CONTACT-LENS TRANSMISSIBILITY - EFFECTS ON DELIVERY OF OXYGEN TO THE CORNEA

The purpose of this study was to determine the effects of rigid contac t lens materials of various permeabilities and identical design on the oxygen shortfall of the human cornea and to explore differences in ox ygen 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 (cm(2)/s)(ml O-2/ml x mm Hg) a nd modulus of elasticity values from 1300 to 2200 MPa. Major results i nclude: (1) that the oxygen shortfall of the cornea decreased with inc reasing lens transmissibility under both static and dynamic conditions , with significant differences (p < 0.001) being demonstrated among ma terials; and (2) significantly larger differences (p < 0.001) between the static and dynamic condition data were seen for materials of low o k but were not predictable by lens modulus (p = 0.43, r(2) = 0.018). T he corneal demand differences between high and low Dk materials are po ssibly related to changes in corneal oxygen dynamics rather than to di fferences in tear exchange.