Contact lens transmissibility: effects on delivery of oxygen to the cornea

The purpose of this study was to determine the effects of rigid contact lens materials of various permeabilities and identical design on the oxygen shortfall of the human cornea and to explore differences in oxygen delivery to the cornea associated with contact lens materials of different modulus of elasticity values. Measurement of corneal oxygen uptake was performed for six human subjects under three conditions: (1) normal open eye; (2) after the static wear of six materials; and (3) after the dynamic wear of the same six materials. The 6 materials had Dk values that ranged from 0.02 to 127 (cm2/s)(ml O2/ml x mm Hg) and modulus of elasticity values from 1300 to 2200 MPa. Major results include: (1) that the oxygen shortfall of the cornea decreased with increasing lens transmissibility under both static and dynamic conditions, with significant differences (p < 0.001) being demonstrated among materials; and (2) significantly larger differences (p < 0.001) between the static and dynamic condition data were seen for materials of low Dk but were not predictable by lens modulus (p = 0.43, r2 = 0.018). The corneal demand differences between high and low Dk materials are possibly related to changes in corneal oxygen dynamics rather than to differences in tear exchange.