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. 2016 Jan-Mar;30(1):25-8.
doi: 10.1016/j.sjopt.2015.11.001. Epub 2015 Nov 19.

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

Jitendra Jethani  1 , Paaraj Dave  2 , Monica Jethani  3 , Yogesh Desai  3 , Purvi Patel  3
Affiliations

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

Jitendra Jethani et al. Saudi J Ophthalmol. 2016 Jan-Mar.

Abstract

Purpose: To determine the applicability of central corneal thickness (CCT) based correction factor for non-contact tonometer (NCT) measured intraocular pressure (IOP) readings.

Method: A prospective, non-randomized study involved 346 eyes of 173 consecutive patients with age ⩾21 years 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 3 month postoperative follow-up were excluded.

Results: The median spherical equivalent before undergoing LASIK was -4.25D (inter-quartile range, -3.25D). The mean preoperative CCT was 536.82 ± 33.71 μm which reduced to 477.55 ± 39.3 μm (p < 0.01) post-LASIK. The mean IOP reduced from a preoperative value of 14.6 ± 2.32 mmHg to 10.64 ± 2.45 mmHg postoperatively (p < 0.01). On applying correction for the corneal thickness, the pre and postoperative IOP was 15.14 ± 2.8 mmHg and 15.37 ± 2.65 mmHg (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 3.0 mmHg post-CCT correction which is within the retest variability of NCT. Only 46 eyes (13.3%) had an absolute difference of more than 3.0 mmHg.

Conclusion: The modified Ehler's correction algorithm used in this study can be effectively applied in the normal IOP range in a majority of patients.

Keywords: CCT; Correction; Intraocular pressure; LASIK; NCT.

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Figures

Figure 1
Figure 1
Scatter plot between the corrected pre and postoperative intraocular pressure with the regression line.
Figure 2
Figure 2
Scatter plot between the uncorrected pre and postoperative intraocular pressure with the regression line.
See this image and copyright information in PMC

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