En-face OCT Research Articles

Trouble de la perfusion artérielle rétinienne et tomographie en cohérence optique-angiographie

To analyze optical coherence tomography angiography (OCT-A) findings in patients with impaired retinal artery perfusion secondary to occlusion of the central retinal artery or its branches, cilioretinal artery occlusion or retinal vein occlusion (RVO). In this retrospective observational study of patients with impaired retinal artery perfusion, we recorded the results of clinical examination and multimodal imaging, including fluorescein angiography, spectral-domain (SD)-OCT, and OCT-A (Optovue) of the central 10degrees with measurement of vascular density. The files of 10patients were analyzed (5men, mean age: 63years), including 3retinal artery occlusions, 4cilioretinal artery occlusions, isolated or combined with central retinal vein occlusion (CRVO), and 3RVO with an arterial component. SD-OCT showed hyper-reflectivity of the inner nuclear layer consistent with paracentral acute middle maculopathy (PAMM) in the acute stage (8eyes) resulting in retinal atrophy as early as the following month. OCT-A revealed capillary dropout in all patients with various degrees, the deep capillary plexus seemed to be more involved than the superficial plexus. A fern-like pattern was observed on en-face OCT in 4eyes, outlining venular contours. Vascular density was significantly diminished (whole en-face density in the deep capillary plexus: 50.39vs. 56.21in the control group, P=0.001). On fluorescein angiography, reperfusion was observed in half of the eyes. OCT-A can be very useful in patients with a transitory arterial occlusion by revealing involvement of the superficial and deep capillary plexus. It may enable a retrospective diagnosis in the case of reperfusion.

Wide-Field En Face Swept-Source Optical Coherence Tomography Features of Extrafoveal Retinoschisis in Highly Myopic Eyes.

To evaluate the features of extrafoveal retinoschisis (EFRS) in highly myopic eyes detected by swept-source optical coherence tomography (SS-OCT). In this retrospective case series, 89 eyes of 65 patients with high myopia and coexisting EFRS were included. The participants underwent a comprehensive ophthalmologic examination, including visual acuity, ocular biometry, refraction, and perimetry. Three-dimensional wide-field scans were obtained with SS-OCT, and en face images were reconstructed with custom software. En face OCT features of EFRS were determined by two ophthalmologists masked to clinical characteristics. The associations of EFRS subtypes with ocular biometry and other OCT changes were evaluated as well. In wide-field SS-OCT scans, EFRS was classified into three different types, the inner limiting membrane (ILM) detachment and inner and outer EFRS, according to the specific layer of the splitting. All these three types were most frequently distributed in the inferotemporal quadrant (71.2% for ILM detachment, 59.5% for inner EFRS, and 75.0% for outer EFRS). Inner limiting membrane detachment and inner EFRS were often adjacent to peripapillary atrophy. Outer EFRS tends to coexist with inner EFRS, as we did not observe any case with standalone outer EFRS or with coexisting with ILM detachment. Eyes with all three types combined had the longest axial length (29.1 ± 1.26 mm, P = 0.003) and the greatest refractive error (-13.0 ± 2.86 diopters [D], P = 0.014). The incidence of retinal microfolds and breaks among subgroups was significantly different (P = 0.012 and 0.003, respectively). Staphyloma was associated with outer EFRS (30.6% with versus 7.6% without outer EFRS). Wide-field SS-OCT reveals the spatial distribution of retinoschisis outside the fovea, and associations with retinal vessels and other retinal landmark structures. Further observations on the longitudinal changes and functional damage would help lead to a better understanding of its mechanism and prognosis.

