BACKGROUND AND OBJECTIVE: Optical coherence tomography angiography (OCTA) is a novel, non-invasive OCT technique capable of imaging the retinal vasculature. This study aims to evaluate the retinal microvasculature in diabetic human subjects with OCTA and assess potential clinical applications. PATIENTS AND METHODS: Cross-sectional study of 33 subjects with diabetic retinopathy. OCTA was performed on 3 mm × 3 mm sections using a swept-source OCTA prototype and a phase- and intensity-based contrasting algorithm. OCT angiograms were studied with corresponding clinical examination and fluorescein angiograms, when available, to assess accuracy and clinical utility. RESULTS: OCTA was able to demonstrate most clinically relevant vascular changes in subjects with diabetic retinopathy, including microaneurysms, impaired vascular perfusion, some forms of intraretinal fluid, vascular loops, intraretinal microvascular abnormalities, neovascularization, and cotton-wool spots that were largely consistent with fluorescein angiography. CONCLUSION: OCTA generates high-resolution angiograms that illustrate many of the clinically relevant findings in diabetic retinopathy and offers a novel complement or alternative to fluorescein angiography. Although currently an investigational technique, OCTA in combination with standard OCT imaging is at least as good as fluorescein angiography in the evaluation of the macular complications of diabetic retinopathy. [ Ophthalmic Surg Lasers Imaging Retina. 2015;46:796–805.]

High-frequency needle ultrasound transducers with an aperture size of 0.4 mm were fabricated using lead magnesium niobate-lead titanate (PMN-33%PT) as the active piezoelectric material. The active element was bonded to a conductive silver particle matching layer and a conductive epoxy backing through direct contact curing. An outer matching layer of parylene was formed by vapor deposition. The active element was housed within a polyimide tube and a 20-gauge needle housing. The magnitude and phase of the electrical impedance of the transducer were 47 Omega and -38deg, respectively. The measured center frequency and -6 dB fractional bandwidth of the PMN-PT needle transducer were 44 MHz and 45%, respectively. The two-way insertion loss was approximately 15 dB. In vivo high-frequency, pulsed-wave Doppler patterns of blood flow in the posterior portion and in vitro ultrasonic backscatter microscope (UBM) images of the rabbit eye were obtained with the 44-MHz needle transducer

To quantitatively evaluate the retinal microvasculature in human subjects with retinal venous occlusions (RVO) using optical coherence tomography angiography (OCTA). Retrospective, cross-sectional, observational case series. Sixty subjects (84 eyes) were included (20 BRVO, 14 CRVO, 24 unaffected fellow eyes, and 26 controls). OCTA was performed on a prototype, spectral domain-OCTA system in the 3x3mm central macular region. Custom software was used to quantify morphology and density of retinal capillaries using four quantitative parameters. The vasculature of the segmented retinal layers and nonsegmented whole retina were analyzed. Fractal dimension (FD), vessel density (VD), skeletal density (SD), and vessel diameter index (VDI) within the segmented retinal layers and nonsegmented whole retina vasculature. Nonsegmented analysis of RVO eyes demonstrated significantly lower FD (1.64±0.01 vs 1.715±0.002; p<0.001), VD (0.32±0.01 vs 0.432±0.002; p<0.001), and SD (0.073±0.004 vs 0.099±0.001; p<0.001) compared to controls. Compared to the fellow eye, FD, VD and SD were lower (p<0.001), and VDI was higher (p<0.001). FD, VD, and SD progressively decreased as the extent (or type) of RVO increased (control vs BRVO vs CRVO; p<0.001). In the unaffected fellow eye FD, VD and SD showed significant differences when compared to control eyes or affected RVO eyes (p<0.001). Quantitative OCTA of the central 3x3mm macular region demonstrates significant differences in capillary density and morphology among subjects with BRVO and CRVO compared to controls or unaffected fellow eyes in all vascular layers. The unaffected fellow eyes also demonstrate significant differences when compared to controls. OCTA allows for noninvasive, layer-specific, quantitative evaluation of RVO-associated microvascular changes.

Purpose. To evaluate the effects of intravitreous bevacizumab in a rabbit retinal neovascularization model. methods. Twenty-four rabbits were divided into five groups. Group A included four rabbits; all other groups included five rabbits each. Group A received intravitreous VEGF only, and group E received intravitreous bevacizumab only. In groups B, C, and D, bevacizumab was injected at the same time, at day 2 and at week 1 after VEGF injection, respectively. Follow-up evaluations continued for 3 weeks and included color fundus photography, fluorescein angiography (FA), and optical coherence tomography (OCT). Enucleated eyes were processed for hematoxylin and eosin (H&E) staining. results. Intravitreous VEGF was associated with disc hyperemia, vascular dilatation and tortuosity, and fluorescein leakage at the disc and in the anterior chamber (AC) at day 2 and with formation of retinal neovascular membranes (NVM) by week 1. At weeks 2 and 3, the NVM was replaced by a fibrotic membrane and mild to moderate capillary nonperfusion. In groups B and C, injection of bevacizumab was very effective in preventing or stopping fluorescein leakage but was not able to prevent or reverse vascular dilatation and tortuosity completely. In group D, bevacizumab injection resulted in severe capillary nonperfusion at week 2. conclusions. Intravitreous injection of VEGF in rabbits results in florid retinal neovascularization within the first week, followed by closure of normal capillaries by week 2. Early intravitreous injection of bevacizumab can prevent these effects, whereas late injection may be associated with more significant closure of normal capillaries. A sudden drop in effective VEGF concentration may be responsible for the closure of the normal capillaries.