Cornea - ARVO

ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group - CorneaProgram Number: 1615 Poster Board Number: D0250Presentation Time: 8:30 AM - 10:15 AMEffect of UVA-Rb cross-linking on through-thickness strains incanine corneasJoel Palko 1 , Xueliang Pan 2 , Jun Liu 3, 4 . 1 Wexner Medical Center,Ohio State University, Columbus, OH; 2 Center for Biostatistics, OhioState University, Columbus, OH; 3 Deprtment of BiomedicalEngineering, Ohio State University, Columbus, OH; 4 Department ofOphthalmology, Ohio State University, Columbus, OH.Purpose: Monitoring the mechanical changes of the cornea beforeand after corneal cross linking (CXL) provides valuable insight intoCXL mechanisms and may help provide more personalized treatmentplans for this therapy in the prevention of progressive keratoconus.The purpose of this study was to measure through-thickness strains inthe cornea at physiologic IOPs before and after CXL using noninvasiveultrasound.Methods: The anterior 3/4 of paired canine corneoscleral shellsincluding a CXL treated group (n=6) and a control group (n=6) weremounted to a pressurization chamber within 10hrs of euthaniasia. TheCXL group completed a standard clinical CXL protocol usingriboflavin (Rb solution and UVA radiation (370nm, irradiance3mW/cm2). Control eyes were given an identical Rb treatmentwithout UVA irradiation. Cornea ultrasound scans (at 55 MHz) alongthe nasal-temporal (NT) and superior-inferior (SI) cross-sectionswere obtained before and after treatment as IOP was graduallyincreased from 5 mmHg to 45mmHg. Strain tracking was performedusing a previously validated method (Tang & Liu, J. Biomech. Engrg2012, 134(9)). Mean radial compressive strains and tangential tensilestrains were calculated for the anterior, middle, and posterior onethirds of the cornea thickness in the nasal-temporal (NT) andsuperior-inferior (SI) directions. Mean strains at IOPs of 10, 20, and30mmHg were compared between the CXL and control groups usingmixed linear models with repeated measures.Results: Statistically significant reductions in tensile andcompressive strains were found in the SI orientation at all three IOPsand all three layers in the CXL group (all p0.05). The anterior third appeared to have larger tensile strainreduction than the posterior layer in the CXL group.Conclusions: Ultrasound strain tracking revealed that the Rb-UVACXL procedure significantly reduced corneal strains (i.e., stiffenedthe cornea) during physiologic IOP elevation with more pronouncedeffects observed in the anterior cornea. The ability to measure andmonitor cornea strains may provide insight into the biomechanicaleffects of CXL and better define its role as a treatment for certainocular disorders.Commercial Relationships: Joel Palko, None; Xueliang Pan,None; Jun Liu, NoneSupport: NIHRO1EY020929 (JL), Ohio State University College ofMedicine (JP)Program Number: 1616 Poster Board Number: D0251Presentation Time: 8:30 AM - 10:15 AMIn Vivo Evaluation of Corneal Biomechanical Properties AfterCorneal Collagen Cross-linking TherapyRaksha Urs 1 , Harriet Lloyd 1 , Ronald H. Silverman 1, 2 .1 Ophthalmology, Columbia University Medical Center, New York,NY; 2 Frederic L. Lizzi Center for Biomedical Engineering, RiversideResearch Institute, New York, NY.Purpose: Collagen cross-linking therapy (CXL) is emerging as atreatment option for keratoconus. This procedure strengthens thebiomechanical properties of the cornea by cross-linking the collagenbonds. However, biomechanical tests, to evaluate CXL outcome,have been performed only on ex vivo tissue. In vivo, the efficacy ofthe treatment is verified by assessing vision quality. The objective ofthis project is to demonstrate an in vivo technique to determinedifference in biomechanical strength of the cornea after CXL.Methods: CXL procedure was performed on the right eyes of 6rabbits. The left eyes were used as controls. Acoustic Radiation Force(ARF) was used to assess corneal stiffness in vivo, once beforetreatment (Baseline BL) and weekly for four weeks after treatment(W1-W4). Cornea was exposed to ARF using a single elementtransducer (25 MHz central frequency; 6 mm aperture; 18 mm focallength; Panametrics V324-SU). The beam sequence consisted of 20pushing tonebursts of 400 μs duration (80% duty cycle). Imagingimpulses were interleaved in the dead time to allow the sametransducer to acquire radiofrequency data during the push mode toimage corneal displacement. Acoustic power levels were withinFDA-specified levels for ophthalmic safety. Displacement of thefront and back surfaces of the cornea were used to determine thechange in corneal thickness and strain. ARF induced strain was fit tothe Kelvin-Voigt model to determine the elastic modulus. Theaverage moduli were calculated for the six rabbits, for each of thefive time points (BL, W1-W4).Results: At the end of four weeks, ARF measurements showed anincrease of average elastic modulus by 33% in the treated eye, and3% in the control eye. Paired t-tests revealed statistically significantdifferences between treated and untreated eyes from W1-W4(p=0.0005, 0.04, 0.0007, 0.006). There was no significant differencebetween right and left eyes before treatment (p=0.95).Conclusions: Our findings demonstrate statistically significantdifferences in stiffness between control and CXL-treated rabbitcorneas in vivo based on axial stress/strain measurements obtainedusing ARF. The capacity to non-invasively monitor corneal stiffnessoffers the potential for clinical monitoring of CXL. Longer term©2013, Copyright by the Association for Research in Vision and Ophthalmology, Inc., all rights reserved. Go to iovs.org to access the version of record. For permissionto reproduce any abstract, contact the ARVO Office at arvo@arvo.org.