Gabor fusion master slave optical coherence tomography

This paper describes the application of the Gabor filtering protocol to a Master/Slave (MS) swept source optical coherence tomography (SS)-OCT system at 1300 nm. The MS-OCT system delivers information from selected depths, a property that allows operation similar to that of a time domain OCT system, where dynamic focusing is possible. The Gabor filtering processing following collection of multiple data from different focus positions is different from that utilized by a conventional swept source OCT system using a Fast Fourier transform (FFT) to produce an A-scan. Instead of selecting the bright parts of A-scans for each focus position, to be placed in a final B-scan image (or in a final volume), and discarding the rest, the MS principle can be employed to advantageously deliver signal from the depths within each focus range only. The MS procedure is illustrated on creating volumes of data of constant transversal resolution from a cucumber and from an insect by repeating data acquisition for 4 different focus positions. In addition, advantage is taken from the tolerance to dispersion of the MS principle that allows automatic compensation for dispersion created by layers above the object of interest. By combining the two techniques, Gabor filtering and Master/Slave, a powerful imaging instrument is demonstrated. The master/slave technique allows simultaneous display of three categories of images in one frame: multiple depth en-face OCT images, two cross-sectional OCT images and a confocal like image obtained by averaging the en-face ones. We also demonstrate the superiority of MS-OCT over its FFT based counterpart when used with a Gabor filtering OCT instrument in terms of the speed of assembling the fused volume. For our case, we show that when more than 4 focus positions are required to produce the final volume, MS is faster than the conventional FFT based procedure.

En face and OCT angiography findings in macular retinoschisis

The diagnosis of macular retinoschisis is often complex and demands complementary exams to be confirmed. This is the report of a case of a 27 years old man diagnosed with macular retinoschisis, in which En face OCT and OCT angiography were used to identify and demonstrate the typical patterns of the disease, as well as distinguish them from the findings of cystoid macular edema. En face and OCT angiography findings in macular retinoschisis

Morphological differences between optic disc collaterals and neovascularization on optical coherence tomography angiography.

To study morphological features of optic disc venous collaterals (OVCs) and neovascularization of optic disc (NVD) on optical coherence tomography angiography (OCTA). Patients with OVCs and NVDs secondary to ischemic retinal diseases were prospectively enrolled. Multimodal imaging was performed using color fundus photography, fluorescein angiography (FA), and OCTA. Morphological evaluation of en-face structural OCT, cross-sectional and en-face OCTA was performed. Twenty eyes (20 patients; OVCs: n = 10 and NVD: n = 10) were included. OVCs appeared as small, loopy vessels distinct from surrounding peripapillary capillaries on OCTA in the radial peripapillary capillary frame. NVDs appeared as a mesh of fine caliber, raised vessels best seen in the vitreous slab of OCTA. Flow signals in these vascular alterations correlated well with hyperfluorescence on FA. OCTA provides improved visualization of NVDs and OVCs in ischemic retinal diseases such as diabetic retinopathy and retinal vein occlusions compared to conventional FA.

Optical Coherence Tomography Angiography Analysis of Perfused Peripapillary Capillaries in Primary Open-Angle Glaucoma and Normal-Tension Glaucoma.

To compare perfused peripapillary capillary density in primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), and normal patients using optical coherence tomography angiography (OCT-A). A retrospective review of POAG, NTG, and normal patients imaged with OCT-A was performed. En face OCT angiograms identifying peripapillary vessels were obtained using a spectral-domain OCT system (Avanti RTVue-XR). A custom image analysis approach identified perfused peripapillary capillaries, quantified perfused capillary density (PCD), and generated color-coded PCD maps for 3.5- and 4.5-mm-diameter scans. We compared PCD values, PCD maps, standard automated perimetry (Humphrey visual field [HVF]) parameters, and OCT retinal nerve fiber layer (RNFL) thickness analyses across all groups. Forty POAG, 26 NTG, and 26 normal patients were included. Annular PCD in POAG (34.24 ± 6.76%) and NTG (37.75 ± 3.52%) patients was significantly decreased compared to normal patients (42.99 ± 1.81%) in 4.5-mm scans (P < 0.01 and P < 0.01, respectively). Similar trends and statistical significances were seen in 3.5-mm scans. Linear regression analysis resulted in moderate correlations between annular PCD values and other glaucomatous parameters. Pearson coefficients comparing annular PCD from 4.5-mm scans in POAG and NTG groups to HVF mean deviation, HVF pattern standard deviation, and average RNFL thickness all showed statistical significance (P < 0.05). Color maps showed that POAG and NTG patients had a reduction of perfused capillaries that progressed in size when comparing early, moderate, and severe glaucoma groups. Optical coherence tomography angiography can uniquely identify changes in peripapillary PCD in glaucoma patients. Optical coherence tomography angiography may offer insights into the pathophysiology of glaucomatous damage and risk factors for disease progression.

