Ocular rigidity evaluation after photorefractive keratectomy: An experimental study

PURPOSE: To evaluate possible changes of the ocular rigidity coefficient in vivo after photorefractive keratectomy (PRK) in a series of rabbit eyes, using an invasive ocular rigidity measurement device. METHODS: Sixteen eyes of 8 rabbits were used in this study. One eye from each rabbit underwent PRK for -10.00 diopters (D) in a 5-mm optical zone (92 mu m) while the fellow eye served as the control. Five weeks later, the rabbits were examined under general anesthesia. The pressure-volume relationship and the ocular rigidity coefficient were determined in all 16 eyes, by injecting 200 mu L of saline solution (in increments of 4.5 mu L) through the limbus into the anterior chamber, while the intraocular pressure (IOP) was continually monitored with a transducer, up to a maximum limit of 40 mmHg. Data within an IOP range of 10 to 40 mmHg were used to calculate the ocular rigidity coefficient. RESULTS: The preoperative central corneal thickness was comparable (P = .73, paired t test) in the pre-PRK eyes (mean: 347.5 +/- 17.11 mu m) and control eyes (mean: 349.1 +/- 17.46 mu m). No statistically significant difference was noted in measured ocular rigidity coefficient between eyes treated with PRK and control eyes (mean rigidity coefficient: 0.42 +/- 0.12 mmHg/mu L [range: 0.23 to 0.56] and 0.47 +/- 0.12 mmHg/mu L [range: 0.28 to 0.62], respectively, with 95% confidence interval of the difference, lower: -0.10 to upper: 0.015, P = .121). CONCLUSIONS: Photorefractive keratectomy did not significantly alter ocular rigidity measurements in this experimental model.