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Srilatha Vantipalli, Jiasong Li, Manmohan Singh, Kirill Larin, Michael D Twa; Optical Coherence Elastography of the Deep Corneal Stroma after Rose Bengal Green light Crosslinking in Rabbit Corneas. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1133.
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© ARVO (1962-2015); The Authors (2016-present)
There are structural and biochemical differences between the anterior and posterior corneal stroma. It is not advisable to use conventional UV-Riboflavin cross-linking in the deep corneal stroma due to potential UV-induced endothelial cell toxicity. Here we evaluate the biomechanical effect of Rose Bengal Green Light Cross-linking (RGX) treatment on the deep corneal stroma measured using a custom-built optical coherence elastography (OCE) system.
OCE measurements (three conditions) were made at the corneal apex in vitro on 4 rabbit eyes: anterior surface after de-epithelialization, deep stroma (after trephination to 2/3rd corneal thickness) and after RGX treatment in the deep stroma. RGX was performed using 0.1% rose bengal solution for 20 minutes (one drop every 5 min) and 10 min green light irradiation (565nm, 0.25W/cm2). Dynamic tissue deformation responses were produced using a focal micro air pulse stimulator (150µm spot size, 1ms duration, and 4Pa; 0.03mmHg) and surface deformation was recorded using a phase-sensitive swept-source optical coherence tomography (OCT) imaging system. Tissue deformation responses were quantified as the relaxation rate (recovery from deformation) and shear wavefront propagation speed. Intraocular pressure was stabilized throughout testing (10mmHg) using a closed-loop micro infusion syringe pump control system.
Mean relaxation rate was 1.65 ± 0.4ms-1 and group velocity at the anterior surface was 1.02 ± 0.21m/s with an average corneal thickness of 642 ± 19.7µm. Relaxation rate at a depth of 2/3rd corneal thickness (224 ± 59µm) was greater (18.6%) after RGX treatment (1.88 ± 0.24ms-1) than in untreated tissue (1.58 ± 0.1ms-1). Group velocity was also greater (13.2%) post-treatment (1.01 ± 0.1m/s) than in untreated tissue (0.89 ± 0.07m/s). Faster recovery (higher relaxation rate) and greater group velocity is consistent with stiffer material properties.
Higher relaxation rate and faster group velocity demonstrate an increase in stiffness in the deep cornea with RGX treatment. This shows promise for future applications in lamellar keratoplasty and refractive surgery through modification of deep corneal biomechanical properties.
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