Assessment of changes in corneal shape as a function of intraocular pressure: a pilot study

Purpose: To evaluate the effect of increased intraocular pressure (IOP) on the corneal shape of human cadaver eyes. Methods: Eight cadaver eyes, unsuitable for transplantation donated by the Florida Lions Eye Bank, were assessed for overall integrity. The epithelium was debrided, the eye placed into an artificial orbit, and a 30-gauge needle (connected to the IOP monitor) was inserted into the vitreous cavity. The IOP was altered as necessary by adjusting the height of the lactated ringers IV bottle. The surface contour was assessed at pressure levels: hypotony (2-4 mmHG), normal physiologic IOP (12-20 mmHg), hypertony (135-142 mmHg) and again at normal and low IOP. At each pressure level, two corneal topographic measurements (PAR CTSTM Vision Systems Corp.) were captured and averaged. Keratometric analysis was completed to examine the dioptric effects of varying IOP. An elevation analysis was performed to determine the corneal locations which conformed to the pressure adjustments. Results: The keratometric and elevation (both 0 and 90 degree meridians) data revealed decreasing radii with increasing IOP however, variability precluded statistical significance. Both keratometric and elevation data displayed probable plastic deformation, as the radii deviated from the original measurement upon the return to 2-4 mmHg. The elevation analysis did suggest an astigmatic conformation to pressure fluctuations, as 90 degree meridian radii were greater than 0 degree meridian radii. Corneal deformation is minimal in the 2 to 140 mmHg range and the PAR system not sensitive enough to accurately determine changes in curvature. Conclusion: The cornea does not uniformly conform to IOP variation. Further investigations with IOP levels of up to 500 mmHg will provide more information with respect to changes in curvature as a function of IOP.