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Maolong Tang, Chenxing Zhang, Matthew Bald, Yan Li, David Huang; Laboratory Evaluation of Feasible Depths for Femtosecond Laser Assisted Lamellar Anterior Keratoplasty. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3124.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the cut depth that is useful for femtosecond laser assisted lamellar anterior keratoplasty (femto-LALAK).
Twenty human cadaver corneas underwent femtosecond laser full lamellar cut after the epithelium was wiped off. The stromal cut depth (measured from Bowman’s layer) was 17-21% (100 µm, n=3), 31% (n=5), 35% (n=5), 38-40% (n=4) and 45-48% (n=3) of central corneal stromal thickness (not including epithelium). A 150 kHz laser (AMO iFS) was used, with lamellar cut energy set at 0.7 µJ and spot and line separations set at 6 and 7 µm. The cap and bed surfaces were assessed by subjective grading of scanning electron microscopy (SEM) images on a scale of 1-5 (1=best, 5=worst) by 2 masked observers. The ridge score evaluates macroscopic irregularity based on 27× magnification SEM. The roughness score evaluates microscopic irregularity based on 100× SEM. Cap and bed scores were averaged for each cut interface. Photography and optical coherence tomography were performed to evaluate graft-host match in simulated femto-LALAK.
The ridge score was correlated with the micron cut depth (p = 0.0078, R = 0.58), and even more strongly correlated with percent cut depth (p = 0.00024, R = 0.73). On average, the shallowest cuts (17-21%) had the least ridges (score = 1.25). The 31% cut depth produced significantly less ridges (score = 2.15) than deeper cuts (35% score = 3.30, 38-40% score =3.25, 45-48% score = 3.83, p<0.05). The roughness grading ranged from 2.19 to 3.08 for various depths, without any systematic correlation. Simulated femto-LALAK using a 100 µm host lamellar cut and a 177 µm (31%) graft showed a smooth lamellar interface and flush anterior junction in an inverted side-cut design.
Femtosecond laser produced more ridges in deeper lamellar cuts. The amount of ridges correlated more closely to percent cut depth than micron cut depth. A depth setting of 31% stromal thickness may produce adequate surface quality for femto-LALAK designed to augment a keratoconic eye. The inverted side-cut design produced good edge apposition even when the graft is thicker than the host lamellar cut depth.
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