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R. Pertaub, D. Borja, H. Loree, D. Muller; Feasibility of Astigmatism Correction With Selective Thermal Treatment of the Anterior Cornea. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4217.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the feasibility of correcting low to moderate astigmatism via Keraflex (KFX), a microwave based approach to thermal keratoplasty, as evidenced by the ability to selectively induce astigmatism along a desired meridian in an ex vivo model.
Selective heating of the cornea with a segmented annular electrode was evaluated on 17 fresh intact ex vivo porcine globes (post mortem time < 1day). Asymmetric shrinkage lesions were induced at energies of 3-8J with 2 coaxial electrodes (5mm inner dia. x 200µm thick inner electrode and a 6.5mm outer dia. ground electrode). A groove segments the inner electrode to form two C-shaped heating zones, thus selectively flattening the anterior corneal surface along a desired meridian. Pre- and post-KFX corneal radii of curvature were assessed along 32 meridians about the optical axis from cross sectional Scheimpflug slit-lamp images, from which SimK refractive power was calculated. Pre-op and induced astigmatic error (Cylinder [D]), defined as power difference between steepest and flattest perpendicular meridians, as well as the post-KFX axis of flat (AoF) were analyzed.
Selective shrinkage of the corneal stroma flattens the total corneal surface within the central 8mm pupil diameter. The post-KFX astigmatism axis of flat corresponds well to the electrode groove axis (Post-KFX AoF [deg]=0.91*Groove Axis [deg], r=0.80 and p<0.0001). The post-KFX astigmatic error increased linearly with applied energy (Cylinder [D]=2.17*Energy[J], n=21, r=0.32 and p=0.03).
While KFX flattens the entire anterior cornea, the effect can be amplified along a desired meridian, adjusting both refractive power and AoF, showing promise for combined treatment of astigmatism and myopia error.
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