HEALING CASCADES

Corneal crosslinking (CXL) offers an effective means of halting the progression of keratoconus in the majority of patients, with an excellent safety profile and a low rate of complications, Theo Seiler PhD told delegates attending the 6th EuCornea Congress in Barcelona, Spain. “Five to ten year reports in the scientific literature demonstrate that CXL using 3mW/cm2 has a complication rate ranging from zero to 13 per cent and a failure rate of zero to three per cent. Complications such as scars and infiltrates are rare, and we should remember that the cornea is at its most vulnerable during the re-epithelialisation period of three to five days postoperatively. It should also be borne in mind that CXL induces structural changes in the cornea that may go on for many years after the treatment,” Prof Seiler said. A complication in a surgical procedure in ophthalmology, according to the FDA definition, is defined as a loss of two or more Snellen lines of visual acuity, said Prof Seiler. “If we look at one of the early studies we conducted in 2005 in over 100 eyes, we found a complication rate at one year postoperatively of around three per cent. Further analysis of the data showed two main risk factors to have a complication: age older than 35 and preoperative best corrected visual acuity (BCVA) greater than 20/25,” he said. RECENT EVIDENCE Looking at more recent evidence in the scientific literature, Prof Seiler said that PubMed now lists around 155 publications relating to complications after CXL. Perhaps the highest complication rate of 13.7 per cent comes from a study by Hashemi et al (Ophthalmology 2013;120:1515-1520) in a group of 40 eyes of 32 patients with five years follow-up, while at the other end of the scale O’Brart et al reported a rate of zero per cent for more than 30 eyes with four to six years follow-up (Br J Ophthalmol 2013;97:433-437). “We might well ask what is different in Iran compared to the UK to account for such a difference and it might well be that the postoperative or perioperative hygienic situation is different in each country,” he said. Failure rates, defined as a progression of the keratoconus with a Kmax increase of more than 1.0D in a year, also need to be considered, said Prof Seiler. “We found in our own prospective study carried out in Zurich in 2007 a failure rate at one year postoperatively in more than 100 eyes of three per cent. The only risk factor identified was if the keratoconus was too far advanced at the time of treatment, there was a greater chance of progressions.” Looking at other published studies, one study from France reported a failure rate at one year in more than 100 eyes of 2.8 per cent (Asri et al, JCRS, Vol. 37, Issue 12, 2137-2143), while O’Brart et al’s rate at four years postoperatively in more than 40 eyes was zero per cent. Patient selection perhaps accounted for the difference between the two outcomes, noted Prof Seiler. INTRIGUING CASE He then discussed the intriguing case of a patient who first received CXL treatment in 2005 for his progressive keratoconus and who continued to experience a progressive flattening effect on the cornea over the follow-up period. “In 2006, I was his hero because his eyesight was improving and he needed new glasses, and then in 2009 he was running around without glasses. He came back to the clinic last year and he was wearing glasses again: that flattening effect of crosslinking continued for more than 10 years,” he said. Some other similar cases have also been reported in the literature, said Prof Seiler, who estimates that less than 10 per cent of patients will be affected in this way. “This goes to show that CXL is not just switch-on and switch-off. When we do CXL we are obviously initiating some healing cascades in the cornea that go on for years after the treatment,” he said. Other complications to watch for include stromal haze, sterile infiltrates and late-onset stromal scarring, all of which can usually be treated successfully without loss of vision, concluded Prof Seiler. To contact Theo Seiler, email: claudia.kindler@iroc.ch