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Andrew KC Lam, Ying Hon, Shu-Hao Lu, Guo-Zhen Chen, David C.C. Lam; In vivo measurement of regional corneal stiffness. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4330.
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© ARVO (1962-2015); The Authors (2016-present)
To measure corneal stiffness at central and peripheral regions and to study effect from direction of gaze during peripheral measurement
Twenty-five young Chinese subjects (age, 21-26 years) had corneal stiffness measured using a corneal indentation device. It consisted of a 2-mm diameter indenter to measure the force required to indent at a 1-mm depth. Measurements were obtained randomly at the central cornea and 3mm from the temporal limbus. For temporal measurement, subjects maintained a primary fixation position and fixating 60-degree nasally. Corneal thickness at the center (CCT) and temporal (TCT) region were measured using swept-source anterior optical coherence tomography.
No significant between-eye difference in corneal thickness and corneal stiffness was found. Results from right eye were used for analysis. The mean central corneal stiffness was 0.070 (+/- 0.0065) N/mm. The mean temporal corneal stiffness was 0.074 (+/- 0.0074) N/mm at primary gaze, and 0.080 (+/- 0.0067) N/mm when looking nasally. Repeated measures ANOVA showed significant difference of the three results (F = 21.36, p < 0.001). Post hoc test revealed significant difference between central corneal stiffness and temporal corneal stiffness at primary fixation (p < 0.024). Since TCT was significantly thicker than CCT (paired t-test, t = -26.78, p < 0.001), corneal thickness difference at the two regions was set as covariate. The difference in corneal stiffness between the two regions was no longer significant (p = 0.692). Central corneal stiffness was positively associated with CCT (r = 0.48, p = 0.016), but correlation between temporal stiffness and temporal thickness was not significant (r = 0.23, p = 0.28). Post hoc test also revealed significant difference in temporal corneal stiffness at different direction of gaze (p < 0.007).
We demonstrated in vivo corneal stiffness measurement at different locations. A stiffer temporal cornea was due to its increased corneal thickness. However, there should be factors other than corneal thickness affecting peripheral corneal stiffness. Practitioner should be aware of effect from direction of gaze in peripheral corneal stiffness measurement.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1. Photographs of the corneal indentation device sitting on a slit-lamp unit.
Figure 2. a) A schematic diagram illustrates stiffness measurement at central cornea; b) at temporal cornea in primary gaze; c) at temporal cornea in nasal fixation.
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