Evaluation of Nonperfused Retinal Vessels in Ischemic Retinopathy.

Retinal ischemia has been traditionally assessed by fluorescein angiography, visualizing perfused vessels. However, this method does not provide any information about nonperfused vessels, and although it is often assumed that vessels in ischemic areas regress, we know little about how nonperfused retinal vessels change over time. Here, we aim to learn more about the long-term fate of nonperfused vessels in the retinal vasculature. Optical coherence tomography (OCT) was used to visualize perfusion as well as structural properties of the retinal vasculature in patients suffering from retinal vascular occlusions. In addition, postmortem tissue from a patient with long standing (6 years) central retinal vein occlusion (CRVO) was investigated, using immunohistochemistry on whole-mount retina and paraffin sections to visualize blood vessel components. Comparing OCT angiography with enface OCT images revealed that in ischemic areas of the retina, nonperfused, larger vessels could be detected as hyperreflective structures in enface OCT images. Furthermore, analysis of a postmortem tissue sample from a CRVO patient with a large nonperfused region in the macula, revealed preservation of the basement membrane from all retinal vessels, including nonperfused, acellular vessels of all calibers. Our data suggests long-term preservation of vascular basement membrane in ischemic retina. This has implications for therapeutic approaches aiming to alleviate retinal ischemia via the regeneration of damaged vessels.

En face OCT of uncomplicated angioid streaks

PurposeThe Optical Coherence Tomography (OCT) is not a good diagnostic method for uncomplicated angioid streaks. Even the most better resolution imaging forms such as Spectral Domain OCT or Swept Source OCT has no sufficient resolution to distinguish the locations of small splines. The aim of this study is to report the imaging characteristics of uncomplicated angioid streaks using en face Spectral Domain OCT (SD‐OCT).MethodsPatients with uncomplicated angioid streaks were imaged using Spectralis SD‐OCT. A macular cube composed of 248 μm 20° × 15° 19‐line raster scans was obtained. En face SD‐OCT characteristics were evaluated by taking images at the retinal pigment epithelium level taking into account all its thickness.ResultsLarge angioid streaks are visible in en‐face SD‐OCT as a hiporreflective groove structure, representing the pigment epithelium, surrounded by a hiperreflective area that corresponds to its absence.ConclusionsSD‐OCT en face imaging can be used in clinical practice to identify and follow patients with uncomplicated angioid streaks. ‘Follow‐up’ functions of the SD‐OCT may help in the future to better understantd the behavior of these lesions.

Tail artifact removal in OCT angiography images of rodent cortex.

Optical coherence tomography angiography (OCTA) is a surging non-invasive, label-free, in vivo volumetric imaging method, currently being translated to clinical ophthalmology and becoming popular in neuroscience. Despite its attractiveness, there is an inherent issue of using OCT angiograms for quantitative cerebrovascular studies: The dynamic scattering of moving erythrocytes within pial vasculature creates tail-like artifacts that shadow the capillary vessels in the deeper layers of cortex. This false flow effect is relatively benign for qualitative visualization purposes, but it might have a significant impact on quantitative interpretation of angiographic results. In this work, we propose a simple image processing method to remove these tail artifacts in depth-resolved OCTA images using an adaptive enface mask generated with OCT structural images. We demonstrate the effectiveness of our method by comparing vessel densities and vessel similarities of depth-resolved OCT angiograms in a stroke study in a rodent model, in vivo. Thanks to the ability of seeing through the tails of pial vessels, capillary vessels beneath these vessels could be recovered to some extend in the deeper layers of mouse cerebral cortex, leading to a more accurate quantification. Tail artifact removed enface OCT angiogram of deeper layer in vivo mouse cortex.

Relationship between Functional and Structural Changes in Diabetic Vessels in Optical Coherence Tomography Angiography.

