The applicability of correction factor for corneal thickness on non-contact tonometer measured intraocular pressure in LASIK treated eyes

Abstract

PurposeTo determine the applicability of central corneal thickness (CCT) based correction factor for non-contact tonometer (NCT) measured intraocular pressure (IOP) readings. MethodA prospective, non-randomized study involved 346 eyes of 173 consecutive patients with age ⩾21years undergoing laser-assisted in situ keratomileusis (LASIK) for myopia and/or myopic astigmatism. The CCT and IOP were measured before and after the LASIK procedure. The IOP pre and post-LASIK was compared after applying the correction factor for CCT. Patients not completing the 3month postoperative follow-up were excluded. ResultsThe median spherical equivalent before undergoing LASIK was −4.25D (inter-quartile range, −3.25D). The mean preoperative CCT was 536.82±33.71μm which reduced to 477.55±39.3μm (p<0.01) post-LASIK. The mean IOP reduced from a preoperative value of 14.6±2.32mmHg to 10.64±2.45mmHg postoperatively (p<0.01). On applying correction for the corneal thickness, the pre and postoperative IOP was 15.14±2.8mmHg and 15.37±2.65mmHg (p=0.06) respectively with a strong positive correlation (r=0.7, p<0.01). Three hundred eyes (86.7%) had an absolute difference in IOP of less than 3.0mmHg post-CCT correction which is within the retest variability of NCT. Only 46 eyes (13.3%) had an absolute difference of more than 3.0mmHg. ConclusionThe modified Ehler’s correction algorithm used in this study can be effectively applied in the normal IOP range in a majority of patients.