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Keratectasia may not be long-term problem, speaker says
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LISBON, Portugal — A discrepancy between the expected rate of keratectasia after LASIK and the actual number of reported cases suggests that “there is probably not an epidemic of ectasia after LASIK,” said Patrick Condon, MCh, FRCS(Irl), FRCOphth.
Dr. Condon delivered the Ridley Medal Lecture here at the European Society of Cataract and Refractive Surgeons meeting, with the title “Will keratectasia be a long-term complication of LASIK?”
“How does ectasia occur?” Dr. Condon asked. “Because the cornea is a membrane, we must remember the membrane theory of elasticity.” Changing the shape and structure of the cornea during refractive surgery may lead to the complication, he said.
“A steepening in the back of the cornea, not the front, may be a reason,” he said.
Mid-peripheral steepening of the cornea results in an immediate reaction and swelling, he said.
Looking at published reports of keratectasia after refractive surgery, Dr. Condon noted that Daniel Z. Reinstein, MD, reported a 0.12% incidence in 5,212 eyes, and Ioannis Pallikaris, MD, reported a 0.66% incidence in 2,873 eyes. According to Market Scope, more than 17 million people worldwide have undergone LASIK, including 8 million in the United States.
Based on the published incidence rates and the number of patients who have undergone LASIK, Dr. Condon noted that there could potentially be 52,800 cases of keratectasia worldwide, but a literature review found only 85 reported cases.
“So what is preventing more cases of ectasia from being reported?” Dr. Condon asked. “Maybe it’s not a short-term problem after all,” he said.
The published literature suggests that biomechanical shifts, topographic changes, higher-order aberrations and flap diameters may all play a role, he said.
“The thickness of the residual stromal bed is a major factor of ectasia,” Dr. Condon said, noting that the current “rule” of leaving a residual stromal bed of 250 µm is actually an evolving principle.
Looking ahead, Dr. Condon said he believes that corneal biometry will help to screen for patients with keratoconus, a generally accepted risk factor for ectasia after refractive surgery.
Presenting data from his own practice, Dr. Condon reviewed 137 eyes that underwent LASIK between 1994 and 2000. The mean patient age was 40 years, mean refractive error was –14.76 D, and mean pupil size was 5.25 mm. Average optical treatment zone was 6 mm.
In planning the LASIK surgery, he said, ideally 30% of total corneal thickness was left as a residual corneal bed. Lasers used to perform LASIK included the Summit Autonomous, Meditec and Technolas.
Postoperatively among these eyes, eight had macular degeneration, 13 had cataracts, eight had decreased night contrast, eight had glare that was not present preoperatively and one had keratoconus.
Twenty percent of the eyes were followed for 8 years, Dr. Condon said.
“Despite our intended undercorrections, at 8 years, 38% were still within 1 D,” he said. The refractive stability over the period was good, he said.
Dr. Condon urged any surgeon who experiences or treats a case of keratectasia following refractive surgery to report it so that a truer incidence and occurrence rate can be calculated.