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Joel Palko, Xueliang Pan, Jun Liu; Effect of UVA-Rb cross-linking on through-thickness strains in canine corneas. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1615.
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Monitoring the mechanical changes of the cornea before and after corneal cross linking (CXL) provides valuable insight into CXL mechanisms and may help provide more personalized treatment plans for this therapy in the prevention of progressive keratoconus. The purpose of this study was to measure through-thickness strains in the cornea at physiologic IOPs before and after CXL using non-invasive ultrasound.
The anterior 3/4 of paired canine corneoscleral shells including a CXL treated group (n=6) and a control group (n=6) were mounted to a pressurization chamber within 10hrs of euthaniasia. The CXL group completed a standard clinical CXL protocol using riboflavin (Rb solution and UVA radiation (370nm, irradiance 3mW/cm2). Control eyes were given an identical Rb treatment without UVA irradiation. Cornea ultrasound scans (at 55 MHz) along the nasal-temporal (NT) and superior-inferior (SI) cross-sections were obtained before and after treatment as IOP was gradually increased from 5 mmHg to 45mmHg. Strain tracking was performed using a previously validated method (Tang & Liu, J. Biomech. Engrg 2012, 134(9)). Mean radial compressive strains and tangential tensile strains were calculated for the anterior, middle, and posterior one thirds of the cornea thickness in the nasal-temporal (NT) and superior-inferior (SI) directions. Mean strains at IOPs of 10, 20, and 30mmHg were compared between the CXL and control groups using mixed linear models with repeated measures.
Statistically significant reductions in tensile and compressive strains were found in the SI orientation at all three IOPs and all three layers in the CXL group (all p<0.05), with the exception of radial strains in the posterior third of the cornea. Similar mean strain reductions were found in the NT direction. The changes in the mean strains were small and not significant in the control group (p>0.05). The anterior third appeared to have larger tensile strain reduction than the posterior layer in the CXL group.
Ultrasound strain tracking revealed that the Rb-UVA CXL procedure significantly reduced corneal strains (i.e., stiffened the cornea) during physiologic IOP elevation with more pronounced effects observed in the anterior cornea. The ability to measure and monitor cornea strains may provide insight into the biomechanical effects of CXL and better define its role as a treatment for certain ocular disorders.
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