PURPOSE: To determine which ocular topography variables affect soft contact lens fit.
METHODS: Fifty subjects each wore three soft lenses in succession (Vistakon ACUVUE® 2 and Acuvue 2 [A2], Vistakon ACUVUE® ADVANCE™ [AA], Ciba Focus® NIGHT & DAY™ [N&D]) and various aspects of lens fit were evaluated. The steeper base curves of each type were worn in one eye and the flatter base curve in the other eye. Corneal topography data were collected using a Medmont E300 corneal topographer (Camberwell, Australia). As well as corneal curvature (CC) and shape factor (SF), corneal height (CH) was measured over a 10mm chord and also the maximum measurable diameter. These were measured in the horizontal (h), vertical (v), steepest and flattest meridians. Spearman's rank correlation coefficient was used to test for associations between lens fit and ocular variables. A P-value of 0.01 or less was taken to indicate a statistically significant correlation.
RESULTS: With each lens type, the steeper base curve provided the best fit on the greatest proportion of eyes. For each lens type, there was no significant difference in mean K-reading between those eyes best fit with the steeper base curve and those eyes best fit with the flatter base curve. All three lens types showed significant positive correlations between centration and both CHv and CHh (maximum), increasing CH resulted in greater decentration. With A2, there were also some negative correlations between centration and some of the SF measurements. Interestingly, there were no correlations between corneal topography and tightness on push-up or post-blink movement. The assessment of overall fit correlated with CH, and SF; better lens fit was associated with greater CHh and lower corneal asphericity (i.e. greater SFv & SFh). A correlation with comfort was noted with only one lens; poorer comfort with N&D was associated with greater CH.
CONCLUSIONS: The best-fit base curve is not predicted by keratometry. The most consistent correlation between lens fit and corneal topography is that between centration and corneal sagittal height.