The measurement of intraocular pressure over positive soft contact lenses by rebound tonometry

Abstract

PurposeTo investigate if the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over disposable hydrogel (etafilcon A) contact lenses (CL) is affected by the positive power of the CLs.MethodsThe experimental group comprised 26 subjects, (8 male, 18 female). IOP measurements were undertaken on the subjects’ right eyes in random order using a Rebound Tonometer (ICare). The CLs had powers of +2.00 D and +6.00 D. Measurements were taken over each contact lens and also before and after the CLs had been worn.ResultsThe IOP measure obtained with both CLs was significantly lower compared to the value without CLs (t test; p < 0.001) but no significant difference was found between the two powers of CLs.ConclusionsRebound tonometry over positive hydrogel CLs leads to a certain degree of IOP underestimation. This result did not change for the two positive lenses used in the experiment, despite their large difference in power and therefore in lens thickness. Optometrists should bear this in mind when measuring IOP with the rebound tonometer over plus power contact lenses.

Rebound Tonometry over Soft Contact Lenses

“…Zeri published the data of comparison of mean IOP without CLs, with +2.00 dioptric CL power and +6.00 dioptric CL power. Mean IOP values in his study were 19.0±4.1 mmHg, 17.6±4.6 mmHg and 17.8±4.1 mmHg respectively ( 4 ). Nacaroglou ( 14 ) and Anton ( 15 ) have found in their studies that the measurements over CL by RT were found to be significantly higher than measurements without CLs, 15.68±3.75 mmHg vs. 14.50±3.41 mmHg (P <0.001) and 17.5±4.3 vs. 16.4±3.5 mmHg (P = 0.05) respectively.…”

“…On the other hand, rebound tonometers (RT) are used routinely for IOP measurements and do not require anaesthetic or fluorescein administration. Icare rebound tonometer became available in a year 2005 ( 3 , 4 ). Being a portable handheld tonometer, it is also mobile and independant of a slit lamp, which speeds up the process of the IOP measurement.…”