Abstract:We compared the performance of three OCT angiography (OCTA) methods: speckle variance, amplitude decorrelation and phase variance for imaging of the human retina and choroid. Two averaging methods, split spectrum and volume averaging, were compared to assess the quality of the OCTA vascular images. All data were acquired using a swept-source OCT system at 1040 nm central wavelength, operating at 100,000 A-scans/s. We performed a quantitative comparison using a contrast-to-noise (CNR) metric to assess the capability of the three methods to visualize the choriocapillaris layer. For evaluation of the static tissue noise suppression in OCTA images we proposed to calculate CNR between the photoreceptor/RPE complex and the choriocapillaris layer. Finally, we demonstrated that implementation of intensity-based OCT imaging and OCT angiography methods allows for visualization of retinal and choroidal vascular layers known from anatomic studies in retinal preparations. OCT projection imaging of data flattened to selected retinal layers was implemented to visualize retinal and choroidal vasculature. User guided vessel tracing was applied to segment the retinal vasculature. The results were visualized in a form of a skeletonized 3D model. Eye (Lond.) 4(2), 262-272 (1990). 4. B. Braaf, K. A. Vermeer, K. V. Vienola, and J. F. de Boer, "Angiography of the retina and the choroid with phase-resolved OCT using interval-optimized backstitched B-scans," Opt. Express 20(18), 20516-20534 (2012 "Real-time speckle variance swept-source optical coherence tomography using a graphics processing unit," Biomed. Opt. Express 3(7), 1557-1564 (2012 Garstecki, and M. Wojtkowski, "Differentiation of morphotic elements in human blood using optical coherence tomography and a microfluidic setup," Opt. Express 23(21), 27724-27738 (2015). 76. W. S. Rasband, "ImageJ," (U. S. National Institutes of Health, Bethesda, Maryland, USA, 1997USA, -2015

Purpose To image retinal macrophages at the vitreoretinal interface in the living human retina using a clinical optical coherence tomography (OCT) device. Methods Eighteen healthy controls and three patients with retinopathies were imaged using a clinical spectral-domain OCT. In controls, 10 sequential scans were collected at three different locations: (1) ∼9 degrees temporal to the fovea, (2) the macula, and (3) the optic nerve head (ONH). Intervisit repeatability was evaluated by imaging the temporal retina twice on the same day and 3 days later. Only 10 scans at the temporal retina were obtained from each patient. A 3-µm OCT reflectance (OCT-R) slab located above the inner limiting membrane (ILM) surface was averaged. Results In controls, ramified macrophage-like cells with regular spatial separation were visualized in the temporal and ONH OCT-R images; however, cell structures were not resolvable at the macula. Interim changes in cell position suggestive of cell translocation were observed between images collected on the same day and those collected 3 days later. There was considerable variation in cell density and nearest-neighbor distance (NND) across controls. Mean ± SD cell densities measured at the temporal and ONH were 78 ± 23 cells/mm 2 and 57 ± 16 cells/mm 2 , respectively. Similarly, mean ± SD NNDs measured at the temporal and ONH were 74.3 ± 13.3 µm and 93.3 ± 20.0 µm, respectively. Nonuniform spatial distribution and altered morphology of the cells were identified in patients with retinopathies. Conclusions Our findings showed regular spatial separation and ramified morphology of macrophage-like cells on the ILM surface with cell translocation over time in controls. Their distribution and morphology suggest an origin of macrophage-like cells such as microglia or hyalocytes.

Purpose We have recently developed a high-resolution microscope-integrated spectral domain optical coherence tomography (MIOCT) device designed to enable OCT acquisition simultaneous with surgical maneuvers. The purpose of this report is to describe translation of this device from preclinical testing into human intraoperative imaging. Methods Prior to human imaging, surgical conditions were fully simulated for extensive preclinical MIOCT evaluation in a custom model eye system. MIOCT images were then acquired in normal human volunteers and during vitreoretinal surgery in patients who consented to participate in a prospective Institutional Review Board-approved study. MIOCT images were obtained before and at pauses in surgical maneuvers and were compared based on pre-determined diagnostic criteria to images obtained with a high-resolution research handheld spectral domain OCT system (HHOCT, Bioptigen Inc., Research Triangle Park, NC) at the same time point. Cohorts of five consecutive patients were imaged. Successful endpoints were pre-defined, including ≥80% correlation in identification of pathology between MIOCT and HHOCT in ≥80% of patients. Results MIOCT was favorably evaluated by study surgeons and scrub nurses, all of whom responded that they would consider participating in human intraoperative imaging trials. The preclinical evaluation identified significant improvements that were made prior to MIOCT use during human surgery. The MIOCT transition into clinical human research was smooth. MIOCT imaging in normal human volunteers demonstrated high-resolution comparable to tabletop scanners. In the operating room, after an initial learning curve, surgeons successfully acquired human macular MIOCT images before and after surgical maneuvers. MIOCT imaging confirmed preoperative diagnoses, such as full-thickness macular hole and vitreomacular traction, and demonstrated post-surgical changes in retinal morphology. Two cohorts of five patients were imaged. In the second cohort, the predefined endpoints were exceeded with ≥80% correlation between MMOCT and HHOCT imaging in 100% of patients. Conclusion This report describes high-resolution MIOCT imaging using our prototype device in human eyes during vitreoretinal surgery, with successful achievement of pre-defined endpoints for imaging. Further refinements and investigations will be directed towards fully integrating MIOCT with vitreoretinal and other ocular surgery to image surgical maneuvers in real time.

PurposeOptical coherence tomography's (OCT) third outer retinal band has been attributed to the zone of interdigitation between RPE cells and cone outer segments. The purpose of this paper is to investigate the structure of this band with adaptive optics (AO)-OCT.MethodsUsing AO-OCT, images were obtained from two subjects. Axial structure was characterized by measuring band 3 thickness and separation between bands 2 and 3 in segmented cones. Lateral structure was characterized by correlation of band 3 with band 2 and comparison of their power spectra. Band thickness and separation were also measured in a clinical OCT image of one subject.ResultsBand 3 thickness ranged from 4.3 to 6.4 μm. Band 2 correlations ranged between 0.35 and 0.41 and power spectra of both bands confirmed peak frequencies that agree with histologic density measurements. In clinical images, band 3 thickness was between 14 and 19 μm. Measurements of AO-OCT of interband distance were lower than our corresponding clinical OCT measurements.ConclusionsBand 3 originates from a structure with axial extent similar to a single surface. Correlation with band 2 suggests an origin within the cone photoreceptor. These two observations indicate that band 3 corresponds predominantly to cone outer segment tips (COST). Conventional OCT may overestimate both the thickness of band 3 and outer segment length.

Optical coherence tomography (OCT) has transformed diagnostic ophthalmic imaging but until recently has been limited to the clinic setting. The development of spectral-domain OCT (SD-OCT), with its improved speed and resolution, along with the development of a handheld OCT scanner, enabled portable imaging of patients unable to sit in a conventional tabletop scanner. This handheld SD-OCT unit has proven useful in examinations under anesthesia and, more recently, in intraoperative imaging of preoperative and postoperative manipulations. Recently, several groups have pioneered the development of novel OCT modalities, such as microscope-mounted OCT systems. Although still immature, the development of these systems is directed toward real-time imaging of surgical maneuvers in the intraoperative setting. This article reviews intraoperative imaging of the posterior and anterior segment using the handheld SD-OCT and recent advances toward real-time microscope-mounted intrasurgical imaging.