Crowded Orbital Syndrome

Abstract

　Crowded orbital syndrome（COS）presents with divergence insufficiency esotropia or vertical strabismus without obvious oculomotor disturbances and is a mild form of strabismus fixus. Cases showing high myopia without the development of this strabismus are found to involve a large orbital volume. COS is thought to be caused by a mismatch between eye volume and orbital volume, i.e., the eyes are large relative to the orbit. Moreover, enlargement of the eye is more likely to occur within the orbit. Conversely, if there is a discrepancy between the volume of the eyeball and that of the orbit, the disease can develop in cases with a small orbit, even in eyes with a normal ocular axis. Although the disease has been shown to be associated with pulley abnormalities, it occurs even at a young age without age-related changes in the pulley, suggesting that the narrowing of the orbit may be a trigger for ocular position abnormalities.