INTRAOCULAR-PRESSURE DECREASE AFTER LOCAL OCULAR COOLING IS UNDERESTIMATED BY APPLANATION TONOMETRY

Background: The effects of intense systemic or local cooling on aqueou s humor dynamics in animals are an increased total outflow facility an d a decreased aqueous flow. Few studies suggest that only vasoconstric tion of arteriolar segments of the episcleral vasculature may be the c ause for a decrease in intraocular pressure after local cooling in hum ans. Because corneal changes may have influenced such studies, the eff ect of local cooling was assessed in normal subjects. Methods: Intraoc ular pressure and corneal thickness were measured in 18 healthy human subjects before and after exposure of the right eye to both, an air st ream at 20 degrees C, and an air stream at 0 degrees C. Results: No si gnificant changes in IOP or corneal thickness occurred under 20 degree s C conditions. After local cooling, the mean corneal thickness increa sed from 0.52 +/- 0.01 mm to 0.57 +/- 0.02 mm (p < 0.001). Mean intrao cular pressure decreased from 13.8 +/- 2.9 mmHg to 12.9 +/- 3.1 mmHg ( p < 0.026). The observed decrease in IOP correlated significantly but negatively (R = - 0.53; p = 0.024) with the increase in corneal thickn ess, indicating that the cooling effect on IOP may be rather underesti mated. Conclusion: The eye is very sensitive to local cooling effects, which may, however, partially be masked by changes in corneal thickne ss.