Abstract
Abstract: :
Purpose: To determine the effect of elevated intraocular pressure on keratometry. Methods: Fresh pig eyes were obtained less than four hours from slaughter from a local packing house. Eyes that were traumatized, damaged, or without clear corneas were excluded. Pig eyes were mounted in Styrofoam board by pinning ocular adnexa. An Orbscan® corneal topography image was taken of the cornea of the pig eye. See Figure 1. A Tonopen® was used to take the intraocular pressure (IOP) of the pig eye with a confidence level reading 95%. In the experimental group, 2 cubic centimeters of balanced salt solution were injected through a thirty gauge needle through the pars–plana. The control group had a thirty gauge needle inserted through the pars–plana and retracted without injection. A second corneal topography image was then taken without moving the eye from the mount. Finally, a second intraocular pressure measurement was taken with the Tonopen. This procedure was performed on a total of 32 test eyes and 14 control eyes. Data were analyzed statistically with a two tailed Z–test. Results: In the experimental group the IOP increased an average of 10.13±2.22 millimeters of water (p=0.01). In this group the average keratometry reading flattened 2.34±2.29 diopters (p<0.001). The axis of the steepest meridian changed an average of 15.81±38.24 degrees (p=0.05). Thirty out of 32 eyes, or 94%, showed corneal flatting by raising IOP. In the control group the IOP decreased an average of 1.86±1.07(p=0.01) millimeters of water between IOP measurements with needle insertion but no fluid injection. These corneas steepened an average of 0.46±2.17 diopters (p<0.001). The axis of the steepest meridian changed an average of 11.14±37.19 degrees (p=0.06). Ten out of 14 of eyes, or 71%, showed corneal steepening. Conclusions: By raising intraocular pressure in the experimental group of pig eyes, a definite trend existed in flattening the cornea. Conversely, the control group showed a slight steepening of corneas as this group lost a small amount of IOP. These fluctuations may change diurnal refractions and limit the ability to target refractive outcomes. Further studies need to be done on humans and with more physiologic fluctuations in IOP.
Keywords: optical properties • intraocular pressure • refractive surgery: corneal topography