Femtosecond laser adds precision to incisional astigmatism correction techniques

VIENNA — Incisional techniques for correcting astigmatism, such as arcuate keratotomy, can benefit from the precision offered by femtosecond lasers, according to a surgeon speaking here.

"Arcuate keratotomy can be a good option for patients with low astigmatism, and we may improve the results by using a femtosecond laser, which allows us to perform perfect arcs at a predictable distance," said Dimitri Azar, MD, in a presentation at the joint meeting of the European Society of Ophthalmology and American Academy of Ophthalmology.

In performing arcuate keratotomy, corneal incisions are made and opened partially in correspondence with the steepest meridian. The incisions are then widened as needed at the slit lamp based on postoperative topography maps, which show how the astigmatism shifted in response to the incisions, Dr. Azar said.

"I keep a conservative approach and refine the result postoperatively. I place the topography maps upside down on the IntraLase (Advanced Medical Optics) screen to make sure that my arcuate cut and the astigmatism coincide," he said.

For patients with a higher degree of astigmatism, especially those with a flat meridian, Dr. Azar uses a laser arcuate resection technique, which involves creating intersecting arcuate cuts of different diameters to perform a wedge resection. The widest area of tissue removal corresponds with the flattest meridian and tapers in width and depth from that point in an arcuate fashion, he said. The relative decentration of the arcuate cuts is based on the radii of curvature and desired wedge width to be resected, he noted.

"Femtosecond laser resection allows easier, more controlled and more precise excision of tissue in width, length and depth," Dr. Azar said.

Wedge resection can be either unilateral or bilateral, but in this case, it is performed in two stages. "The first resection is performed where the cornea is flatter or where there has been a wound dehiscence at an earlier stage, [such as] after [penetrating keratoplasty]. After suturing, I wait for the results and see if I have to add a second procedure on the contralateral side," he said.

Dr. Azar used this laser arcuate resection technique in patients with severe post-keratoplasty astigmatism who had underwent corneal transplantation at least a decade earlier. At the time of astigmatic correction, the patients' grafts were well stabilized and their astigmatism was long-standing and stable.

However, final results can be difficult to predict before the wedge sutures are removed, Dr. Azar noted.

"We must aim at overcorrection at first because suture removal reduces the astigmatic correcting effect. A reduction of at least 10 D to 15 D for every 0.5-mm wedge [created] is normally obtained," he said.