Factors influencing the measurement of oxygen shortfall of the human cornea: Sequencing of test conditions

Abstract 

Purpose

The effects of sequencing of test conditions, in this case contact lens thicknesses, on the measurement of the oxygen shortfall of human corneas were studied.

Methods

Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode on the central, unanesthetized right corneas of 14 human subjects. Measurements were made under the following conditions: (1) the normal open eye; (2) after 5min of static (without blinking) wear of each of seven rigid gas permeable lenses of seven center thicknesses (0.18, 0.12, 0.16, 0.20, 0.24, 0.28, and 0.32mm); (3) after 5min of static wear of a polymethylmethacrylate (PMMA) contact lens. Lens thicknesses were randomly assigned numbers, which were sequenced in seven cycles. Two subjects were assigned to each sequencing cycle, and each subject participated in two identical sessions.

Results

The interaction of order x thickness was determined to be insignificant (F=0.99; p=0.5101). The effect of lens order was also insignificant (F=0.76; p=0.6239), indicating that the order of lens placement did not affect the measured corneal oxygen shortfall. Not surprisingly, the analysis indicated a significant effect of lens thickness on corneal oxygen shortfall (F=3.94; p=0.0032).

Conclusions

The sequencing of lenses of various thicknesses on the cornea does not affect the measurement of corneal oxygen shortfall.

Keywords: Contact lens thickness, Corneal oxygen uptake, Rigid gas permeable contact lens