2.5 Intraoperative OCT

Over the past decade, optical coherence tomography (OCT) has evolved from a diagnostic imaging modality used exclusively in the clinic to a tool that can be utilized in the operating room.[1] Intraoperative OCT (iOCT) allows the vitreoretinal surgeon to visualize detailed retinal anatomy during surgery beyond the limited en-face view of the retina provided by standard ophthalmic microscopes.[2] The iOCT systems that are currently available create 2D B-scan images in real-time that are useful for visualization immediately before and after surgical manoeuvres.[3] Future developments in swept-source 4D microscope-integrated OCT (MIOCT) may provide a real-time 3D view of retinal structures that facilitate more advanced manoeuvres.[4,5]

The vitreoretinal surgical trainee can effectively utilize the iOCT by following these steps:

Patients requiring procedures with premacular or submacular manipulation may be good candidates for iOCT use.[6] iOCT allows the surgeon to visualize structural changes in the retina after a surgical manoeuvre that may otherwise be invisible with the en-face viewii. For example, the iOCT can confirm that a membrane has been successfully been peeled, an iatrogenic macular hole has not been created, or that subretinal fluid has been adequately drained. It can also confirm that an instrument is in the desired location prior to performing a surgical technique, e.g. accessing the subretinal space for drug delivery (Figure 2.5.1). Vitreoretinal trainees may find iOCT to be useful when performing the following techniques.[7,8,9,10,11]

A hand-held 2D OCT system is now commercially available as the Envisu C-Class (Leica Microsystems).[12] The device is particularly useful in non-sterile cases such as examinations under anaesthesia in young children or other patients who cannot undergo OCT imaging in a clinic setting.[8] It can also be used during vitreoretinal surgery under sterile conditions; however, it requires a pause in the surgery, removal of the microscope, and placement of a sterile bag over the imaging handpiece.[3] Despite these limitations, hand-held OCT can be useful when microscope-integrated OCT is not readily available.

With MIOCT, a live OCT B-scan and crosshairs are generated within the oculars of the operating microscope and on the screen of the microscope console. It can also be used in conjunction with a 3D heads-up display system such as NGENUITY (Alcon), where the OCT image may cause less of a crowding effect when displayed on a large screen.[13] MIOCT is useful for visualizing retinal structures quickly and efficiently either during a surgical manoeuvre or after it has been performed.[3] Commercially available systems include the Rescan 700 (Zeiss) and the EnFocus (Leica).