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R. Yanai, Y. Ishida, T. Sagara, K. Suzuki, T.-I. Chikama, T. Nishida, H. Toshida, A. Murakami; Underestimation of Intraocular Pressure After Orthokeratology. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1533.
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© ARVO (1962-2015); The Authors (2016-present)
Orthokeratology is a method for correction of mild myopia. It reduces corneal power by flattening corneal curvature and reducing central corneal thickness (CCT). Measurement of intraocular pressure (IOP) with a noncontact tonometer (NCT), which determines the time taken for a jet of air to induce corneal applanation, is dependent on CCT and the radius of corneal curvature. To investigate the possible effect of orthokeratology on IOP measurement with an NCT, we compared IOP values determined before and after this procedure. We also examined the relation between any change in IOP readings and changes in CCT or the radius of corneal curvature.
The study design was a prospective, interventional case series, and informed consent was obtained from each subject. Both eyes of 29 subjects were fitted with overnight reverse-geometry orthokeratology lenses, which were then worn for >4 h overnight. Subjects were free of ocular disease and had a corrected visual acuity of ≥ 1.0. Uncorrected visual acuity, refraction, IOP, and CCT were measured and keratometry was performed.
Before orthokeratology, uncorrected visual acuity, spherical equivalent value, IOP, mean radius of corneal curvature, and CCT were 0.16 (0.9 logMAR), -2.7 ± 1.00 (mean ± SD) D, 14.1 ± 2.7 mmHg, 7.91 ± 0.26 mm, and 540.2 ± 38.1 µm, respectively. After orthokeratology, the corresponding values were 1.06 (-0.01 logMAR), -0.27 ± 0.85 D, 12.3 ± 2.9 mmHg, 8.13 ± 0.30 mm, and 532.9 ± 43.1 µm. The changes in all parameters were statistically significant (P < 0.05). The change in IOP was significantly correlated with that in corneal curvature but not with that in CCT or spherical equivalent value.
Orthokeratology for myopia reduces NCT readings of IOP by flattening corneal curvature. Orthokeratology may thus result in underestimation of IOP.
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