Differences In Noncontact Tonometry With And Without Soft Contact Lenses - Does Power / Center Thickness Make A Difference?

The use of the noncontact tonometer (NCT) has been proven effective and efficient for
measurement of the intraocular pressure without applanation to the cornea . Many practices utilize the NCT to reduce "chair" time by allowing the technician or assistant to take lOP (intraocular pressure) measurements prior to the examination. Furthermore, contact lens based practices realize how important exam time is for soft lens follow up patients. Intraocular pressure readings taken while wearing contact lenses saves time by eliminating costly insertion, removal , and stabilization periods. Pougiales, Jacobson, and Chumley were some of the first to try the technique in the late 1970's using conventional soft lenses.1 Since the introduction of thinner "disposable" lenses, other studies have investigated readings of different lens designs (i .e. lathed, spin cast) , water content, and lens thickness changes. It has been shown that a lens with a center thickness of less than 0.15 mm had no significant difference in pressure readings when compared to readings taken with no lenses at all.2 Since the center thickness is a major factor, changes in the lens power could affect the center thickness and the NCT results. lnsler and Robbins stud ied the effect of power changes on lOP readings by using thin extended wear myopic (B&L, CSI )and hyperopic (Coopervision) lenses. Their study reported significantly larger lOP readings for hyperopic lenses when compared to readings taken using myopic lenses.3 With ever-changing lens types evolving onto the market, we were interested in studying the NCT readings found over a frequently used planned replacement lens. A wide range of powers/center thicknesses were used to evaluate the accuracy and consistency of the pressure measurements. Several variables can influence the NCT reading over the lens, so we used only one lens type to help reduce any unwanted variables which could be attributed to differences in lens material or design. We chose a common NCT instrument (two AO Reichert II tonometers) and contact lens (Surevue) to help us determine if any significant differences were found when taking NCT readings over different lens powers/ center thicknesses of a commonly used frequent replacement lens.