The stability of corneal topography in the post-blink interval

Abstract

Purpose: Videokeratoscopes provide a wealth of information about the topography of the ocular surface. While there have been numerous studies of the accuracy and precision of videokeratoscopes with inanimate test objects, little information exists on their precision (repeatability) for real eyes. Methods: To investigative the stability of the ocular surface in the inter-blink period, 10 subjects were recruited for videokeratoscopy. Tear break up time (TBUT) was measured and videokeratographs were acquired immediately post-blink, and again at 4 seconds, 8 seconds and 12 seconds post-blink. To permit statistical inferences to be drawn from the data, we acquired 24 videokeratographs for each of the four post-blink intervals. The videokeratograph data was interpolated to common coordinate system and an average and standard deviation map was derived for each post-blink condition. T-tests were used to test the significance of changes observed in the topography. Results: The instantaneous power standard deviation maps showed increasing variance toward the periphery, with most maps showing less than +/-0.5D of standard deviation (S.D.) in the central 4-5mm. The periphery showed greater variance, often reaching more than +/-1D S.D. at the edge of an 8mm diameter. When the 4, 8 and 12 second average maps were subtracted from the average map acquired immediately after blinking, regions of statistically significant (p<0.001) change were apparent in the upper and lower regions of the maps. The upper and lower bands of change were found to correlate with the natural position of the subjects’ lid margins. Conclusions: For normal eyes, the central regions of videokeratographs show high stability in the inter-blink period. However the upper and lower edges of 8mm diameter maps show statistically significant variability, which appears to be related to the effect of eyelid pressure. CR: None