What type of soft contact lens works best for reverse piggyback?

Aim To determine which type of soft contact lens works best in a reverse piggyback lens system. Background A reverse piggyback lens system comprises of a soft contact lens worn over a rigid gas permeable lens. Several uses of this system include prevention of rigid gas permeable lens decentration during sporting activities and reduction of rigid gas permeable lens intolerance due to lid sensitivity. Methods Four different types of soft contact lenses; Senofilcon A, Omafilcon A, Etafilcon A and Delefilcon A, were assessed in a reverse piggyback system, in both eyes of twelve subjects (n=24). Over refraction, best corrected visual acuity and comfort were measured for each lens. Comfort was assessed using a visual analogue scale. A LogMAR scale was used to determine best corrected visual acuity. These measurements were also conducted for rigid gas permeable lens wear alone. The results for over refraction, best corrected visual acuity and comfort were statistically analysed and interpreted with respect to change from baseline measurements of rigid gas permeable lens wear alone. Results Data for over refraction and best corrected visual acuity for each of the four lenses was tested to check for normal distribution using a Shapiro Wilk test. The data for over refraction was normally distributed for each lens, with the exception of Etafilcon A. However, as the frequency histogram for this lens appeared relatively normal, it was decided to proceed with a one-way ANOVA test to analyse the data for over refraction. The f-ratio value was found to be 0.19 (P=0.91). The data for change in best corrected visual acuity was not normally distributed. As the frequency histograms for this data did not resemble that of a normal distribution, a one-way ANOVA test could not be carried out. Instead, a Kruskal-Wallis test was utilised for statistical analysis of change in best corrected visual acuity. The H statistic was found to be 1.53 (P=0.68). The results for over refraction and best corrected visual acuity were not statistically significant at the 5% significance level. A Friedman test was used to analyse the data for comfort. The X2r statistic was found to be 9.01 (P=0.03). The differences in comfort between the lenses were found to be statistically significant at the 5% significance level. Re-analysis of the data using a Friedman test according to other researchers’ just noticeable difference estimations gave an X2r statistic of 5.37 (P=0.15). The differences in comfort between the lenses were not clinically significant at the 5% significance level. Conclusion There were no clinically significant differences in over refraction, best corrected visual acuity or comfort between each lens type. Therefore, a type of soft contact lens that works best for reverse piggyback was not identified. Further research with a larger sample size could be carried out to determine whether there is a lens which works best for reverse piggyback. However, if a lens was identified that works best for reverse piggyback, it may not be suitable in all cases due to the large amounts of individual variation indicated by the results