E-F-Dalk: Cut Parameters For Hybrid Excimer And Femtosecond Laser Assisted Deep Anterior Lamellar Keratoplasty – Pilot Experimentation

Current generation corneal femtosecond lasers rely on applanation to control cut depth. Applanation of an ectatic cornea in laser assisted keratoplasty leads to distortion and irregular astigmatism. We aimed to explore whether excimer laser ring cuts could be programmed to intersect with a femtosecond lamellar cut to produce a perfectly circular outline to the host and donor anterior side cut in mushroom pattern laser assisted deep anterior lamellar keratoplasty (DALK) with the aim of minimising postoperative astigmatism.

University Hospital, Pilot experimentation

We used the Schwind Amaris 1050rs excimer laser (Schwind Eye Tech Solutions, Kleinostheim, Germany) in keratoplasty mode to cut 450-micron depth channels in porcine corneas (n=4). We treated the first two corneas with standard keratometry settings (K1=K2=43.5D) and transepithelial annular PTK (450-micron depth, 9.0mm outer diameter, 8.5mm inner diameter). We treated the second two corneas using a similar ablation pattern, but with exaggerated flat starting keratometry settings (K1=K2=8D) and with the transepithelial option box unticked. We then obtained MS39 sectional OCT images (CSO, Florence, Italy) of the laser cuts using a custom mount fitted to the base of the Baron anterior chamber.

All cuts were perfectly circular, but with an edge profile that tapered towards a concave curved base on the sectional images. Flat keratometry settings produced a sectional profile closer to the target rectangular shape, but were still tapering to a curved base to the cut channel. Test porcine corneas were oedematous, and fluid could be seen pooling in the base of the annular cut channel during ablation. 

Further experimentation, using human corneas prepared from organ culture with normal pre-operative tissue hydration, is required to explore the potential of combined excimer and femtolaser assisted DALK (E-F-DALK), but the perfect circular cut outline we observed is promising. Avoiding flat or curved applanation in laser assisted DALK may reduce post keratoplasty astigmatism.