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Andrew KC Lam, Ying Hon, Angel Wong, Jimmy Tse, Guo-Zhen Chen, Shu-Hao Lu, David C. C. Lam; Short-term orthokeratology on corneal tangent elastic modulus - a pilot study. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2400.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate changes in corneal tangent elastic modulus and other corneal biomechanics following short-term orthokeratology.
Seventeen Chinese subjects (age, 18-25 years) were fitted with orthokeratology (ortho-k) lenses for 1 month in both eyes. Their baseline spherical equivalent was between -2.13 and -4.38D with a corneal toricity within 2D. Subjective refraction and ocular measurements were monitored in 4 visits, namely at the baseline and after the first overnight wear, the first week, and first month of ortho-k treatment. Corneal topography and pachymetry were performed. The corneal tangent elastic modulus (E) was measured using a novel corneal indentation device. Corneal hysteresis (CH) and the corneal resistance factor (CRF) were measured using the Ocular Response Analyzer. All measurements were conducted in the morning. One eye from each subject with a better uncorrected visual acuity (UCVA) after 1 month of ortho-k treatment was used for analysis.
The mean spherical equivalent decreased from -3.15 +/- 0.72D at the baseline to -0.11 +/- 0.22D at 1 month, final UCVA -0.07 +/- 0.07. Significant corneal flattening (both the steepest and flattest meridians) was observed as quickly as after 1 night of ortho-k treatment (Friedman test, p<0.001). Similar rapid central corneal thinning was demonstrated (Repeated measures analysis of variance, RMANOVA, p<0.001). Compared with the baseline, the CRF decreased significantly throughout the ortho-k treatment (RMANOVA, p=0.001) (from 10.4 to 9.8mmHg, a reduction of 5.8%). No significant change was observed in CH (RMANOVA, p=0.066). A significant increase in E was observed (RMANOVA, p=0.001) (from 0.456 to 0.509MPa, an increase of 11.8%). No correlation was found between initial corneal tangent elastic modulus and the speed of myopia reduction.
Similar to previous studies, short-term ortho-k treatment altered corneal biomechanics in terms of the CRF with no change in CH. The increase in corneal tangent elastic modulus revealed a stiffer cornea from ortho-k treatment. Should corneal tangent elastic modulus be a more suitable parameter for evaluating the corneal response to ortho-k treatment requires more studies.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Corneal hysteresis and corneal resistance factor in ortho-k treatment. Each error bar indicates 1 standard deviation.
Corneal tangent elastic modulus in ortho-k treatment. Each error bar indicates 1 standard deviation.
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