The decorrelation signals in optical coherence tomography angiography (OCTA) are derived from the flow of erythrocytes and concomitantly delineate the retinal vasculature. We compared the structural and functional characteristics of vascular lesions visualized in fluorescein angiography (FA), OCTA, and en-face OCT images in 53 eyes (28 patients) with diabetic retinopathy (DR). The foveal avascular zone (FAZ) areas in OCTA images in the superficial layer almost corresponded to those in FA images. The FAZ areas in the en-face OCT images in the superficial layer were smaller than those in the FA images and correlated with each other, which agreed with the finding that en-face OCT images often delineated the vascular structure in the nonperfused areas in FA images. Microaneurysms appeared as fusiform, saccular, or coiled capillaries in OCTA images and ringed, round, or oval hyperreflective lesions in en-face OCT images. OCTA and en-face OCT images detected 41.0 ± 16.1% and 40.1 ± 18.6%, respectively, of microaneurysms in FA images, although both depicted only 13.9 ± 16.4%. The number of microaneurysms in FA images was correlated with that in OCTA and en-face OCT images. Comparisons of these modalities showed the associations and dissociations between blood flow and vascular structures, which improves the understanding of the pathogenesis of DR.

Intraretinal changes in the presence of epiretinal traction.

To determine the correlation between the area of morphological changes on the macular surface, the depth of intraretinal changes and the best-corrected visual acuity (BCVA) in patients with idiopathic epiretinal membrane. In this prospective cross-sectional study, 38 patients underwent BCVA testing with a Snellen eye chart. The depth of traction, photoreceptor outer segment layer (PROS) thickness, central macular thickness (CMT) and presence of intraretinal cysts were measured using the Avanti RTVue XR and 3D Widefield Enface OCT instruments. Enface sections were performed at the inner limiting membrane (ILM) line level (ILM offset). Patients were categorized into two groups: in group 1 (n = 21), the depth of traction was within 90μm from the ILM, and in group 2 (n = 17) it was beyond 90μm from the ILM. The main outcome measure was the correlation between area of epiretinal traction and BCVA according to the depth of traction. In group 1, the depth of traction was 55.15 ± 14.28μm, the area of traction was 38.95 ± 13.63mm2, PROS thickness was 51.20 ± 7.23μm, and CMT was 362.65 ± 41.08μm. In group 2, the depth of traction was 112.24 ± 10.89μm, the area of traction was 25.18 ± 4.07mm2, PROS thickness was 50.24 ± 9.01μm, and mean CMT was 534.29 ± 126.81μm. Statistically significant differences in depth of traction, area of traction and CMT were found between the two groups (P < 0.001). The relationship between structure and function between the area of traction and BCVA was better explained in group 2 (r = 0.814, P < 0.001). We found that intraretinal changes were induced by the ERM, and varied according to the depth of traction measured with en face analysis. In the case of traction deeper than 90μm, we found a significant correlation between the inner area of the epiretinal traction and BCVA. We believe that retinal stress induced by epiretinal traction is better characterized by combining information provided by sagittal and transverse OCT scans, thus defining its prognostic significance in ERM.

En face OCT in Stargardt disease

To evaluate the structural features of the macular region by enface OCT imaging in patients with clinical diagnosis of Stargardt disease, confirmed by the detection of ABCA4 mutations. Thirty-two STGD patients were included in the study for a total of 64 eyes. All patients received a comprehensive ophthalmological examination, color fundus photography, fundus auto-fluorescence imaging and OCT. Five OCT scans were considered: ILM and RPE scans (both automatically obtained from the instrument), above-RPE slab, photoreceptor slab and sub-RPE slab (these last three manually obtained). ILM scans showed evident radial folds on the retinal surface in 8/64 eyes (12.5%). In 6 of the 7 patients, these vitreo-retinal interface abnormalities were unilateral. The photoreceptor slab showed some macular alterations ranging from dis-homogeneous, hypo-reflective abnormalities (7/64 eyes, 11%) to a homogeneous, well-defined, roundish, hypo-reflective area (17/64 eyes, 27%) in all the eyes. The sub-RPE slab showed a centrally evident, hyper-reflective abnormality in 58/64 eyes (90.6%). Superimposing the sub-RPE slab over the images corresponding to the photoreceptor slab, the area of the photoreceptor atrophy sharply exceeded that of the RPE atrophy (44/46 eyes, 96%). Enface OCT proved to be a clinically useful tool for the management of STGD patients, illustrating in vivo the structural abnormalities of the different retinal layers.

