Central and peripheral pressure measurements with the Goldmann tonometer and Tono-Pen after photorefractive keratectomy for myopia

Abstract

To compare the accuracy of Goldmann tonometry with that of the Tono-Pen(R) in measuring intraocular pressure (IOP) after photorefractive keratectomy (PRK). Eye Clinic, Cantonal Hospital, Lucerne, Switzerland.Thirty-five eyes (25 patients) had PRK for a mean myopia of -6.2 diopters +/- 2.6 (SD). Intraocular pressure (IOP) measurements were performed first with the Goldmann tonometer and then with the Tono-Pen in 2 corneal locations: centrally in the usual manner and temporally. For the temporal measurements, the patient was directed to gaze nasally as the tonometer was placed perpendicular to the temporal portion of the cornea and with the rim of the tonometer positioned just inside the limbus of the cornea. Subsequently, similar measurements were made with the Tono-Pen. Measurements were performed before and 1 and 3 months after PRK. Preoperative IOPs measured centrally and temporally were similar. After PRK, the central pressure readings with the Goldmann tonometer and the Tono-Pen were between 1.8 and 2.3 mm Hg lower than those measured temporally. The differences were statistically significant (P <.0001). Central corneal pressure readings obtained with either the Goldmann tonometer or the Tono-Pen after myopic PRK are inaccurate. Measurements over the temporal part of the cornea are likely more reliable.