Topography-Based RGP Lens Fitting in Normal Corneas: The Relevance of Eyelid and Tear Film Attributes

Abstract

The aim of this study was to investigate the influence of eyelid and tear film attributes on the ability of a topography-based contact lens-fitting module to correctly predict rigid gas permeable (RGP) contact lens parameters leading to successful in situ final lens fitting in normal corneas. A total of 28 healthy eyes with spherical refraction ranging from -2.00 to -6.00 D, refractive and anterior corneal astigmatism <-0.75 D and smooth keratometric mires were fitted with diagnostic trial tricurve RGP lenses as determined through simulated fluorescein pattern analysis. Modifications in the back optic zone radius (BOZR) and total diameter (TD) were implemented to the suggested parameters until a satisfactory fit was observed, whereupon the differences from the suggested parameters were recorded. Eyelid position, upper lid tonus, blinking completeness, tear film volume, and quality and corneal eccentricity were evaluated, and their relationship with the number of required parameter modifications was explored. Eyelid position and tear meniscus height presented a statistically significant association with the number of parameter changes between simulated and final in situ fittings. In addition, although eyelid position influenced both BOZR (rho=0.436; P=0.020) and TD (rho=-0.398; P=0.036), tear meniscus height only prompted TD modifications (rho=0.435; P=0.021). No additional associations were discovered and, on examining the direction of the modifications, no clear tendency could be detected. Eyelid position and tear meniscus height attributes, not taken into consideration by topography-based lens fitting software, influence RGP lens parameter selection.