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Hessam Roodaki, Niklas Alexander Maierhofer, Anne-Marie Jablonka, Ali Nasseri, Chris Patrick Lohmann, Abouzar Eslami; OCT-based volumetric measurement of subretinal injection blebs in ex-vivo porcine eyes. Invest. Ophthalmol. Vis. Sci. 2020;61(7):472.
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© ARVO (1962-2015); The Authors (2016-present)
Therapeutic approaches involving surgical drug delivery directly above Retinal Pigment Epithelium (RPE) have already found their way into the clinical practice. Subretinal injections require fine control and measurement of parameters such as the injection volume. Although delivery devices report the amount of therapeutics injected into the eye, the amount deposited above the RPE in form of a bleb requires other means of measurement. In this work, intraoperative Optical Coherence Tomography (OCT) is used for volumetric measurement of subretinal blebs.
Freshly enucleated porcine eyes (N=7) were prepared for robot-assisted subretinal injection by fixation to silicone pads and trocar insertion. 40G bent subretinal needles attached to a custom-built 6 degrees of freedom (6DoF) master-slave robot were used for injection. The procedure was performed on all eyes under a Lumera 700 microscope with RESCAN 700 (Zeiss, Oberkochen, Germany) guided by intraoperative OCT. After penetration through retina, an OCT volume covering the area around the tip of the needle was acquired. Then perfluorocarbon heavy liquid was injected using a custom-built delivery device. After the formation of the subretinal bleb, a second OCT volume covering the entire bleb was acquired. The two OCT acquisitions were processed by a combination of geometric correction, RPE segmentation and voxel counting algorithms.
Volumes of 1.60µL or 2.24µL were injected in all experiments. 2 cases where no visual reflux of the injected volume was observed in the microscopic view were selected for measurement. In one case, a volume of 2.13µL was measured compared to the actual injection of 2.24µL (5.2% deviation) and in the other case a volume of 1.41µL was measured compared to the actual injection of 1.60µL (13.5% deviation). The disparity between the measurements and the actual injection amount may be attributed to the invisible reflux of the injected liquid.
Systematic volumetric measurement of subretinal injection blebs is feasible using intraoperative OCT volume captures. Accuracy of such measurements could be determined using phantom models.
This is a 2020 ARVO Annual Meeting abstract.
A) OCT cross-sectional view of a bleb formed above the RPE after injection. B) Segmentation of the same bleb annotated in blue.
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