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Katherine Bickle, Jason D Marsack, Alyce D Alven, Stephanie Cox, Kelly K Nichols, Jason J Nichols; The Impact of a Low Humidity Environment on Ocular Scatter and Corneal Higher Order Aberrations. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2015.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the impact of exposure to a low humidity environment on background scatter in Shack-Hartmann aberrometry images and third, fourth, and total higher order corneal aberrations.
Forty-seven normal subjects were enrolled in a one-visit study (average age 27.8 ± 11.1 years; 80% female). The Topcon KR-1W instrument was utilized to obtain wavefront aberration measurements before and after one-hour exposure to a low humidity environment (17.95 ± 2.15 % average humidity). The measurements obtained included Shack-Hartmann spot patterns and root-meat-squared coefficients of third, fourth, and total higher order corneal aberrations. Data representing the right eye of 10 of the 47 subjects with the highest Ocular Surface Disease Index scores were selected for further subgroup analysis. One pre- and post-exposure aberrometry image was utilized for both scatter analysis (over 3.5mm) and aberration analysis (over 4.0mm). Comparison of pixel intensity distributions (0 (black)-255(white), 30976 pixels) pre- and post-exposure were used to assess scatter. Differences in higher order corneal aberrations and scatter median differences pre- and post-exposure were assessed with a paired t-test and a one-sample t-test, respectively.
The average third, fourth, and total higher corneal aberration values pre-exposure were 0.060µm, 0.058µm, and 0.086µm and post-exposure were 0.080µm, 0.052µm, and 0.097µm, respectively, which did not differ statistically (p = 0.12, p = 0.28, and p = 0.37, respectively). However, nine of the 10 subjects showed a shift towards lower pixel intensities post exposure to the low humidity environment. The median difference across the 10 eyes in the maximum exposure shift that occurred in the direction of lower pixel intensities was -781 (p = 0.004).
Although no higher order corneal aberration values were observed between pre- and post- exposure conditions in these normal subjects, there was a systematic change in pixel intensity distribution in the Shack-Hartmann images. This scatter in the Shack-Hartmann image is hypothesized to result from light scatter associated with a tear film that has been disrupted as a result of exposure to a low humidity environment.
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