Accurate intraocular pressure measurement in contact lens wearers with normal pressures

The purpose of this study was to evaluate a modified technique of Goldmann applanation tonometry without the use of fluorescein or anesthesia in normal eyes with contact lenses and to compare this technique with Tono-Pen tonometry.

The intraocular pressure (IOP) of 40 normal eyes from 20 volunteers (mean age 25.6 years, range 22-35 years) was measured with and without-1.0 D disposable soft contact lenses in a prospective, masked, randomized study using Goldmann and Tono-Pen tonometry. Goldmann tonometry was performed without fluorescein or anesthesia with contact lenses on. IOP measurement using conventional Goldmann tonometry with fluorescein and without contact lens wear was employed as the standard for comparison.

Goldmann tonometry without fluorescein underestimated IOP levels in a consistent manner, with a bias of -2.15 mmHg (SD +/- 1.97). Goldmann tonometry without fluorescein, in the presence of a contact lens, consistently underestimated IOP levels by -2.90 mmHg (SD +/- 2.37), suggesting that IOP measurement is largely unaffected by the presence of a -1.00 D soft contact lens on the eye. In contrast, Tono-Pen tonometry consistently overestimated IOP levels by +3.93 mmHg (SD +/- 2.17). Given the limits of agreement, these results were fairly consistent.

The modified technique of Goldmann tonometry without fluorescein reflects standard Goldmann tonometry with fluorescein after a correction factor of +2 mmHg in normal eyes. IOP measurement by this technique does not appear to be significantly affected by the presence of a -1.0 D soft contact lens on the cornea.