Ocular surface drying and tear film osmolarity in thyroid eye disease

Five factors potentially associated with corneal exposure--palpebral fissure width, exophthalmos, blink rate, lagophthalmos, and lid lag--were evaluated in 17 patients with Graves' disease to determine which were associated with ocular surface damage. Multiple regression analysis revealed that increased palpebral fissure width and increased blink rate were both significant predictors of ocular surface damage (as measured by rose Bengal staining). Tear osmolarity and tear film break-up time were measured to determine the type of drying mechanism involved in thyroid eye disease. All eyes examined except one had blink rates adequate to prevent dry-spot formation. Fourteen of 33 eyes had abnormally high tear osmolarity. Increasing palpebral fissure width and increasing blink rate were both significant predictors of elevated osmolarity in tears obtained from the inferior marginal tear strip. We suspect that increased palpebral fissure width accelerates tear film evaporation, thus increasing tear film osmolarity with resultant ocular surface damage.