Changes in measured intraocular pressure after hyperopic photorefractive keratectomy

Purpose; To investigate the effect of hyperopic photorefractive keratectomy (PRK) on intraocular pressure (IOP) measurements. Setting. University of Ottawa Eye Institute, Ottawa Hospital, Ottawa, Canad a, Methods: In this retrospective cohort study, IOP and central corneal thickn ess (COT) were measured preoperatively and at 1, 2, 3, 6, 12, 18, and 24 mo nths in 191 eyes that had hyperopic PRK with the VISX Star excimer laser. A ll corrections applied were between +1.00 and +6.50 diopters (D) of sphere and less than 3.75 D of cylinder, Results. At all postoperative examinations, the mean IOP in the hyperopic P RK group was 1.0 to 1.8 mm Hg lower than the preoperative IOP (P < 001). A large range of IOP changes was found across the population; eg, at 6 months , 49% of the eyes had a change in IOP from baseline of at least :+/-3 mm Hg , A mean reduction of 19 <mu>m of COT was found with pachymetry after surge ry (P <.001), The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or applied correction. Changes in IO P were strongly correlated with preoperative IOP at all time points and wit h preoperative OCT at 18 and 24 months (P <.001). After hyperopic PRK, the measured IOP was more likely to increase in patients with preoperative IOPs less than 14.5 mm Hg and more likely to decrease in patients with preopera tive IOPs above 14.5 mm Hg. Conclusion: Changes in IOP after hyperopic PRK were similar to changes afte r myopic PRK, despite only minimal changes in the OCT. This suggests that h yperopic PRK results in biomechanical effects that modify the elastic prope rties of the cornea beyond the changes in rigidity expected from central co rneal thinning. There was a strong negative correlation between the measure d preoperative IOP and the change in IOP postoperatively that was likely th e result of regression of the mean effect, J Cataract Refract Surg 2001; 27 :1254-1262 (C) 2001 ASCRS and ESCRS.