Split-spectrum Amplitude-decorrelation Angiography Algorithm Research Articles

Effect of Photodynamic Therapy on Optical Coherence Tomography Angiography in Eyes with Chronic Central Serous Chorioretinopathy

Purpose: To analyze the use of optical coherence tomography angiography (OCTA) in order to observe the changes in chronic central serous chorioretinopathy (CCSC) after half-dose photodynamic therapy (PDT). Methods: This is a retrospective study evaluating an imaging technique in a cohort of patients. Fundus photography, fluorescein angiography (FA), indocyanine green angiography (ICGA) (Heidelberg Spectralis, Heidelberg, Germany), OCT, and OCTA with the split-spectrum amplitude-decorrelation angiography algorithm (XR Optovue, Fremont, CA, USA) were performed prior to half-dose PDT. OCT and OCTA were conducted at week 1, month 1, month 2, and month 3 after half-dose PDT. Results: A total of 33 eyes of 28 patients were enrolled in the study. At the baseline assessment, the patient pool had a mean best-correct visual acuity of logMAR 0.29 ± 0.34 and the mean choroidal thickness was 407.45 ± 77.98 µm. At month 3 after PDT, the patient pool had a mean best-correct visual acuity of logMAR 0.1 ± 0.17 and the mean choroidal thickness was 355.48 ± 67.90 µm. Abnormal flow in the choriocapillary, which corresponded to the initial examinations using OCTA, was observed in all 33 eyes (100%). The images show an irregular high pixel values interval from low pixel values. At week 1 after half-dose PDT, 25 eyes (75.8%) resembled the baseline images of the choriocapillary layer of OCTA. Areas of nonperfusion in the choriocapillary were observed in 5 eyes (15.2%), and vessel-like material in the choriocapillary was observed in 3 eyes (9.0%). At month 3 after PDT, the choriocapillary layer of OCTA was shown to return to normal in 32 eyes (97%). Conclusions: We have detected choriocapillary changes in patients diagnosed with CCSC following half-dose PDT by using noninvasive OCTA. These findings provide new evidence in support of the previously proposed hypothesis on the effect of PDT and suggest that OCTA may become a useful tool in the follow-up of CCSC.

Optical coherence tomographic angiography of choroidal neovascularization ill-defined with fluorescein angiography

PurposeTo evaluate the morphological structure of ill-defined choroidal neovascularisation (CNV) with traditional fluorescein angiography (FA) compared with optical coherence tomographic angiography (OCTA).MethodsA retrospective case series study of 11 eyes with...

Microcirculatory Responses to Hyperoxia in Macular and Peripapillary Regions.

To evaluate the hyperoxia response of the retinal vascular system in different parts of the fundus using optical coherence tomography (OCT) angiography. Using an OCT angiography system and a split-spectrum amplitude decorrelation angiography (SSADA) algorithm, perfused vessel density at the macular and peripapillary regions was measured before and after breathing 80% oxygen in 10 healthy Chinese subjects. The repeatability of the hyperoxia response was also tested. Hyperoxia provocation caused a significant decrease in retinal perfused vessel density in both the macular and peripapillary areas. The para- and perifoveal area had a mean reduction of 13.66% and 15.17%, respectively; these reductions were significantly greater than in the peripapillary area (9.52%; parafovea versus peripapillary, P = 0.023; perifovea versus peripapillary, P = 0.006). The coefficients of variation (CV), intraclass correlations (ICC), and Bland-Altman plots suggested strong repeatability of the hyperoxia response. The optical coherence tomography system, in conjunction with the SSADA algorithm, recorded a significant reduction in retinal perfused vessel density after hyperoxia, and the reduction was greater in the macular area than in the peripapillary area.

Compensation for Reflectance Variation in Vessel Density Quantification by Optical Coherence Tomography Angiography.

PurposeTo compensate for reflectance variation when quantifying vessel density by optical coherence tomography angiography (OCTA).MethodsHealthy participants received 6×6-mm macular and 4.5×4.5-mm optic nerve head (ONH) angiography scans on a 70-kHz spectral-domain optical coherence tomography system. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to compute the OCTA signal. Mean reflectance projection and maximum decorrelation projection were used to create en face OCT and OCTA images. Background OCTA noise in static tissue was evaluated in the foveal avascular zone (FAZ). Vessel density was calculated from en face retinal OCTA that was binarized according to a decorrelation threshold.ResultsThe average retinal decorrelation noise in the FAZ was linearly related to the average logarithmic-scale OCT reflectance signal. Based on this relationship, a reflectance-adjusted decorrelation threshold equation was developed to filter out 97.5% of background OCTA noise. A fixed threshold was also used for comparison. The superficial vascular complex vessel density in the macula and ONH were significantly correlated with reflectance signal strength index (SSI) using the fixed threshold. This correlation was removed by using the reflectance-adjusted threshold. Reflectance compensation reduced population variation in 25 healthy eyes from 8.5% to 4.8% (coefficient of variation) in the macula and from 6.7% to 5.4% in the peripapillary region. Within-visit repeatability also improved from 4.4% to 1.8% in the macula and from 3% to 1.7% in the peripapillary region.ConclusionsCompensating for reflectance variation resulted in more reliable vessel density quantification in OCTA.

Macular microvasculature alterations in patients with primary open-angle glaucoma: A cross-sectional study.

