February 2008

 

CATARACT/ IOL

 

Incision approaches differ


by Rich Daly EyeWorld Contributing Editor

   

Surgeons utilize differing blades and surgical techniques to get the post-op astigmatism reductions they seek

It is important that PCRIs are made in clear cornea and not in vascular tissue Source: Douglas D. Koch, M.D.

The reduction of post-op astigmatism after IOL implantation has become an important component of successful surgery, and surgeons have devised a variety of approaches to ensure favorable outcomes.

The addition of various types of incisions over the years has provided surgeons with another tool. These include limbal relaxing incisions (LRIs), peripheral corneal relaxing incisions (PCRI), or penetrating LRIs (PLRIs)—none of which require pachymetry.

Limbal relaxing incisions have become a growing area of interest for Mark Packer, M.D., clinical associate professor, Casey Eye Institute, Oregon Health & Science University, Portland. Although surgeons use different instruments for LRIs, he has obtained the most reproducible results—especially in thick corneas—by measuring pachymetry in the 10-mm optical zone and always cutting to 90% depth. In order to always reach 90% depth, Dr. Packer found a continuously variable depth blade is needed.

Dr. Packer worked with Mastel Precision (Rapid City, S.D.) using a series of blades with a 360-degree plate around the knife, to ensure he obtained a perpendicular cut and guarded at the depth he desired.

“Using diamond blades that are precisely ground and continuously adjustable for limbal relaxing incisions is a real advantage over using metal blades. Metal blades may or may not cut to the depth you want and cause tearing or stretching of tissue, which almost certainly ends up in an epithelial defect,” Dr. Packer said about his use of the PHD2 adjustable and Elite II (Mastel) blades.

For most patients, the approach has provided excellent outcomes, Dr. Packer said, including reducing their astigmatism to less than half a diopter. But for patients with corneas thicker than 700 microns measured at the 10-mm zone, the results are more variable.

“I don’t bother trying to recut those,” Dr. Packer said. “I just take them to the excimer laser if they regress after six weeks and stabilize. I just do LASIK because I know that will get them what they want.”

The challenge lies in the fact that many patients who want astigmatism correction also want presbyopia correction. However, presbyopia correction and astigmatism correction will not come from IOLs until a toric multifocal or toric accommodative implant become available. “So we’re really doing limbal relaxing incisions, which are convenient, effective, and inexpensive,” he said about the approach that provides him with a high reproducibility rate.

Peripheral corneal relaxing incisions

Douglas D. Koch, M.D., professor and the Allen, Mosbacher, and Law Chair in Ophthalmology, Baylor College of Medicine, Houston, normally performs PCRIs without pachymetry using a diamond blade set at 600 microns. He uses the Rubinstein (Acutome, Malvern, Pa.) and the PHD diamond blades at the end of surgery.

Although he has found it is possible to perform PCRIs at the beginning of the case, large incisions can destabilize the cornea somewhat, making it a bit more difficult to perform certain steps of the cataract procedure.

Dr. Koch has found the use of markers effective with both blades because they provide a guide to control the direction and shape of the incision. The incisions he prefers are arcuate cuts at the 9 to 9.5-mm zone.

“I like to perform the incisions in the clear cornea at around a 9-mm zone,” he said. “Incisions that cross or involve vessels tend to scar and regress.” Although some surgeons prefer incisions at the 8-mm zone because they are more effective, they also have a slightly greater risk of inducing irregular astigmatism, he said. Slightly shorter incisions are used in older patients. The challenge in these patients has been the difficulty of developing a detailed age specific nomogram, Dr. Koch said. However, older patients clearly respond “more aggressively,” likely because their collagen is more rigid.

If he needs to make a PCRI in the meridian of the cataract incision, Dr. Koch makes an incision 180 degrees away. He also sometimes extends the cataract incision with a PCRI at the end of the surgery. “However, a PCRI in the cataract incision can destabilize it, so I only do this if I feel that the wound has a long tunnel and is truly watertight,” Dr. Koch said.

He has developed a detailed nomogram to use in the eyes undergoing cataract surgery, and also in virgin eyes and eyes that have undergone prior PRK or LASIK.

His overall technique corrects approximately up to 2 to 2.5 D of with-the-rule-astigmatism and 2.5 to 3 D of against-the-rule astigmatism.

The early approach

Incisions at the end of surgery don’t provide the best results for everyone. Joel K. Shugar, M.D., medical director Nature Coast EyeCare Institute, Perry, Fla., performs arcuate keratotomy at the beginning of cataract cases. Dr. Shugar’s approach is in the 8-mm optical zone and creates one or more arcs, followed by a Langerman groove (or hinge) at the junction of clear cornea and limbus, temporally.

“In my experience, the 8-mm OZ is the ‘sweet spot,’ optimizing regularity of topography while minimizing the amount of tissue incised,” Dr. Shugar said. “Using a smaller OZ increases risk for irregular astigmatism, while using a larger OZ requires incising much more tissue—increasing foreign body sensation and risking wound gaping for longer arcs.”

He uses a rectangular trifacet blade and prefers an “Arc-T” blade handle. The use of arcuate cuts helps him avoid the irregular astigmatism and changes to the spherical equivalent that sometimes result from T-cuts.

In patients over 80 years old, Dr. Shugar uses a 500 micron depth rather than the 600 micron depth he regularly utilizes in younger patients. In addition, he uses longer arcs for a given amount of astigmatism among younger patients. In lieu of a nomogram, Dr. Shugar bases his approach on the patient’s age and topography.

Dr. Shugar does not use the cataract incision in making his LRIs. The Langerman groove has minimal astigmatic effect, and he doesn’t lengthen it to try to create more. The overall approach allows him to correct up to 4 to 5 D through the use of incisions.

Editors’ note: Drs. Packer and Shugar have no financial interests related to their comments. Dr. Koch has financial interests with ASICO (Westmont, Ill.) and Mastel (Rapid City, S.D.).

Contact information
Koch: dkoch@bcm.tmc.edu
Packer: 541-687-2110, mpacker@finemd.com
Shugar: stareyes@gtcom.net

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