Paradigm shift

Intraoperative OCT (RESCAN 700): Microscopic view (left) and simultaneous ‘real-time’ SD-OCT colour image (right). Patient with
full-thickness macular hole (FTMH) during peeling of the ILM Evidence continues to accumulate supporting the usefulness of intraoperative optical coherence tomography (iOCT) in the surgical treatment of a range of vitreoretinal pathologies, according to Prof Mathias Maier, Augenklinik, Klinikum rechts der Isar, Technical University of Munich, Germany. “Probably we are just at the time of the paradigm shift, whereas in five years from now iOCT might be standard in vitreoretinal surgery,” he said. He noted that the integration of non-contact indirect ophthalmoscopy into the surgical microscope was an important advance when first introduced 30 years ago. The technology provides wide field viewing at a high magnification. However, it limits the surgeon to an en face view, whereas retinal surgery requires precise 3D manipulation of delicate tissues at a sub-millimetre scale. AVOIDING DAMAGE Intraoperative OCT with the 
RESCAN 700 (Zeiss) enables that possibility. It provides real-time simultaneous en face surgical microscopy and spectral-domain OCT (SD-OCT) visualisation of the region of interest through the eyepiece. It therefore allows the surgeon to view intraoperatively the impact of their manoeuvres and manipulations, potentially avoiding damage to the retina. When first introduced, iOCT was met with some scepticism from retinal specialists. For example, at the AAO meeting in 2014, only around half of the retinal surgeons polled believed the new technology would come into standard use. But since that time evidence has accumulated to suggest that iOCT is genuinely helpful in procedures such as epiretinal membrane (ERM) and inner limiting membrane (ILM) peeling and has real potential to improve patients’ outcomes. For example, in a study by Susanne Binder MD and her associates in Vienna, Austria, iOCT ERM peeling was possible in 28 (40%) of 70 eyes without using dyes, and they found no residual membrane even if they re-stained in 94.3%. It also showed that iOCT facilitated decision-making on the need for an intraocular tamponade after membrane peeling and it was comparable to the use of dye in confirming success after membrane peeling and visualisation of flat membranes after staining. (Falkner-Radler et al, Retina 2015;35:2100-2106) Studies by Justis P Ehlers MD and associates have produced similar outcomes. For example, in the PIONEER study, which involved 750 eyes, iOCT altered surgical decisions in 15% of membrane peeling procedures and the recurrence rate for membranes was less than 1%. (Ehlers et al, Invest Opththalmol Vis Sci 2014;56:1141-1146) In addition, in the DISCOVER study, which involved 350 eyes, iOCT revealed the presence of residual membranes requiring additional peeling that were not visible with standard surgical microscopy in 16% of cases. (Ehlers et al, JAMA Opthalmol 2015; 133 :124-1132 ) Prof Maier noted that his own experience with 17 patients treated for full-thickness macular holes using iOCT supports the findings of the published studies. The technology provided higher magnification of the gap between the ERM and the retina at the initiation of peeling as well as the ILM during and after peeling. In addition, iOCT enables visualisation of retinal deformation during peeling, which in some cases led the surgeons to alter their peeling approach. The intraoperative feedback was also very helpful when using ILM-peeling with the inverted ILM flap technique. FOVEAL CONTOUR Furthermore, the clear visualisation 
of the foveal contour and cystic roof could help spare the fovea during peeling. Also very helpful is the visualisation of retinal detachment, Prof Maier noted. Moreover, iOCT is extremely useful in dense vitreous haemorrhage, when prior to surgery SD-OCT diagnostic is not feasible. However, iOCT is not without its shortcomings, Prof Maier said. At present it provides no tracking of the region of interest, and the shadow of the metallic instruments can be a problem. In addition, surgery times increased a little (30 seconds approximately) and it is also expensive. Future developments will hopefully address many of these problems. “As time goes on since 2014, iOCT is more frequently used and in future, possibly together with heads-up surgery and probably robotic microsurgery, this trend is going to continue, like computers did starting from the 1980s 
to today,” he concluded. Mathias Maier: mathias.maier@mri.tum.de

Tags: oct, retina