Tono-Pen versus Goldmann tonometry after excimer laser photorefractive keratectomy

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Abstract
To compare intraocular pressure (IOP) measurements by the Tono-Pen 2tonometer and Goldmann applanation tonometer (GAT) in post-photorefractive keratectomy (PRK) patients. Refractive Surgery Center, Assaf Harofeh Medical Center, Zerifin, Israel. In 18 patients, IOP was measured by GAT and then by Tono-Pen 2tonometer 2 to 18 months following PRK (mean 6.6 months ± 5.1 [SD]). Photorefractive keratectomy had been performed in 1 eye of each patient; the fellow eyes served as controls. Corneal curvature and thickness were evaluated. Ten of the 18 patients were treated with topical steroids. In the post-PRK eyes, mean GAT IOP was 1.8 ± 3.1 mm Hg lower than meanTono-Pen IOP (P = .012); there was no significant IOP difference in the control (fellow) eyes. In steroid-treated post-PRK eyes, mean GAT IOP (12.2 mm Hg) was 2.2 ± 1.3 mm Hg lower than mean Tono-Pen IOP (14.4 mm Hg) (P = .0007). Mean Tono-Pen IOP in steroid-treated post-PRK eyes was 4.3 ± 3 mm Hg higher than in the fellow eyes (P = .0014); mean GAT IOP was only 2.3 ± 3.5 mm Hg higher (P = .04). In post-PRK eyes without topical steroid treatment, mean GAT IOP was 2.0 ± 1.18 mm Hg lower than in the fellow eyes (P = .001); there was no significant difference in Tono-Pen OP. There was a negative correlation between the difference in IOP values (Tono-Pen minus GAT) and corneal curvature in post-PRK eyes (r = 0.76, P = .0108, n = 15). The Tono-Pen tonometer appeared to be less affected than the GAT by the relative flattening, thinning, and anterior stromal decreased rigidity of the central cornea that occur following PRK. Post-PRK steroid-induced IOP elevation may be masked by the artifactual decrease in GAT IOP.