DALK preferred over PK, DSEK for keratoconus and secondary ectasia

A zigzag incision made with a femtosecond laser provides a strong and stable interface between the lamellar graft and recipient cornea, surgeon says.

Issue: April 25, 2012

Francis W. Price

Lamellar transplantation is the preferred transplant method for most patients with keratoconus or post-LASIK corneal ectasia, a surgeon said.

Complex incision designs generated with femtosecond lasers, such as the zigzag, enhance the safety and accuracy of deep anterior lamellar keratoplasty (DALK) performed on thin corneas, Francis W. Price Jr., MD, said during Refractive Subspecialty Day preceding the American Academy of Ophthalmology meeting in Orlando, Fla.

“I think that laser-assisted zigzag incisions are the way to go with thin corneas, either in keratoconus or post-refractive ectasia,” Dr. Price said. “This should allow more of our keratoconus and ectasia patients to have DALK instead of penetrating keratoplasty.”

DALK is preferable to PK because it enables the surgeon to preserve the corneal endothelium and reduce the risk of graft rejection. Patients who undergo PK also face an increased risk of IOP spikes and delayed healing attributed to corticosteroids used to prevent graft rejection.

PK has a high graft failure rate, even in eyes with keratoconus, Dr. Price said.

DALK is an invasive treatment for ectasia. Dr. Price recommended less invasive treatments such as rigid gas-permeable contact lenses, intracorneal rings and corneal cross-linking, unless the patient cannot wear contact lenses, has central corneal thickness of less than 300 µm or has significant corneal scarring.

Side cuts, lamellar dissection

“When we look at doing lamellar surgery, we have basic technique options for the side cut as well as for the lamellar dissection,” Dr. Price said. “For side cuts, we can do manual trephination, which basically gives us a vertical incision, or we can use femtosecond lasers to give us complex incision patterns.”

Femtosecond lasers are suited for performing side cuts, not lamellar dissection, Dr. Price said.

“To my knowledge, there’s no current femtosecond laser that can adequately perform a lamellar dissection in the posterior stroma,” he said. “I think you can understand that if you do endothelial keratoplasty. We know from stripping Descemet’s that the posterior stroma is very soft. The collagen alignment differs from that in the anterior stroma, and I just don’t think the lasers cut well there.”

Three technique options for lamellar dissection include hand dissection, the big bubble technique and the peeling technique.

Manual trephination is the standard of care but still has a few disadvantages, Dr. Price said.

“The big limitation is that with a manual trephination, it’s hard to precisely judge your depth when you’re making a cut with the metal blade,” he said. “And it’s hard to determine the appropriate depth with that incision when you want to do a hand dissection if you’re not doing a big bubble.”

Disadvantages of manual trephination also include the difficulty of cutting at a 90º angle at the desired depth when doing a hand dissection, Dr. Price said.

Zigzag incision

The zigzag incision is more accurate than a manual incision in terms of wound shape and depth, Dr. Price said.

A zigzag incision placed within 70 µm of Descemet’s membrane minimizes air escape into the periphery of the cornea in cases in which the big bubble technique is used, and it helps the surgeon gauge the depth when using a hand dissection technique, he said.

The zigzag incision has an interlocking tongue-and-groove wound configuration that seals the interface between the lamellar graft and recipient cornea. In addition, the interlocking wound edges improve the match between a thicker graft and a thinner recipient cornea compared with manual incisions, Dr. Price said.

“You put your donor on there and it is going to stick up higher than the edge of the recipient with a standard vertical incision,” Dr. Price said. “With the zigzag, that’s not a problem because the differing donor and recipient thicknesses come together and the zigzag shape helps align the anterior surface, resulting in a smooth transition. I think it gives us not only a smoother incision, but we have a much better wound construction that is stronger, and the contours look better.”

Additionally, a laser-cut incision allows a surgeon to perform deep dissection without a big bubble more easily, Dr. Price said.

“That’s much more difficult to do with a trephinated incision, at least in my hands,” he said. – by Matt Hasson

For more information:

Francis W. Price Jr., MD, can be reached at Price Vision Group, 9002 N. Meridian St., Suite 100, Indianapolis, IN 46260; 317-844-5530; fax: 317-844-5590; email: fprice@pricevisiongroup.net.
Disclosure: Dr. Price has no relevant financial disclosures.