Useful OCT guidance in lamellar corneal procedures

  Intraoperative optical coherence tomography (iOCT) provides very useful but not indispensable guidance in the majority of lamellar corneal procedures, according to a study presented at the 2016 French Implant and Refractive Surgery Association annual meeting in Paris. “While OCT is certainly a useful tool to have for lamellar surgery, it is not absolutely vital in the majority of cases. Its utility varies according to the type of procedure being employed. Our study showed that it was very useful in Descemet’s membrane endothelial keratoplasty (DMEK), moderately useful in deep anterior lamellar keratoplasty (DALK), and less useful in Descemet’s stripping automated endothelial keratoplasty (DSAEK) procedures,” said Eric Gabison MD, PhD. However, OCT is particularly helpful when performing modified intrastromal lamellar sclero-keratoplasty for cases such as advanced pellucid marginal degeneration, he added. The technique was conceived based on iOCT technology. (Guindolet D, Petrovic A, Doan S, Cochereau I, Gabison EE. Sclerocorneal Intrastromal Lamellar Keratoplasty for Pellucid Marginal Degeneration. Cornea. 2016 Jun;35(6):900-3) Prof Gabison tested the real-time iOCT device (RESCAN 700 OCT, Carl Zeiss Meditec) in a variety of corneal lamellar procedures. The OCT is fully integrated into the OPMI LUMERA 700 microscope, with key functions controlled from the microscope’s foot pedal, enabling the surgeon to take videos and 3D OCT images without looking up or stopping the surgery. STROMAL WHITENING In 20 DALK cases, no difference was seen in terms of “big bubble” achievement, however the visibility of the needle or cannula with OCT was safer and more reproducible, particularly for thin corneas. The visibility of the “big bubble” was also the same in routine cases, although OCT did prove useful in rare cases of stromal whitening, said Prof Gabison, Professor of Ophthalmology, Hôpital Bichat and Fondation Ophtalmologique Adolphe de Rothschild, Paris, France. In 10 DSAEK cases, there was no clear advantage using OCT to verify the graft orientation or the position of the cannula before air injection, said Prof Gabison. The device was, however, more useful in the 50 DMEK cases in order to determine the graft orientation before air injection, especially in the case of severe stromal oedema. For challenging cases of corneal disease where sclerocorneal intrastromal lamellar keratoplasty (“SILK”) might be indicated, the OCT proved indispensable for stromal lamellar dissection to correct both corneal thinning and induced corneal astigmatism, said Prof Gabison. (Guindolet D et al. Sclerocorneal Intrastromal Lamellar Keratoplasty for Pellucid Marginal Degeneration. Cornea. 2016 Jun;35(6):900-3; Guindolet D, Gabison EE. AAO 2016, Chicago) In this approach, corneal thinning was first mapped using OCT and then an intrastromal pocket was created by stromal lamellar dissection under OCT guidance. A 300μm-thick stromal lamellar graft was then inserted in the intrastromal pocket before closing the sclera to increase vertical median keratometry. Eric Gabison: egabison@for.paris