Humidity effects on corneal hydration.

Overall corneal hydration control expressed as the percent recovery per hour (PRPH) can be assessed with an exponential model that uses data derived from two kinds of corneal thickness measurements; one from monitoring recovery after inducing corneal swelling, and the other from measurements made after the eye has been open long enough to reach its open-eye steady-state (OESS) corneal thickness. Up to now these thickness measurements have been made without controlling the ambient humidity. It is possible that changes in relative humidity may effect tear film osmolarity sufficiently to change the state of corneal hydration. To evaluate the effects of humidity on hydration control, the OESS and PRPH were determined under several humidity levels. For both the OESS and the PRPH, two substudies were conducted. For the OESS, substudy 1 consisted of measuring corneal thickness when humidity was changed from 30% (ambient) to 52 or 97% controlled humidity. This resulted in mean +/- standard deviation (SD) changes in OESS thickness amounting to -0.33 +/- 3.5 microns and 2.6 +/- 3.4 microns, respectively, with a differential change of 2.94 +/- 3.04 microns (95% confidence interval [CI] from 0.77 to 5.11 microns). Corresponding results for substudy 2 connected with changes from 43% (ambient) to 12 or 97% controlled humidity were -2.4 +/- 2.7 microns and -0.3 +/- 1.9 microns, respectively, with a differential change of 2.1 +/- 1.8 microns (95% CI from 0.9 to 3.4 microns).(ABSTRACT TRUNCATED AT 250 WORDS)