Decrease in intraocular pressure following orthokeratology measured with a noncontact tonometer

Orthokeratology for correction of myopia reduces corneal power by flattening corneal curvature and thinning central corneal thickness (CCT). Measurement of intraocular pressure (IOP) with a noncontact tonometer is known to be affected by CCT and corneal curvature. We investigated the influence of orthokeratology on such measurements of IOP. This was a prospective, interventional case series derived from a clinical trial of orthokeratology lenses in two hospitals. Both eyes of 45 subjects were fitted with reverse-geometry lenses, worn for more than 4 h overnight for 52 weeks. Uncorrected visual acuity, refraction, IOP (with a noncontact tonometer), CCT, and corneal curvature were measured. Uncorrected visual acuity, spherical equivalent value, IOP, CCT, and the radius of corneal curvature were 0.93 +/- A 0.27, -2.87 +/- A 1.05 D, 13.5 +/- A 2.5 mmHg, 536.2 +/- A 39.6 mu m, and 7.88 +/- A 0.25 mm, respectively, before orthokeratology, and 0.17 +/- A 0.34, -1.05 +/- A 1.18 D, 12.4 +/- A 2.7 mmHg, 528.6 +/- A 40.8 mu m, and 8.10 +/- A 0.31 mm at 52 weeks after treatment. The changes in all parameters were significant, and the change in IOP was significantly correlated with that in CCT at 24 weeks and thereafter. Orthokeratology for myopia leads to a decrease in IOP measured with a noncontact tonometer, likely as a result of the associated decrease in CCT.