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Ayeswarya Ravikumar, Jason D Marsack, Heather A Anderson; Variability of simulated keratometry measures in subjects with and without Down syndrome. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):528. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Individuals with Down syndrome (DS) are known to have steeper corneas and greater astigmatism as compared to the general population. In addition, their corneas demonstrate distortion characteristics similar to keratoconus which could result in increased variability in clinical measurements. This study investigates the variability of corneal astigmatism magnitude, steep keratometry (K) power and the flat K orientation of subjects with and without DS obtained with the Zeiss Atlas corneal topographer.
Corneal topography was obtained on 140 DS subjects and 138 controls (age range=7 to 59 years). Subjects with three corneal topography measures per eye were analyzed for this study (DS: n=108 (216 eyes), controls: n=133 (266 eyes)). Corneal astigmatism (calculated as the difference between steep and flat keratometry powers), steep K power and the flat K orientation was obtained. Variability of each parameter for the DS and control groups was defined as the group mean standard deviation of the three measures. For flat K orientation comparisons, only eyes with >0.50 DC of astigmatism were included (201 and 220 for DS and control eyes respectively). T-tests were performed to compare the mean standard deviations between DS and control eyes for each parameter.
Average variability in corneal astigmatism magnitude in DS eyes (0.30 ± 0.39DC, range 0 to 2.83 DC with 65.3% ≤ 0.25 DC and 87.0% ≤ 0.50 DC) was significantly greater (p <0.001) than control eyes (0.09 ± 0.06 DC, range 0 to 0.50 DC (100%)). Average variability in steep K power in DS eyes (0.33 ± 0.43D, range 0 to 3.75D with 60.65% ≤ 0.25 D and 83.80% ≤ 0.50 D) was significantly greater (p <0.001) than control eyes (0.09 ± 0.09 D, range 0 to 1.00D with 99.25% ≤ 0.50D). Average variability in flat K orientation in DS eyes (5.62 ± 5.89 degrees, range 0 to 60 degrees with 86.07% ≤ 10.00 degrees) was significantly greater (p <0.001) than control eyes (3.16 ± 3.01 degrees, range 0 to 30 degrees and 96.82% ≤ 10 degrees).
DS eyes showed more variability compared to controls for all parameters. Although differences were statistically significant, on average 86% of DS eyes had variability of astigmatism magnitude and steep K power ≤ 0.50 D and variability of flat K orientation ≤ 10 degrees, indicating tolerable clinical variability for the majority of the group.
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