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Janice Dias, Noel M. Ziebarth; Effect of Corneal Crosslinking on Anterior and Posterior Stromal Elasticity Assessed Ex Vivo by Atomic Force Microscopy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1523.
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To quantify the anterior and posterior stromal elasticity after crosslinking with ultraviolet light and riboflavin.
Four pairs of porcine eyes (< 2 days postmortem) were used for this study. The eyes were retrieved from an abattoir, placed in a bag filled with saline, and shipped to the laboratory overnight. Upon arrival, the epithelium was removed using a cotton swap, and the cornea was excised with a generous scleral rim and placed in 20% Dextran overnight to restore the cornea to physiological levels (550-800μm). One eye of each pair underwent crosslinking treatment and the contralateral eye served as the control. For the treated eye, one drop of 0.1% riboflavin solution (10mg riboflavin-5-phosphate in 10mL Dextran 20% solution) was placed on the cornea every 5 minutes for 30 minutes. The cornea was then irradiated for 30 minutes using UVA light (=378nm) with an irradiance of 3mW/cm2. During irradiation, one drop of the riboflavin solution was placed on the cornea every 5 minutes. Manual delamination of Bowman’s membrane was performed to expose the anterior stroma. Elasticity was then measured with a custom-built Atomic Force Microscope designed for mechanical testing of ophthalmic tissues. Afterwards, delamination was continued to access the posterior stromal region and elasticity measurements were repeated. Young’s modulus was calculated using the Hertz model for a spherical indenter.
Young’s modulus of the untreated anterior and posterior stroma ranged from 16kPa to 393kPa and 8.4kPa to 57.1kPa, respectively. Young’s modulus of the treated anterior and posterior stroma ranged from 20.2kPa to 333kPa and 13.4kPa to 85.7kPa, respectively. The anterior stroma is consistently stiffer than the posterior stroma for both untreated and treated eyes. Corneal crosslinking resulted in a much greater increase in posterior stromal stiffness than anterior.
The effect of corneal crosslinking on stromal elasticity appears to be depth dependent.
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