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Srilatha Vantipalli, Jiasong Li, Manmohan Singh, Kirill Larin, Michael D Twa; Effect of Tonicity and UV Riboflavin Cross-linking Treatment on Corneal Biomechanical Properties using Optical Coherence Elastography. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© ARVO (1962-2015); The Authors (2016-present)
Current techniques to derive corneal biomechanical properties do not consider the influence of tissue hydration when measuring the effect of collagen cross-linking. Our previous studies with optical coherence elastography (OCE) show that corneal hydration and stiffness are positively correlated. Here we investigate the combined effect of hydration and UV riboflavin cross-linking (CXL) treatment in rabbit cornea.
Dynamic elastography imaging was performed using phase-sensitive optical coherence tomography (OCT) imaging (30 kHz A-scan rate) to quantify the tissue deformation dynamics resulting from a short-duration, spatially discrete, low-force air-pulse (150µm spot size; 1ms duration; 4Pa (0.03mmHg)). The viscoelastic tissue recovery response (relaxation rate; RR) was used to characterize the time-dependent surface deformation at the corneal apex. After epithelial debridement, fresh ex vivo globes with fixed IOP (15mmHg) were instilled isotonic riboflavin solution (n=6; 0.1% riboflavin in 2.5% dextran dissolved in PBS) and hypertonic riboflavin solution (n=7; 0.1% riboflavin in 20% dextran dissolved in PBS) every 5 min for 30min, followed by UV irradiation (365nm, 3mW/cm2) for 30min while instilling riboflavin. Central corneal thickness (CCT) was determined from structural OCT imaging and relaxation rates were determined from the OCE recorded viscoelastic recovery responses before and after CXL treatment.
Isotonic riboflavin did not affect CCT (P>.05) while hypertonic riboflavin caused a significant CCT decrease (30.6%; P=.01) from 618 ± 57.4µm to 428.7 ± 61.5µm. Isotonic CXL treatment showed significantly greater RR (10.3%; P=.01) after treatment (2.53 ± 0.1ms-1) than in untreated tissue (2.29 ± 0.1ms-1). However, hypertonic CXL treatment showed no change in RR (P>.05).
Faster recovery (higher RR) implies stiffer corneal material properties after isotonic CXL treatment. Hydration (tonicity) driven corneal thinning with hypertonic riboflavin caused a stiffness decrease that offset the expected stiffer material properties due to CXL treatment resulting in no change in corneal material properties after hypertonic CXL treatment. This demonstrates corneal hydration is an important factor in the measurement of corneal biomechanics that can confound short-term effects due to CXL treatment.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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