Goldmann applanation tonometry after myopic photorefractive keratectomy

Purpose: To determine the accuracy of applanation tonometry in patients with corneas thinned by photorefractive keratectomy, and to correlate corneal changes with tonometric readings. Methods: The intraocular pressure was measured with Goldmann applanation tonometry in 87 patients who underwent photorefractive keratectomy before and 1, 6 and 12 months after treatment. The treatments ranged from -1.5 to -14 diopters (mean = -7.6 ± 4.1 diopters) and the fellow eyes were used as controls. Results: In the treated eyes the intraocular pressure before surgery ranged from 11 to 26 mmHg (mean = 17.7 ± 2.8 mmHg). One month after surgery it ranged from 5 to 22 mmHg (mean = 11.9 ± 2.7 mmHg) with a significant underestimation (P = 1 x 10-33). Six months after surgery it ranged from 6 to 22 mmHg (mean = 12 ± 3 mmHg) with a significant underestimation (P = 5 x 10-30). Twelve months after surgery it ranged from 8 to 22 mmHg (mean = 12.7 ± 2.7 mmHg) with a significant underestimation (P = 5 x 10-31). Conclusions: A correcting factor should be applied when using applanation tonometry to measure intraocular pressure in patients who have undergone PRK.