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Corneal response and vision with the Softperm lens in simulated aircraft conditions
Background:
Contact lenses are generally more compatible than spectacles with the life-support systems, personal protective devices, and helmet-mounted targeting systems used in modern military aircraft. This study evaluated the Softperm contact lens in a simulated aircraft environment to determine its potential use by USAF aviators.
Methods:
Thirteen subjects wearing Softperm lenses were exposed to a simulated aircraft environment for 2 hours. Subjects were evaluated for signs of hypoxic stress by measuring corneal thickness changes and observing changes in corneal staining and conjunctival injection. Changes in visual acuity were also measured. Slit lamp biomicroscopy was used to assess lens movement at the beginning and end of the treatment period to determine if lens fit changed. Over-refractions to determine residual astigmatism were performed to evaluate how well the Softperm lens corrected astigmatic refractive errors.
Results:
A statistically significant increase in corneal thickness was found after two hours of Softperm wear in the simulated aircraft environment. Several subjects experienced an increase in epithelial staining, which appears to be associated with changes in lens fit (tightening). All subjects experienced conjunctival injection. Residual astigmatism secondary to lens flexure occurred in all but two eyes, but no eyes had greater than 0.75 diopters.
Conclusions:
When properly fitted, the Softperm lens can be safely worn in an aircraft environment similar to the one simulated in this study. This lens design may provide an alternative to the lenses presently approved for USAF aviators.