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Srilatha Vantipalli, Jiasong Li, Manmohan Singh, Kirill Larin, Michael D Twa; Spatial Mapping of Corneal Biomechanical Properties with Optical Coherence Elastography after UV Cross-linking in the Rabbit. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3704. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Keratoectasia results from focal structural degeneration of the cornea, which in theory, precedes gross morphological distortion that is the current basis for clinical diagnosis. Optical coherence elastography imaging is evaluated here for the capability to identify focal spatial variations in tissue properties induced using a tissue model of UV corneal cross-linking.
Spatial variation in corneal tissue properties was induced by performing UV-riboflavin cross-linking on all but the central 2mm of the rabbit cornea (n=4): 0.1% Riboflavin in 20% Dextran solution with 30 minutes UV radiation (370nm, 3mW). Optical coherence elastography imaging was performed using high resolution, phase-sensitive swept source OCT (3nm axial displacement sensitivity, 30 kHz A-scan rate). A micro air pulse stimulator produced focal tissue stimulation (150µm spot size, 1ms duration, and 4Pa/0.03mmHg) every 0.5mm over a 4x4 mm grid located at the corneal center. The OCT imaging system recorded dynamic surface deformation at the point of stimulation. Initial negative surface deformation and positive recovery responses were quantified from the point-wise OCT phase profile images. Measurements of tissue deformation and recovery were compared between treated and untreated tissue regions to determine if differences in material properties were detectable.
The initial surface deformation rate was greater in the untreated region (mean/SD: -41 ± 12 µm/s) than in cross-linked tissue (-32 ± 11 µm/s), a difference of 22%. The surface recovery response rate was greater in cross-linked tissue (1.73 ± 0.29 m/s) than in untreated tissue (1.53 ± 0.23 m/s), a difference of 13%. Elastograms clearly show the untreated central treatment zone dimensions.
Cross-linked tissue was more resistant to initial surface deformation and showed faster recovery response to surface deformation consistent with stiffer material properties. Optical coherence elastography imaging with focal micro air pulse tissue stimulation has the capability to show spatial differences in tissue material properties and shows promise for future diagnostic use.
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