New technique modification for CK gets better results

October 15, 2004

San Diego-A new technique for corneal marking and probe placement seems to improve the accuracy and standardization of probe placement in conductive keratoplasty (CK). This has translated into improved surgical outcomes, reported Charles H. Williamson, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

San Diego-A new technique for corneal marking and probe placement seems to improve the accuracy and standardization of probe placement in conductive keratoplasty (CK). This has translated into improved surgical outcomes, reported Charles H. Williamson, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

The CK probe is placed at the junctures of the ink marks, and in some cases, the treatment can result in obliteration of the ink mark, especially when stacked sequential treatments are made, said Dr. Williamson, medical director of the Williamson Nelson Eye Center, Baton Rouge, LA.

When he and his colleagues evaluated their early results, they found some variability in that there were overcorrections and increased astigmatism. When they changed the nomogram from the 6-mm optical zone to a 7-mm optical zone they got better results with use of more spots and larger ring sizes.

"Despite this, I believed that some problems might have been the result of the manner in which we were marking the cornea and placing the probe," Dr. Williamson said. "The metal markers, when measured, were not quite accurate, and they all required inking, which results in variations depending on the amount of ink on the marker, on the cornea, and the dryness of the cornea, among other factors."

Problems of current approach Other disadvantages of the present marking technology are the expense of the markers, the fact that the centering device and marking element can be damaged during autoclaving, and that the exact marking elements are not standardized from surgeon to surgeon.

"These disadvantages led to some poor precision and poor standardization in performing CK that was secondary to the present technique of marking," he said.

Considering these problems, Ron Dykes, instrument specialist, president of the division of International Science & Technology, Diamatrix, Woodlands, TX, designed a new injection-molded plastic marker that does not require inking.

The new marker is placed on a wet cornea, which eliminates the need to dry the cornea as when using an ink marker. Once the marker is pressed on the cornea, the marker produces all 32 marks that are long-lasting and readily visible.

Dr. Williamson demonstrated that, at the 7-mm optical zone, there are an additional 8 marks, which eliminates the guesswork from the procedure if 16 spots are used at the 7-mm optical zone.

The sharp-tipped probe can be placeddirectly in the depression that the marker creates, he said, adding to the accuracy of probe placement since the mark can be identified even with adjacent treatment.

Another change in Dr. Williamson's technique involves "dimpling" the cornea by pressing down on the probe until the cornea moves up around the tip, then backing off the pressure until the dimple no longer appears, then delivering the energy to the spot.

"This technique allows for more even, consistent energy transferred to the cornea," Williamson said.

"Using this new marker made the procedure more predictable from the standpoint of placing the probe correctly," he said. "We also believe that using this marker and technique improves our accuracy, and it may result in fewer problems with induced astigmatism and variable results from uneven energy and probe placement."