Purpose:
To explore the optical properties of indocyanine green (ICG) as an optical coherence tomography (OCT) contrast agent during vitreoretinal surgery with intraoperative OCT (iOCT).
Methods:
A retrospective consecutive case series identified 8 eyes undergoing vitreoretinal surgery for epiretinal membrane and/or full-thickness macular hole with iOCT scanning following ICG staining. Pre-stain and post-peel iOCT images were obtained with a microscope-mounted spectral domain OCT device. Qualititative and quantative analysis was performed of the reflectivity changes noted on OCT scans. Pre- and post-stain images were compared for contrast properties at the level of the ILM. Quantitative analysis was performed with ImageJ software. Using a standardized area of measurement, a series of images for each eye was evaluated. Measurements were taken at the numerous anatomic levels, including the ILM and the nerve fiber layer. An OCT contrast ratio was calculated by dividing the mean intensity of the ILM layer by the mean intensity of the NFL layer. This measurement was made for both pre- and post-contrast eyes.
Results:
All 8 eyes had pre and post-ICG iOCT scans performed. ICG staining resulted in prominent increased hyperreflectivity at the level of the ILM on iOCT. Increased shadowing was noted under the area of ICG staining. Increased contrast enhancement was noted centrally in the parafoveal area. A minimum of five scans per eye were available for quantitative analysis of both pre- and post-ICG staining. The mean OCT contrast ratio following ICG staining was 1.42 compared with a mean pre-ICG ratio of 0.98 (p< 0.001) representing a significant increase in relative brightness of the ILM layer.
Conclusions:
ICG provides significant contrast enhancement during iOCT by qualitative and quantitative measures.
Keywords: imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • image processing