5.1 Diagnostic/Technology Overview
Intraoperative optical coherence tomography (OCT) allows the surgeon to view the surgical field from a different perspective than a standard ophthalmic microscope. Intraoperative OCT offers excellent resolution for vitreoretinal tissue structure and its alterations during vitreoretinal surgery (▶ Fig. 5.1). This added information significantly impacts surgical decision-making, may improve surgical efficiency, and help to reduce complications. Current commercial systems utilize spectral domain OCT technology within approximate wavelength of 840 to 860 nm, maximum axial resolution of 4 mm, and scanning speed up to 32,000-A scans per second. The microscope-integrated intraoperative OCT platform provides unique opportunities to visualize tissue–instrument interactions during vitreoretinal surgery with real-time surgeon feedback. In the commercial models, the OCT scanner is either fully integrated with the microscope (e.g., RESCAN 700; Zeiss), is attached to the microscope utilizing a camera port (e.g., iOCT; Haag-Streit), or is placed between the objective lens and microscope head (e.g., EnFocus system; Leica).
Fig. 5.1 Normal macula image with intraoperative optical coherence tomography. The scan location and extent of the horizontal and vertical B-scans are shown in blue and pink line on the surgical field.
Another intraoperative OCT platform, the handheld or microscope-mounted portable spectral domain OCT (e.g., Envisu; Leica) allows manual tilting of the OCT scanner head and provides versatile usage in both the operating room and office, but does not have the advantages of a microscope-integrated system.
5.2 Key Applications
5.2.1 Membrane Peeling
Particularly useful during membrane peeling procedures to define the extent of membrane peeling, determine the edge of the membrane, and confirm completion of the membrane peeling (▶ Fig. 5.2).
Fig. 5.2 Intraoperative optical coherence tomography of an epiretinal membrane. The extent of membrane peeling is clearly visualized on both horizontal and vertical B-scan, and the edge of the internal limiting membrane is observed (arrow).
5.2.2 Interface Abnormalities
Excellent for assessing the vitreoretinal interface abnormalities in various diseases including macular holes, epiretinal membrane, vitreomacular traction syndrome, proliferative diabetic retinopathy, proliferative vitreoretinopathy, myopic traction maculopathy, and pediatric vitreoretinopathies. Intraoperative OCT helps to identify posterior vitreous membrane causing vitreoretinal tractional force, locate residual membranes, understand the structure of fibrous/fibrovascular membrane complex, and verify the attainment of surgical goals (▶ Fig. 5.3).
Fig. 5.3 Intraoperative optical coherence tomography of proliferative diabetic retinopathy. Cross-sectional scans visualize the cleavage plane between the fibrovascular tissue and the sensory retina. Vertical B-scan identifies the location of the epicenter (arrow) nasal to the optic disc and the presence of subretinal fluid (arrowhead).
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