En face enhanced depth imaging optical coherence tomography of polypoidal choroidal vasculopathy

PurposeTo analyse retinal and choroidal changes associated with polypoidal choroidal vasculopathy (PCV) using en face spectral-domain optical coherence tomography (SD-OCT).MethodsIn this retrospective and descriptive study, we collected imaging of patients...

ENLARGEMENT OF FOVEAL AVASCULAR ZONE IN DIABETIC EYES EVALUATED BY EN FACE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

To evaluate the area of the foveal avascular zone (FAZ) detected by en face OCTA (AngioVue, Avanti OCT; Optovue) in healthy and diabetic eyes. Retrospective chart review of patients who underwent fundus examination including en face OCTA. Eyes with proliferative diabetic retinopathy and history of laser photocoagulation were excluded. The FAZ area in the superficial and deep plexus layers were measured and evaluated using ImageJ software. The FAZ area in the superficial layer was 0.25 ± 0.06 mm² in healthy eyes (n = 19), whereas it was 0.37 ± 0.07 mm² in diabetic eyes without retinopathy (n = 24) and 0.38 ± 0.11 mm² in eyes with diabetic retinopathy (n = 20). Diabetic eyes showed statistically significant FAZ enlargement compared with healthy eyes, regardless of the presence of retinopathy (P < 0.01). The FAZ area in the deep plexus layer was also significantly larger in diabetic eyes than in healthy eyes (P < 0.01). Our data suggest that diabetic eyes show retinal microcirculation impairment in the macula even before retinopathy develops. En face OCTA is a useful noninvasive screening tool for detecting early microcirculatory disturbance in patients with diabetes.

En Face OCT and OCT‐Angiography in ocular oncology

SummaryEn Face OCT and OCT Angiography are two innovative diagnostic modalities which were adapted for the diagnosis, therapeutic decision and observation of the evolution following conservative management in ocular oncology. En Face OCT is particulary useful for (1) The definition of the extend of serous retinal detachment and the documentation of its variations (2) The definition of the internal anatomical structure of unpigmented choroidal tumors (3) The definition of the limits of flat and diffused choroidal melanomas in order to define the target volume of the irradiation. Angio‐OCT in ocular oncology is mainly used for the definition of retinal vascular lesions observed in radiation induced optic neuropathy and radiation induced maculopathy. This allows a better definition of the therapeutic strategies with anti‐VEGF drugs in order to preserve visual function.

Master slave en-face OCT/SLO.

Master Slave optical coherence tomography (MS-OCT) is an OCT method that does not require resampling of data and can be used to deliver en-face images from several depths simultaneously. As the MS-OCT method requires important computational resources, the number of multiple depth en-face images that can be produced in real-time is limited. Here, we demonstrate progress in taking advantage of the parallel processing feature of the MS-OCT technology. Harnessing the capabilities of graphics processing units (GPU)s, information from 384 depth positions is acquired in one raster with real time display of up to 40 en-face OCT images. These exhibit comparable resolution and sensitivity to the images produced using the conventional Fourier domain based method. The GPU facilitates versatile real time selection of parameters, such as the depth positions of the 40 images out of the set of 384 depth locations, as well as their axial resolution. In each updated displayed frame, in parallel with the 40 en-face OCT images, a scanning laser ophthalmoscopy (SLO) lookalike image is presented together with two B-scan OCT images oriented along rectangular directions. The thickness of the SLO lookalike image is dynamically determined by the choice of number of en-face OCT images displayed in the frame and the choice of differential axial distance between them.

