Journal of Refractive Surgery Volume 21 November/December 2005
Keratoconus and Corneal Ectasia After LASIK
Perry S. Binder, MS, MD; Richard L. Lindstrom, MD; R. Doyle Stulting,
MD, PhD; Eric Donnenfeld, MD; Helen Wu, MD; Peter McDonnell, MD; Yaron
Excerpt: Ectasia is a known risk of laser vision correction, and if ectasia occurs in a patient following laser vision correction it does not necessarily mean that the patient was a poor candidate for surgery, that the surgery was contraindicated, or that there was a violation of the standard of care.
More On Ectasia
Post-LASIK ectasia possible with no known risk factors.
Careful preoperative screening critical; some eyes have no indication of potential problems
Oct 1, 2005
By: Cheryl Guttman
Ectasia can occur after an otherwise uncomplicated LASIK procedure, even in the absence of recognized risk factors, said Shawn R. Klein, MD, at World Cornea Congress V.
"Careful preoperative evaluation to screen out inappropriate candidates is critical for avoiding ectasia post-LASIK, but we also encourage surgeons to consider routinely measuring intraoperative stromal bed pachymetry," said Dr. Klein, clinical instructor, Institute of Ophthalmology and Visual Science, New Jersey Medical School, Newark. "However, even in the eye that appears to have no risk factors, ectasia can occur."
Dr. Klein together with Randy J. Epstein, MD, J. Bradley Randleman, MD, and R. Doyle Stulting, MD, PhD, collected a series of cases of post-LASIK ectasia that developed in the absence of risk factors. Over a 7-month period in 2003, they solicited cases through three Internet news groups.
A total of 27 eyes of 25 patients were submitted from surgeons around the world, and when rigorous criteria were applied to exclude patients with any known possible risk factors for ectasia, nine eyes of eight patients remained in the series. All were treated for low to moderate refractive errors (maximum MRSE, –8 D). Time to onset of ectasia recognition after LASIK ranged from 3 to 27 months.
The risk factor exclusion criteria consisted of: calculated residual stromal bed <250 μm, preoperative central pachymetry <500 μm, any keratometry reading >47.2 D, I - S value >1.4, attempted initial correction > –12 D, Orbscan II posterior float >50 μm (when available), > two re-treatments, and surgical/flap complications.
"We also went back to the literature to find cases of ectasia that met our study criteria and even when limiting our review to eyes with a residual stromal bed >250 μm, it was very difficult to find cases that would satisfy our rigorous exclusion criteria," Dr. Klein said. "Most of the cases in the literature had topographies that we found to be suspicious when evaluated very carefully or were lacking other data that are important for determining risk."
Dr. Klein proposed three hypotheses to account for why patients might develop ectasia despite having no apparent risk factors. One possibility is that the residual stromal bed was inadequate due to creation of an excessively thick flap and/or excessive ablation.
"Intraoperative data from stromal bed pachymetry were only available for one of the nine eyes in our series and so we did not know flap thickness for most of the cases," he noted.
Dr. Klein also proposed that these patients may have had preoperative topographic abnormalities that were undetected because the machines were not sensitive enough or not used correctly. Supporting that possibility is the fact that the submitted scans for some of the patients were of limited detail, making I - S calculations difficult.
According to Dr. Klein, a third possibility is "most tantalizing," and that is that these patients have biomechanically unstable corneas with no preoperative abnormalities detectable using widely available technology.
"I like to think of these cases as a forme fruste keratoconus and that they are unable to withstand the insult of LASIK," Dr. Klein said.
Of interest with respect to that concept, in an analysis of the demographic and operative data for the series of eight cases, age emerged as a potentially remarkable factor for the group. The eight patients in the series were found to be significantly younger than the mean age reported in a previously published series [Randleman, et al. Ophthalmology 2000;110:267-275] for both patients who developed ectasia and control groups.
"Perhaps some of these patients might have eventually developed keratoconus even if they had not undergone LASIK, but the surgery accelerated the onset," Dr. Klein explained. "However, our data suggest that the risk of ectasia in the absence of known risk factors may be higher in younger patients."
Dr. Klein also noted that as one of its limitations, the cases in this retrospective study were contributed by multiple different surgeons who used different techniques and technology, including a number of different microkeratomes, lasers, and pachymeters.