EFFECT OF PHOTOREFRACTIVE KERATECTOMY ON THE ACCURACY OF PNEUMATONOMETER READINGS IN RABBITS

Purpose. To determine whether measurement of intraocular pressure (IOP ) using a pneumatonometer is reliable after myopic 5 or 15 D excimer l aser photoablation in rabbits. Methods, Ten rabbits underwent 5 D myop ic photorefractive keratectomy (PRK) of the left eye, Another seven ra bbits underwent 15 D PRK. The right eye served as a control. The diame ter of each PRK was 5 mm. Rabbits were examined 2.5 to 3 months later under general anesthesia, Eyes were cannulated, and the IOP was mainta ined at 5 to 40 mm Hg and measured using an intracameral manometer and a pneumatonometer at each pressure level; approximately 50 pressure p oints were formed. Readings of the two techniques were compared. Resul ts. Linear regression analysis comparing manometric and pneumatonometr ic readings revealed the following data in eyes with 5 D corrections ( n = 10): correlation coefficient (1.) 0.926, slope = 1.058, and interc ept = -3.133. The values of the unoperated control eyes were: r = 0.90 0, slope = 0.962, and intercept = -1.010. The following results were o btained in eyes with 15 D photoablation (n = 7): r = 0.876, slope 1.13 3, and intercept -3.147, Values for the control eye were: r = 0.885, s lope = 1.175, and intercept = -3.497. When the manometer and pneumaton ometer readings of all animals were compared, the adjusted squared cor relation coefficient was 79%. When the variabilities associated with t he animals and the PRK procedure (pooled 5 and 15 D corrections) were taken into account, adjusted squared correlation coefficient increased from 8% to 87%. Conclusions. Photorefractive keratectomy as high as 1 5 D/5 mm had only a minor effect on pneumatonometer readings in rabbit s, indicating that the elastic properties of the cornea related to the accuracy of pneumatonometry were not significantly altered. postopera tive TOP monitoring with tonometers, based on Battening of the cornea under pressure, is accurate after PRK.