Femtosecond facilitates 'big bubble'

Dr Buzzonetti, chief, Department of Ophthalmology, Bambino Gesù Hospital, Rome, Italy, described his new 'IntraBubble' technique in which he uses a proprietary femtosecond laser (IntraLase, Abbott Medical Optics) to create an intrastromal channel that is used as a pathway for the insertion of the air injection cannula.

Dr Buzzonetti reported results from a series of 13 keratoconic eyes in which he performed the IntraBubble technique. The rate of DALK was 100%, the big bubble was achieved in 10 (77%) cases, while microperforation occurred in three (23%) eyes. Follow-up was available until 1 month after surgery and showed mean spherical equivalent (SE) was –1.5 D, mean topographic astigmatism was 2.9 D, and mean best spectacle-corrected visual acuity (BSCVA) was 0.5 D.

"DALK using the IntraBubble technique assures the lamellar cut is created at a predefined corneal depth to reduce the risk of inadvertent perforation and should shorten the learning curve for the big bubble step so that more surgeons may be encouraged to perform this procedure and allow their patients to obtain the advantages of big bubble DALK," he emphasized.

"However, even if conversion to penetrating keratoplasty becomes necessary, the patients will still have the advantages of better apposition between donor and recipient because the full-thickness procedure was performed using the femtosecond laser to cut donor and host with a zig-zag incision," he added.

In the IntraBubble technique, the centre of the cornea is marked with a pen and then the femtosecond laser first is used to create an intrastromal channel that arrives at 50 μm above the thinnest point of the cornea as measured by Scheimpflug imaging (Pentacam, Oculus). The channel is made at a 30° angle and has a 25° arc length.

"An incorrect pachymetry [measurement] was the cause for two of the three IntraBubble cases where there was an intraoperative microperforation," Dr Buzzonetti reported.

Then, the femtosecond laser is used to make a full lamellar cut, 9.5 mm in diameter, at 100 μm above the thinnest corneal point and intersecting the intrastromal channel. At the same depth, the femtosecond laser is used to make a lamellar cut in a zig-zag pattern with an anterior diameter of 8.1 mm and posterior diameter of 8.9 mm.

After removing the lamella, the channel, which is relatively short, is extended as needed using a dissector and finally, air is injected using a 27-gauge smooth cannula to achieve the big bubble.

"The channel is easily recognized and if is too short, it can be extended with a pointed corneal dissector," Dr Buzzonetti said.

"Being at a predefined depth is a major advantage of this technique and it provides a pathway for injecting air close to the endothelium," he asserted. "Therefore, in the event of a partial bubble, the surgeon can easily find a lamellar plane for dissection."

The procedure is completed by perforating the bubble, removing the residual stroma by scissors and positioning the donor, which is sutured using 16 single stitches.