KERATOCONUS

Corneal surgeons might agree that by flattening and regularising the cornea, intrastromal corneal ring segment/intracorneal continuous ring (ICRS/ICCR) implantation is a useful method for visual rehabilitation in eyes with keratoconus. However, there is no consensus of opinion about the benefit of this technique for arresting keratoconus progression. At the Expert Meeting on the Surgical Management of Keratoconus, Michael Assouline MD, PhD and Albert Daxer MD, PhD presented data showing disease stabilisation in eyes followed for periods of two to five years after ICCR/ ICRS implantation. However, evidence reported by Alfredo Vega-Estrada MD, MSc, showed only an early, temporary benefit. The meeting took place at the 4th EuCornea Conference in Amsterdam, The Netherlands.

To address the question of whether there is significant progression of keratoconus following ICRS implantation without corneal collagen crosslinking (CXL), Dr Assouline analysed outcomes after two to four years of follow-up in 56 patients who underwent ICRS implantation [Keraring (Mediphacos) or Intacs (Addition Technology)] into femtosecond laser-created channels. Patients were included in the study only if they had to have at least two postoperative topography exams (Orbscan, Bausch + Lomb) performed at least two years apart. Progression was determined based on the differential numerical analysis of the Orbscan data recorder export files (rather than simple comparison of values from printed maps). Absolute changes in anterior axial curvature (Kmax, mean K) and elevation (Anterior elevation and best fit sphere) were plotted against time. Eyes with post-LASIK ectasia or that had CXL, contact lens wear within eight days prior to diagnostic imaging, or severe keratoconus (max K >68 D or minimum pachymetry <400 microns) were excluded.

The results showed a tendency for progressive flattening over time and with the benefit still not reaching a plateau at four years. Dr Assouline acknowledged that the data he presented are not from a rigorously designed study. However, he noted that he has performed ICRS implantation alone in a total of 193 patients, of which none have subsequently undergone CXL.

“It would be useful to establish a patient registry to collect data so that we could better understand the possible benefits of ICRS implantation for stabilising corneal shape,” said Dr Assouline, private practice, Centre Iena Vision, Paris, France.

“However, based on years of follow-up in a reasonable number of cases, I currently don’t see a need to routinely perform CXL with ICRS. In my opinion, there is no obvious benefit for routine CXL that would outweigh its risks, which include infection and potentially blinding corneal ulcers,” said Dr Assouline.

Dr Daxer, private practice, Gutsehen Eye Centre, Linz, Austria, and associate professor of ophthalmology, Medical University Innsbruck, Austria reported on follow-up to five years in a series of 10 eyes implanted with the Myoring (MTP Medical) into a corneal pocket. He explained that when he first began using the Myoring in 2007, he performed CXL simultaneously in eyes with more advanced KCN. However, in 2008, he switched to Myoring implantation only as his initial procedure because the device became available in a broader range of dimensions and reasoning that if progression occurred, he could use the existing corneal pocket for riboflavin injection, allowing for an easy, safer and more comfortable CXL procedure.

Preoperatively, the 10 eyes in his series had an average simK of 52 D and average logMAR UDVA of 1.3. After five years, mean UDVA had improved 9.2 (or 8.4) lines, mean simK had improved 5.5 D (or 5.3), and corneal pachymetry was essentially unchanged. Two of the 10 eyes showed some progression based on simK and pachymetry values, but the changes were only about 1.0 to 2.0 D in mean simK and 20 microns in thickness. Dr Daxer acknowledged the need for a larger series to confirm his results, but he also proposed a mechanism of action to explain how ring implantation can halt keratoconus progression.

Dr Vega-Estrada, Vissum Institute of Ophthalmology of Alicante, Alicante, Spain, noted there are some papers in the literature, including one from his centre [J Cataract Refract Surg. 2013;39(8):1234-40] showing no progression of keratoconus post-ICRS implantation. However, he suggested these reports represent analyses of cases specifically selected because they had stable disease. The study he presented at the Expert Meeting looked at young patients with progressive disease defined by an increase in mean K or steep K ≥0.75 D, increase in cylinder and sphere ≥1 D, and CDVA loss ≥1 line over six months that was confirmed at two visits. Analyses of data from 18 consecutive eyes of 15 patients (ages 19 to 30) showed initial improvement in refractive and topographic status six months after ICRS implantation. However, the benefits regressed during follow-up to five years.

Dr Vega-Estrada also noted that the study has some limitations as the small size of the sample under investigation and a heterogeneous cohort with different degrees of keratoconus. For this reason, conclusions of the present work should be taken with caution. “However, the data suggest that at least in young patients with evolving keratoconus, ICRS implantation may not alter the progressive nature of the disease,” he said.