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Review of a small series of eyes shows surface ablation procedures do not eliminate the risk of postoperative ectasia in eyes with forme fruste keratoconus, even in eyes without other ectasia risk factors.
London- Ectasia can develop after surface ablation in eyes with forme fruste keratoconus (FFKC), and no identifiable features appear to protect against that event, according to the findings of a retrospective study.
"Surface ablation is increasingly being performed around the U.S. and other countries partly to avoid flap complications, but also to prevent ectasia," said Sheraz M. Daya, MD, director and consultant, Corneoplastic Unit and Eye Bank, Queen Victoria Hospital, East Grinstead, and medical director, Centre for Sight, London and East Grinstead.
"However, the questions of whether it eliminates or minimizes the risk of that complication and whether it is truly safe in patients with FFKC if they have thick corneas or flat corneas have not been answered," Dr. Daya said.
The review was based on eight eyes of four patients seen on referral for the development of ectasia between April 2002 and June 2005. Seven eyes had frank ectasia, whereas one had progression of FFKC that was not clinically significant as the patient retained good unaided vision. Six eyes had preoperative data available, and all were identified as having FFKC or pellucid-like changes on topography.
The eyes had undergone myopic LASEK or PRK, and the mean time to presentation afterward was 32 months. One case developed after 9 years, but all others occurred within the first 4 to 9 months.
"With the exception of the late-onset case, we do not think these eyes would have developed ectasia anyway even if they did not have refractive surgery," Dr. Daya said.
The features of the patients in the series provided the basis for the conclusions that a thick cornea, flat cornea, and age over 40 years probably do not reduce the risk of ectasia after surface ablation in eyes with FFKC. At the time of the refractive surgery, the patients had a mean age of 34 years; two were aged more than 40 years. Preoperative corneal thickness averaged 519 μm and exceeded 500 μm in five of the six eyes.
Preoperative keratometry averaged 45.1 D, with a minimum K reading of 42.75/43.00 D. Mean preoperative spherical equivalent (SE) was about –4.0 D, and mean tissue ablation depth was 100 μm with a range of 25 to 167 μm.
Upon presentation to Dr. Daya's center, the eyes had a mean SE of –1.6 D and more astigmatism than prior to their refractive surgery as measured by both refraction and keratometry. The mean K value was 44 D and mean corneal thickness was 461 μm.