Randomised controlled study comparing comfort-related outcomes between two rigid gas permeable (RGP) lenses with different sessile drop contact angles

Intrasession Repeatability of the Contact Angle Measured Using the Captive Bubble Method and Agreement Assessed Between Different Analysis Software Programs

OBJECTIVES

The material biocompatibility of hydrogel and silicone hydrogel (SiHy) contact lens (CL) is of paramount importance in CL wear because a decrease in CL wettability reduces wearer comfort and increases wearer dropout. The aim of this study is to report on the repeatability and agreement between two different software programs that measure the contact angle with the captive bubble method in marketed CLs, which will help to translate this information into clinical practice.

METHODS

The contact angle of 23 different CLs was measured with the captive bubble method using 2 software programs: FTÅ200 and ImageJ. Three consecutive measurements were conducted for each CL. Reproducibility, repeatability, and agreement values were calculated according to the British Standards Institute and the International Organization for Standardization.

RESULTS

All methods showed good repeatability values in both CL materials (coefficient of variation <1.51%, Sw <2.26°, intraclass correlation coefficient >0.89, and the range of limits of agreement was between 7.22° and 7.57°). Higher concordance was achieved between the spherical and nonspherical options when using FTÅ200 software than when using ImageJ software. Statistically significant differences (P<0.05) between the 2 software programs were found, and they ranged between 5° and 10°.

CONCLUSIONS

The captive bubble method showed great repeatability in measuring the contact angle in marketed CLs with both software programs (FTÅ200 and ImageJ) assessed in this study. However, differences in the measured contact angles suggest that these techniques are not interchangeable. Therefore, standardization is recommended for contact angle measurement in hydrogel CL materials to facilitate comparisons, to improve clinical use of this information, and to analyze their impact in CL user comfort.

Statistical guidelines for the analysis of data obtained from one or both eyes

PURPOSE

Measurements obtained from the right and left eye of a subject are often correlated whereas many statistical tests assume observations in a sample are independent. Hence, data collected from both eyes cannot be combined without taking this correlation into account. Current practice is reviewed with reference to articles published in three optometry journals, viz., Ophthalmic and Physiological Optics (OPO), Optometry and Vision Science (OVS), Clinical and Experimental Optometry (CEO) during the period 2009-2012.

RECENT FINDINGS

Of the 230 articles reviewed, 148/230 (64%) obtained data from one eye and 82/230 (36%) from both eyes. Of the 148 one-eye articles, the right eye, left eye, a randomly selected eye, the better eye, the worse or diseased eye, or the dominant eye were all used as selection criteria. Of the 82 two-eye articles, the analysis utilized data from: (1) one eye only rejecting data from the adjacent eye, (2) both eyes separately, (3) both eyes taking into account the correlation between eyes, or (4) both eyes using one eye as a treated or diseased eye, the other acting as a control. In a proportion of studies, data were combined from both eyes without correction.

SUMMARY

It is suggested that: (1) investigators should consider whether it is advantageous to collect data from both eyes, (2) if one eye is studied and both are eligible, then it should be chosen at random, and (3) two-eye data can be analysed incorporating eyes as a 'within subjects' factor.