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W. J. Dupps, Jr., M. R. Ford, A. M. Rollins; Corneal Strain Mapping by Optical Coherence Elastography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3864.
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© ARVO (1962-2015); The Authors (2016-present)
To measure spatial differences in corneal displacement during a stress perturbation using a high-resolution optical imaging method for corneal biomechanical property measurement.
Paired human donor globes were imaged with a laboratory-based high-speed Fourier-domain optical coherence tomography scanner (OCT) while intraocular pressure (IOP) was decreased from 20 to 13±1 mmHg in replicate experiments. Pressure was directly controlled and monitored by intravitreal infusion. Scan frames included full-thickness, 3.3-mm widths of central cornea imaged with lateral and axial sampling densities of 4 and 8 microns, respectively. Two-dimensional patterns of optical feature flow over the stress decrement were analyzed with custom cross-correlation routines to derive displacement fields indicative of biomechanical strain. Three anterior and 3 axially corresponding posterior corneal 10x10-pixel regions of interest (ROI) were defined. Paired t-tests were used to compare displacement across ROIs in replicate experiments.
Axial displacements were much higher than lateral displacements during modest pressure decrements and differed significantly between eyes from the same donor (means for all ROI’s combined = 30.6±6.3 um and 52.5±10.2 um, p<0.001). In 4 of 5 ipsilateral replicate analyses, smaller displacements occurred in anterior stromal regions than in posterior stromal regions (mean difference 3.4 um), while differences between laterally seperated regions in the central 3.3 mm of the cornea were small. Displacement magnitudes within each ROI varied by less than 3 um (sd) on average during a single imaging sequence.
Optical coherence elastography is able to detect differences in the local response to a physiologic stress within and between individual eyes. Our initial results are consistent with existing anatomic and biomechanical evidence for greater material strength in the anterior stroma and much greater resistance to deformation in the lateral directions that correspond to the plane of collagen lamellar orientation. The capability to detect subtle spatial differences in strain behavior in individual eyes may provide more sensitivity for detecting ectasia, evaluating the biomechanical effects of surgical and pharmacologic interventions, accurately measuring IOP, and discerning preoperative material heterogeneity that could impact the optical response to surgery.
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