Changes of intraocular pressure after photorefractive keratectomy; a comparison between Goldmann applanation tonometry and dynamic contour tonometry

1-Photorefractive keratectomy: All the participants underwent this operation using the Planoscan method of the Technolas 217z laser platform (Bausch & Lomb, USA) with an optical zone diameter of 6.00 mm, repetition rate of 50 Hz and a flat top-beam profile with spot size of 2.00 mm. After prep and drep (i.e. disinfecting the eyelids and periocular area for 1 minute with povidone–iodine 10% solution, and having the eyes washed out with 20 mL of a balanced salt solution), the epithelium was removed with a hockey knife and photoablation performed. 2-Goldmann applanation tonometry: The procedure was performed according to the guidelines of the Eye Care Technology Forum. The tear film was stained by placing paper fluorescein strips in the lower conjunctival fornix. Goldmann applanation tonometer (AT 900, HS Inc., USA) was mounted on a slit lamp (YJ-5Z, OcuHealth Plus Inc, New York, USA) and its tonometer was calibrated according to the manufacture’s instructions. The tonometer tip was brought into contact with the corneal surface and the intraocular pressure was documented after applanating the corneal surface and adjusting knob of the tonometer. Measurements were repeated 3 times at 30 second intervals and the readings averaged. Before each reading, the measuring drum was reset to approximately 2 mm Hg. In the case of fluctuation of IOP during the cardiac pulse cycle, it was measured in the middle of the pulsation amplitude. 3-Dynamic contour tonometry: Dynamic contour tonometer (Pascal, Swiss Micro Technology, Switzerland) was mounted on the same slit-lamp and IOP measurement was accomplished according to the manufactures’ guidelines. The tonometer tip of this device, similar to that of the GAT, contacts the corneal surface. However, its correct positioning is indicated by an audible signal that changes in pitch with changes in the pressure detected. IOP measurement with DCT was repeated if the quality score was greater than 2. In all participants, Goldmann applanation tonometry was performed 5 minutes after Dynamic contour tonometry on the same day.