

A total of 32 patients with TAO were divided into three groups according to whether they had mild active, pronounced, active, or longstanding, inactive disease. A group of six patients with Graves' disease without clinical signs of TAO and a group of 10 control subjects were also studied. The development of isometric force during saccadic eye movements of 5-, 10- and 20-degree amplitude in horizontal and vertical directions of gaze were recorded in the more affected eye in patients and the non-dominant eye in normal subjects, using a suction contact lens/strain gauge technique.

Peak tension (Fp) in vertical and horizontal saccadic movements was not significantly different between groups. Steady-state tension (Fs) was significantly higher in the groups with pronounced, active and longstanding, inactive disease than in the other groups for vertical (p < 0.01) and horizontal movements (p < 0.05). Abnormal force development in any of the gaze directions was seen in all patients with pronounced, active and longstanding, inactive TAO, and in some of the patients with mild, active TAO and Graves' disease without TAO.

Increased eye muscle tension was recorded in different gaze directions, confirming multiple extraocular muscle involvement in TAO. It is suggested that the increased force development reflected contractile compensations for restrictions of ocular motility due to higher muscle stiffness in thyroid-associated eye muscle disease. Tension measurements can be used to identify muscle involvement in TAO.