Influence of Refraction on Tonometric Readings After Photorefractive Keratectomy and Laser Assisted In Situ Keratomileusis

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Abstract
To determine the decrease of Goldmann tonometry after photorefractive keratectomy (PRK) and laser assisted in situ keratomileusis (LASIK) according to refraction prior to surgery. Prospective simultaneous comparative case series of 53 myopic eyes (53 patients) that underwent PRK and 50 (50 patients) that underwent LASIK using the Summit Excimed SVS plus (Summit Technology, Inc., Walthan, MA, U.S.A.). PRK and LASIK were subdivided by refractive error into two subgroups of more than or less than -5 diopters (D). Central tonometric readings were taken prior to surgery and 12 months after surgery. In LASIK and PRK subgroups of more than -5 D, 85.7% (24) and 69.6% (24), respectively, gave lower readings than those taken before surgery. In LASIK and PRK subgroups of less than -5 D, 77.3% (17) and 53.3% (16), respectively, gave lower readings. The difference between the two is significant (p < 0.001). Average tonometry falls by 2.8 mmHG in the LASIK subgroup of more than -5 D (p < 0.001) and by 2.8 mmHG in the LASIK subgroup of less than -5 D (p < 0.001) and by 1.7 mmHG in the PRK subgroup of more than -5 D (p < 0.010). In PRK subgroup of less than -5 D, the tonometric changes are not significant (p = 0.971). High previous refraction (in PRK) and technique used determines lower final tonometric readings, bringing about more frequent and significant decreases in LASIK than in PRK for errors of more than and less than -5 D.