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PRK affected contrast sensitivity, glare performance in Air Force testing

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A significant drop-off in contrast sensitivity performance was seen after PRK in U.S. Air Force personnel, according to a recently published study. PRK did not appear to affect visual acuity in the study, but the contrast sensitivity changes might represent a true decline in visual performance, according to the study authors.

Richard J. Dennis, OD, MS, FAAO, and colleagues conducted a longitudinal clinical evaluation of the long-term effects of PRK on visual performance on 20 active nonflying Air Force personnel. Visual performance was measure at baseline and at 6, 12 and 24 months after PRK. Contrast sensitivity and VA data were collected by using the Freiburg Acuity and Contrast Test.

The participants viewed half of the testing through a polycarbonate windscreen. Experimental runs were conducted under three glare conditions: with no glare source, with a broadband glare source or with a green laser 532-nm glare source. The glare was projected as an annulus around the Landolt C stimulus.

Relative to baseline, no systemic effects of PRK on VA were identified, the authors said. With the laser glare source, VA was almost two full Snellen lines worse than with the broadband glare source. A significant drop-off was observed in contrast sensitivity performance after PRK under conditions of no glare and broadband glare. The authors noted that this drop-off occurred both with and without the windscreen. Laser glare disrupted contrast sensitivity performance significantly and more than broadband did, the authors said.

“The greater disruptive effects from laser vs. broadband glare may be a result of increased masking from coherent spatial noise (speckle) surrounding the laser stimulus,” the authors said. The study is published in the July issue of Optometry and Vision Science.