PURPOSE. The use of the piggyback contact lens system (combination lenses) has been shown to be an effective treatment method for keratoconic patients and patients with other types of central cornea surface irregularities. Here a detailed examination was completed to compare the oxygen supply to the cornea for different lens designs, either alone or in combination. METHOD. Corneal oxygen uptake rates were measured for the central cornea of ten human subjects with a polarographic electrode. Measurements were made for the normal open eye and following static (non-blinking) wear of a PMMA lens, a thin hydrogel (Bausch & Lomb Optima 38), a thick hydrogel (Coopervision Permalens), and a high DK silicone/hydrogel (Bausch & Lomb Purevision). Additional measurements were made following static and dynamic wear of the combination of PMMA with each of the three hydrogel lenses. The lenses were worn for five-minute intervals and five-minute rest periods were given between each measurement.
RESULTS. Repeated measures analysis of variance (ANOVA) revealed a significant difference in the mean oxygen uptake relative to air for the ten lens combinations (p<0.0001). Post-hoc comparisons revealed a significantly higher mean value for PMMA worn alone when compared to Purevision, Optima 38, Permalens, PMMA and Purevision worn together under dynamic conditions, and PMMA and Permalens worn together under dynamic conditions. In addition, the ANOVA analysis showed that there was not a significant difference between the mean oxygen uptake relative to air obtained under static conditions compared to dynamic conditions (p=0.1013).
CONCLUSIONS. The components of these systems do have an effect on the oxygen supply to the cornea when worn alone or in combination. However, when worn in combination blinking does not improve the oxygen uptake relative to air.