Reflection, phase and en-face sectional imaging of scattering objects using quasi-single-shot wide-field optical coherence tomography

We report a quasi-single-shot wide-field optical coherence tomography system that enables to measure the reflection, phase and en-face OCT images from the same setup using the glass jig. The jig consisting of a wedge glass substrate and a glue dot is contacted to the tissue surfaces, and the data within glue dot is used to reduce the phase noise of the interference signal. The reconstructed image size of the object was 4.0 mm × 4.3 mm. The standard deviation (STD) of the phase variation was minimized by 54 % and obtained to be 0.027 rad for the poke tissue. The corresponding STD in optical path length change was measured to be 1.4 nm. The refractive index of the water and poke tissue at the surface is also evaluated as 1.36 and 1.39, respectively, using reflection intensity images. Further, the en-face sectional images of the tissue sample are also measured.

Feasibility of level-set analysis of enface OCT retinal images in diabetic retinopathy.

Pathology segmentation in retinal images of patients with diabetic retinopathy is important to help better understand disease processes. We propose an automated level-set method with Fourier descriptor-based shape priors. A cost function measures the difference between the current and expected output. We applied our method to enface images generated for seven retinal layers and determined correspondence of pathologies between retinal layers. We compared our method to a distance-regularized level set method and show the advantages of using well-defined shape priors. Results obtained allow us to observe pathologies across multiple layers and to obtain metrics that measure the co-localization of pathologies in different layers.

Improvement of the dynamic range using background subtraction in single shot wide-field optical coherence tomography

We investigated on the signal in single shot wide-field optical coherence tomographic (SS-WF-OCT) system to improve the dynamic range (DR). The SS-WF-OCT system is based on two-dimensional (2D) polarization Michelson interferometer and superluminescent diode (center wavelength of 842.5 nm) as light source. Two π-phase-shifted interferograms were acquired simultaneously using a single CCD camera and after subtraction, the en-face OCT image (area (x) 4.0 mm × (y) 4.3 mm) is obtained using 2D Hilbert transform. The OCT signal including incoherent background noises was analyzed. To improve the DR, background noise subtraction has been introduced and its measurement process is presented. This method is valuable during the background noise is stable. Using the scattering samples, such as, grind metal and polymer sponge with background subtraction algorithm, a significant reduction in background noise and improvement in the DR was demonstrated .

Predictive value of outer retina Enface OCT imaging in geographic atrophy progression

AbstractPurpose To determine wether there was a correlation between hypo reflective area in Enface OCT of outer retina at baseline, and geographic atrophy (GA) area 1 year later in dry age‐related macular degeneration (AMD)Methods Retrospective study. We included all patients who underwent a clinical examination for dry AMD from July to November 2013 and who had macular captured Enface OCT. Eyes with previously treated wet AMD were excluded. We analysed hypo reflectivity on Enface SD‐OCT extraction (Cirrus 2, Carl Zeiss Meditec,Dublin) of the outer retina 20 µm above retinal pigmented epithelium (RPE), corresponding to the disruption of ellipsoid line (EZ), and extraction below RPE corresponding to GA, the speed of progression of these 2 parameters, the pattern of these areas, best corrected visual acuity (BCVA) on ETDRS scale, and foveal involvement in GA. Our endpoint was the correlation between the difference area EZ‐GA and GA enlargement over 1 year on Enface OCT. Our secondary endpoint was the pattern similarities between both of these parameters.Results We included 38 eyes of 31 patients with dry AMD, mean age was 84,9 years. At baseline, mean size of GA area was 7.1 mm2, mean size of hypo reflectivity was 9.28 mm2, fovea was involved in GA in 49% of cases, BCVA was 64.2 letters. One year later, mean size of GA area was 9.2 mm2, fovea was involved in 54% of cases, BCVA was 58.8 letters. The rate of progression of GA was 2.04 mm2 per year. The difference EZ‐GA at baseline and GA enlargement were not strongly correlated. The pattern of EZ disruption on Enface OCT was correlated in more than 2/3rd of cases with the pattern of GA 1 year later.Conclusion EZ disruption and GA 1 year later are not constantly correlated