Corneal stromal effects and profiles with deep femtosecond laser ablations

Femtosecond laser ablation of the deep corneal stroma is a viable alternative to microkeratome donor preparation for DSAEK and DALK, Dr. Donald Tan told delegates on Saturday.

“There are only minor differences in stromal keratocyte reaction and interface inflammation between microkerotame and the femtosecond laser seen in our in-vivo rabbit eye model of deep lamellar dissection,” said Dr. Tan.

He said the results of his collaboration with Mario Nubile and his team in Italy showed that femtosecond stromal bed quality, rim cut quality, and accuracy of depth can now exceed the microkeratome for quality and accuracy.

Dr. Tan showed delegates a series of remarkable scanning electron microscope (SEM) microscopy images that illustrated the extreme precision offered by femtosecond ablation using the 200khz.

Tan and Dr. Nubile are currently testing the 500khz Visumax (Zeiss Meditech), which promises greater performance.

He said that Femtosecond laser provides a much more predictable ablation depth and diameter and also that endothelial surfaces showed a normal morphology when cut 150 microns from Descemet’s Membrane.

In his discussion Dr. Tan explained that applanating lasers caused some distortion on the posterior surface. Turning his examination to curved interface lasers, he showed that even when suction was lost during surgery, the quality of the cut was not compromised. “We deliberately induced suction loss in a rabbit series to see what effect it would have on cut quality. We found that when suction is lost, if the ophthalmologist reapplies suction and continues with the procedure there is no difference discernable - pristine flap lifts, no double layers.” He also believes that modern forms of lamellar corneal transplantation are transforming the field of corneal transplantation today. “Microkeratome-assisted lamellar dissection using Automated Lamellar Therapeutic Keratoplasty (ALTK) to prepare the posterior donor lamella is the current gold standard,” he declared.

However, he conceded that there are problems, including flap-related complications, such as incomplete flaps, variable thickness and diameter of donor, stromal bed ridges and irregularities and lenticular effects, such as a thicker periphery.

He noted potential femtosecond advantages include ease of surgery, improved stromal bed quality, better accuracy in depth of ablation, better donor edge quality - no restriction to shape and edge profiles and better lenticule profiles. The disadvantages include cost and poor laser penetration of corneal scars. He concluded by saying that femtosecond laser assisted forms of DSEK and DALK are now on the horizon.