Intraocular pressure and photorefractive keratectomy: A comparison of three different tonometers

Purpose. To evaluate the intraocular pressure (IOP) with three different instruments, Goldmann applanation tonometer (GAT), noncontact tonometer, and Tono-Pen after photorefractive keratectomy (PRK) for myopia. Methods. A prospective case series study to evaluate preoperative and postoperative IOP measurements of 149 eyes at 12 months. We performed GAT, noncontact tonometry, Tono-Pen central, and Tono-Pen temporal periphery measurements. We also performed measurements of the central corneal thickness (CCT) by ultrasonic pachymetry and keratometry. Preoperative IOP reading served as control for all studies. Results. After PRK, IOP reading was significantly reduced in the treated eyes when compared with the control measurements (11.87 ± 1.73 vs. 13.37 ± 1.52 mmHg, p < 0.0001 with GAT; 12.07 ± 1.6 vs. 13.51 ± 1.59 mmHg, p < 0.0001 with noncontact tonometer; 12.18 ± 1.6 vs. 13.48 ± 1.55 mmHg, p < 0.0001 with Tono-Pen central; 13.48 ± 1.65 vs. 13.71 ± 1.56 Hg, p < 0.0104 with Tono-Pen temporal periphery). There was also a significant correlation between IOP reading changes measured by GAT, noncontact tonometer, Tono-Pen central, and change of CCT and between reduction of IOP reading and keratometry (r² > 0.39, p < 0.0001 for each). The correlation between IOP reading change by Tono-Pen temporal periphery and CCT was also significant but r² value was only 0.034. Tono-Pen temporal periphery postoperative IOP measurements had the best correlation with preoperative GAT IOP (r² = 0.57, p < 0.0001). Conclusions. PRK reduced IOP reading as measured by GAT, noncontact tonometer, and Tono-Pen central; less so when measured by Tono-Pen temporal periphery. Early detection of glaucoma and IOP follow-up in glaucoma patients may be done best by peripheral Tono-Pen measurements over the nonablated cornea.