This web site is no longer actively maintained. Please visit for up to date information.
Powered by Google
This Month
Ocular Surface Characteristics of the Asian Eye
Meeting Synopsis
Academy 2010
pective Analysis of Risk Factors Associated With Contact Lens Induced Inflammatory Events During Continuous Wear
Feature Review
Adequate tear mixing under a soft contact lens may play an important role in minimizing certain > more
Tell a friend
> Home
> About Us
> Affiliates
> Contact Us
> Disclaimer
> Site Map


The Silicone Hydrogels website is partially supported through an educational grant from CIBA VISION

Posters | Archive
March 2008


Does the high modulus of SiH affect the accuracy of tonometry taken directly over the lens?

Fabrizio Zerio, Luigi Lupelli, Luciana Zarrillu, Dipartimento di Optometria dell”Instituto “De Amicis” Via Galvani, Rome Italy


Purpose:  Several authors have reported that it is possible to measure the intraocular pressure (IOP) accurately and safely using Goldmann applanation tonometry over a thin soft hydrogel contact lens (CL).  This procedure could be very useful in case of continuous wear as it allows us to measure the pressure without removing the CL.  However silicone hydrogel (SH), the most common material for continuous wear, has a higher modulus that could affect the accuracy of the procedure.  The aim of this work was to compare the measure of IOP over the SH CL with the highest modulus available in the market versus a hydrogel CL.

Method:  Twenty-four healthy subjects (13 males and 11 females; mean age 40.4 year, SD 13.4) were studied.  Two measurements of IOP using Goldmann applanation tonometer were taken in each subject for both eyes (for a total of 48 eyes); one with a sph -1.50D lotrafilcon A and the other with a sph -1.50D hilafilcon A.  This latter kind of hydrogel daily disposable CL was chosen because, as previously assessed, it had given a good reliability respect to the standard procedure.  The sequence of the two measurements over the two CLs was always inverted in the eyes of the same subject.  A t-test for dependent sample was used.

Results:  No differences were found between the value of the IOP with hilafilcon A and with lotrafilcon A (t-0.46, p=0.64).

Conclusion:  The IOP recorded over a lotrafilcon A CL (the SH with the highest modulus available) was the same as that over the hilafilcon A CL.  Although in this case the higher modulus of the SH doesn’t seem to affect the final outcome, further studies are needed to verify if similar findings occur in case of positive or higher negative CL powers.

Download PDF of Poster:
Download - 369 KB
You will need Version 4 or later of Adobe Acrobat Reader to view some documents on this site. You can get the latest version from the Adobe Home site. 
All rights reserved, copyright 2002 - 2007