The influence of orthokeratology on intraocular pressure measurements

Underestimation of IOP in a myopic patient may lead to misjudgment of the risk of glaucoma. This study investigated the influence of orthokeratology-induced change in CCT on IOP measured by the non-contact pneumotonometer (NCT), Goldmann applanation tonometer (GAT), and Pascal dynamic contour tonometer (PDCT).

This study was conducted to examine the eyes of 34 patients who received orthokeratology for myopia. CCT and IOP were measured, and IOP was obtained with the NCT, GAT, and PDCT. The associations between changes in measured IOP and change in CCT at different orthokeratology follow-up time points were evaluated by linear regression analysis.

Change in IOP measured by the three tonometries correlated significantly with change in CCT after one-week application of orthokeratology. The correlation was strongest for NCT followed by GAT and PDCT. The changes in measured IOP corresponding to a 10 μm decrease in CCT were 0.7-0.9, 0.4-0.6, and 0.2-0.3 mm Hg for NCT, GAT, and PDCT, respectively.

The IOP measured by the three methods--NCT, GAT, and PDCT--decreased as a result of the change in CCT induced by orthokeratology. The influence on NCT and GAT was greater than that on PDCT.