Effect of corneal drying on optical coherence tomography.

Abstract

To determine the effect of corneal drying on the outcome of optical coherence tomography (OCT). Cohort study. Seventeen normal participants (mean age, 39+/-12 years). Subjects underwent a series of peripapillary circular StratusOCT scans (version 3.0; Carl Zeiss Meditec, Inc., Dublin, CA) in a randomly selected eye. Baseline scan sets were acquired, and thereafter, blinking was prevented by taping the eyelid. Eyelid taping was immediately followed by 6 to 8 serial scan sets, each separated by 20 seconds. After removing the eyelid tape, 3 additional scans were acquired at 1, 2, and 4 minutes of blinking freely. The analyzed outcome measures were scan quality as defined by signal-to-noise ratio (SNR) and signal strength (SS) provided by the built-in OCT software and mean nerve fiber layer (NFL) thickness. Significant reductions in SNR, SS, and NFL were noted at each scanning point in the drying phase (for each, P<0.015, paired t test) except for NFL thickness measurements acquired at 140 and 160 seconds. The reduction in NFL thickness exceeded the 95% confidence limit of the reported reproducibility error of StratusOCT after 15 seconds of corneal drying. After 1 and 2 minutes of blinking freely, there was still a significant reduction in NFL thickness compared with the baseline value, which was no longer evident at the 4-minute scan. Corneal dryness affects OCT scan quality and measured NFL thickness after a short exposure time. It is recommended to instruct those who are scanned to blink frequently or to instill artificial tears.