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Dynamic ultra high speed Scheimpflug imaging for assessing corneal biomechanical properties101Figure 3: Selected Scheimpflug image frames of a normal cornea during the measurementin the radius of curvature at highest concavity in those subjectswho received treatment, consistent with increased stiffness.Subjects in the sham group showed no difference (p = 0.6981) atone month. Greater negative magnitude in the radius of curvatureafter corneal collagen crosslinking or a flatter curvature atmaximum deformation was observed.DISCUSSIONFigure 4: Graphic display report of a normal thin (A) and mildkeratoconic cornea; (B) with the deformation amplitude and cornealvelocity plots versus time(AL) and corneal velocities (CVel) are recorded during ingoingand outgoing phases. Corneal thickness is also calculated throughthe horizontal Scheimpflug image. The lowest value is displayed.RESULTSFigures 3 and 4 summarize the Corvis ST findings in a normalthin cornea (Figures 3A and 4A), compared to one with mildkeratoconus (Figures 3B and 4B). Both corneas have relativelysimilar central corneal thickness of 500µm and similar IOP of14mmHg . The deformation of the ectatic cornea is morepronounced, having higher DA and corneal velocities. Theapplanation lengths in the ectatic cornea are smaller.Such parameters have been found useful for the diagnosisof ectasia (2) , as well as for assessing CXL results (Roberts,unpublished data 2011). In the FDA trial of corneal collagencrosslinking conducted at The Ohio State University, subjectswere evaluated biomechanically using the Corvis ST before andafter the procedure. 11 keratoconic subjects randomly selectedfor the treatment group, were compared with 8 keratoconicsubjects randomly selected to be in the sham group. At one monthpost-procedure, a significant difference (p < 0.0014) was foundWe have described a new technique for the non-invasiveimaging of the dynamic response of the cornea to an air puffduring NCT, using UHS Scheimpflug imaging. The inspection ofthe corneal slit during the deformation allows for objective andsubjective analysis. The different corneal responses to the samedeformation stimuli obtained with the normal thin and mildkeratoconic cornea indicate that there are significant differencesin biomechanical properties despite these corneas having similarthickness. The relative contribution of intraocular pressure inthe measurement is relatively eliminated in the example, as botheyes have similar IOP. In addition, the ability to evaluate thedeformation response has the potential for demonstrating clinicalevidence for biomechanically evaluating the effect of collagencrosslinking procedure. 20The retrieved data and deformation obtained by theCorvis ST provide information related to the biomechanicalproperties of the tissue, including elasticity andviscoelasticity. Very importantly, the deformation data mayallow for more precise intraocular pressure measurements,which is also a significant influent of the deformationresponse. Therefore, the ultimate goal to understand thebiomechanical properties of the corneal tissue and to measureIOP will have to be achieved together.The generated parameters can be integrated using linearand/or more advanced artificial intelligence algorithms forimproving the accuracy of detecting disease and the impact ofsurgery. These parameters can be also used in combination withcorneal tomography and ocular biometry data.The integration of ultra-high-speed Scheimpflug imagingwith NCT has an enormous potential as a research and clinicaltool to retrieve in vivo biomechanical properties of the cornea.These measurements could be considered in finite element modelsthat would improve diagnosis and prognosis of corneal diseasesand improve safety and efficacy of corneal surgery.Rev Bras Oftalmol. 2013; 72 (2): 99-102