Tonometric Changes of Latanoprost-Induced Intraocular Pressure Reduction after Photorefractive Keratectomy

To assess whether tonometric measurements of the drop in intraocular pressure (IOP) induced by 0.005% latanoprost are modified after photorefractive keratectomy (PRK). Data from 24 randomly selected eyes of 24 patients (12 men and 12 women, mean age +/- SD: 31.7 +/- 6.2 years) who were undergoing bilateral PRK for myopia (-6.38 +/- 2.26 D) were obtained. Objective refraction, central corneal thickness (CCT), anterior radius of corneal curvature (R), and IOP measurements at baseline and 24 hours after 1 drop of 0.005% latanoprost, were performed before and 6 months after PRK. All measured IOPs were recalculated by a correction factor for CCT and R and expressed as true IOP (IOPT) measurements. The mean CCT +/- SD was 544.58 +/- 36.03 and 463.21 +/- 38.59 micro m, and the anterior radius of corneal curvature was 7.73 +/- 0.26 and 8.33 +/- 0.37 mm, before and after PRK, respectively. The mean IOP at baseline was 15.8 +/- 2.92 and 12.23 +/- 2.37 mm Hg, and after latanoprost administration was 12.54 +/- 1.97 and 10.19 +/- 1.47 mm Hg, before and after PRK, respectively. The mean IOPT at baseline was 15.46 +/- 1.08 and 16.18 +/- 2.31 mm Hg, and after latanoprost administration was 11.85 +/- 1.56 and 12.96 +/- 1.71 mm Hg, before and after PRK, respectively. The mean IOP and IOPT reductions after latanoprost administration were, respectively, 3.25 +/- 1.66 and 3.61 +/- 1.7 mm Hg before PRK, and 2.03 +/- 1.42 and 3.22 +/- 1.79 mm Hg after PRK. Pre- and postoperative IOP reduction significantly differed (P < 0.001), but not IOPT. The effect of hypotensive drugs on IOP readings may be underestimated because of measurement errors due to CCT reduction and R increase after PRK for myopia. Misdiagnosis of reduced pharmacologic efficacy may be avoided if the measured IOP is corrected by a proper nomogram.