Simultaneous topography-guided PRK with collagen crosslinking seems to offer promising early results for patients with keratoconus who are contact lens tolerant.
The technique is controversial because of corneal thinning, but 70% of patients achieved 20/40 or better uncorrected visual acuity postoperatively, said Simon P. Holland, MD, clinical professor, University of British Columbia, Vancouver.
Dr. Holland explained that they used a transepithelial laser to remove the epithelium. The topography-guided PRK was performed using T-CAT software modified by topographical neutralization. The crosslinking procedure that they performed was the standard technique. The time of ultraviolet irradiation was reduced to a mean of 15 minutes, according to Dr. Holland.
One of the problems with the crosslinking procedure alone is that the patients do not see much better postoperatively following the procedure than they did preoperatively, Dr. Holland noted. Combining topography-guided PRK with crosslinking offers improved vision also.
He recounted the case of a 20-year-old male who did not achieve a change in the best-corrected preoperative visual acuity, but did achieve a significant lessening of the refractive error. A second patient, a 19-year-old student, achieved a two-line increase in the best-corrected visual acuity (uncorrected visual acuity, 20/25) and the cone was well ablated after the procedure.
"Many of our patients achieved similar results," Dr. Holland said. "The classic manifest refraction with against-the-rule astigmatism improved."
One problem with the laser is that it usually induces more myopia, Dr. Holland noted and referred to as "a limiting factor" in thinner keratoconic corneas.
Thirty-two eyes completed 1 year of follow-up. Twenty-two eyes (70%) had 20/40 or better uncorrected visual acuity at the 6-month and 1-year evaluations. All patients had a best-corrected visual acuity of 20/40 or better. Four patients lost two lines of vision, and six patients gained more than two lines of vision. The level of astigmatism at the 1-year visit decreased from a mean of 2.6 D to 1 D, Dr. Holland said.
At 1 year, only about 25% of patients were using refractive correction and the symptoms had improved in almost all patients.
The procedure was associated with some complications. Three patients had delayed epithelial healing, which Dr. Holland said he believes can significantly affect the long-term results if not successfully managed.
An important complication in this group of patients was a case of herpetic keratitis that developed in a 20-year-old man who was contact lens intolerant and had no previous history of herpes simplex virus. Ten days postoperatively after the bandage contact lens was removed, he developed a dendritic lesion, and he was found to be positive for herpes simplex virus. He was treated with systemic and topical antiviral agents. The vision recovered to 20/25 corrected visual acuity and 20/30 uncorrected visual acuity after a second surgery to remove the scar. Because of this case, all patients now receive a 10-day course of prophylactic systemic and oral antiviral drugs before surgery.
"Despite the fact that this is a controversial procedure, we are achieving some satisfactory early results in these patients whose corneas are already thin," Dr. Holland said. "The degree of refractive correction is limited by the corneal thickness; however, 70% of our patients achieved 20/40 or better 6 months after surgery with most patients not requiring any correction.
"This is a novel technique that remains controversial because of the thinning of the cornea," he concluded.
Simon P. Holland, MDE-mail: firstname.lastname@example.org
David T.C. Lin, MD E-mail: email@example.com
Drs. Holland and Lin have no financial interest in the subject matter.