To evaluate and compare macular microvasculature changes in eyes with primary open-angle glaucoma (POAG) to normal eyes, and to assess associations among the retinal microvasculature, neural structural damage, and visual field loss.Ninety-nine eyes (68 patients with POAG and 31 normal subjects) were enrolled in this study. Thirty-five eyes with early-stage glaucoma (EG), 33 eyes with advanced-stage glaucoma (AG), and 31 normal eyes were included. An optical coherence tomography system with a split-spectrum amplitude-decorrelation angiography algorithm was used to measure the macular capillary vessel area density and retinal thickness. Visual field testing (30-2 and 10-2 programs) was performed using a Humphrey field analyzer. Correlations between the capillary vessel area density, retinal thickness, and visual field parameters were analyzed.Compared to normal eyes, those with EG and AG had a lower macular capillary vessel area density and lesser retinal thickness (P < 0.001, all). Results of multivariate linear regression analyses showed that each standard deviation (SD) decrease in the vessel area density was associated with a 1.5% and 4.2% thinning of the full retinal thickness and inner retinal layer thickness, respectively. Each SD decrease in the vessel area density was also associated with a 12.9% decrease in the mean sensitivity and a 33.6% increase in the pattern standard deviation (P < 0.001, both). The Pearson partial regression analysis model showed that the vessel area density was most strongly associated with the inner retinal layer thickness and inferior hemimacular thickness. Furthermore, a lower vessel area density was strongly associated with a more severe hemimacular visual field defect and the corresponding hemimacular retinal thickness.The macular capillary vessel area density and retinal thickness were significantly lower in eyes with POAG than in normal eyes. A diminished macular microvasculature network is closely associated with visual field defects, which are dependent on structural damage due to POAG.

Evaluating Polypoidal Choroidal Vasculopathy With Optical Coherence Tomography Angiography.

PurposeWe observed and analyzed the morphologic characteristics of polypoidal lesions and abnormal branching vascular network (BVN) in patients with polypoidal choroidal vasculopathy (PCV) by optical coherence tomography angiography (OCTA).MethodsA retrospective observational case series was done of patients with PCV. All patients were scanned with a 70-kHz spectral-domain OCT system using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm to distinguish blood flow from static tissue. The OCTA images of these patients were compared to those from indocyanine green angiography (ICGA). Semiautomated segmentation was used to further analyze the polypoidal lesion and the BVN.ResultsWe studied 13 eyes of 13 patients 51 to 69 years old. A total of 11 patients were treatment-naive. Two patients had multiple anti-VEGF injections and one underwent photodynamic therapy (PDT). Optical coherence tomography angiography was able to detect the BVN in all cases. Using cross-sectional OCTA, BVN locations were shown to be in the space between the RPE and Bruch's membrane. Using en face OCTA, the BVN vascular pattern could be shown more clearly than by ICGA. Polypoidal lesions showed high flow signals in different patterns in 12 cases in the outer retina slab. Using cross-sectional OCTA, the polyps were shown to be just below the top of the pigment epithelial detachment (PED). In one case, the polypoidal lesion was not detectable at the outer retina slab.ConclusionsOptical coherence tomography angiography is a noninvasive imaging tool for detecting vascular changes in PCV. Branching vascular networks showed more clearly on OCTA than on ICGA. Polypoidal lesions had variable patterns on OCTA and were not always detected. The OCTA patterns of the polypoidal lesions and the BVN are helpful in understanding the pathology of PCV.

The role of optical coherence tomography angiography in fundus vascular abnormalities.

BackgroundTo evaluate the role of optical coherence tomography angiography (OCTA) in observation of fundus vascular abnormalities.MethodsPatients (n = 50, 10 in each group) with fundus disorders including branch retinal vein occlusion (BRVO), non-proliferative diabetic retinopathy (NPDR), proliferative diabetic retinopathy (PDR), exudative age-related macular degeneration (AMD), and polypoidal choroidal vasculopathy (PCV) were examined. They underwent imaging of OCTA and fluorescein angiography/indocyanine green angiography. The split-spectrum amplitude-decorrelation angiography algorithm was employed to obtain angiography within a 6 × 6 mm scanning area at the posterior retina. Segmentation algorithm was used to obtain 2-dimensional images from arbitrary layers. The OCTA features were analyzed and compared with the findings of conventional angiography. The contralateral eyes of the patients with BRVO and the eyes of 20 healthy volunteers served as controls.ResultsOCTA showed precise images of normal and abnormal vasculature in the posterior retina and choroid by the given layers. Vascular abnormalities such as enlarged foveal avascular zone (FAZ), non-perfusion area of retina, microaneurysm, retinal neovascularization, choroidal neovascularization (CNV), branching vascular network and polypoidal lesions in choroid were clearly displayed by OCTA.ConclusionsOCTA provided a better projection of vascular pathologies of the posterior retina and choroid and could determine the precise location of the vascular lesion. The noninvasive OCTA can benefit the diagnosis of vascular abnormalities in the posterior retina and choroid.

Reproducibility of Perfusion Parameters of Optic Disc and Macula in Rhesus Monkeys by Optical Coherence Tomography Angiography.

Background:Optical coherence tomography (OCT) angiography is a novel technique by which we can detect the local perfusion of fundus directly. The aim of this study was to evaluate the reproducibility of optic disc and macular flow perfusion parameters in rhesus monkeys using OCT angiography.Methods:Eighteen healthy monkeys (18 eyes) were subjected to optic disc and macula flow index measurements via a high-speed and high-resolution spectral-domain OCT XR Avanti with a split-spectrum amplitude de-correlation angiography algorithm. Right eye was imaged 3 times during the first examination and once during each of the two following examinations. The intra-visit and inter-visit intraclass correlation coefficients (ICCs) were both determined.Results:The average flow indices of the four optic disc area layers were 0.171 ± 0.009 (optic nerve head), 0.015 ± 0.004 (vitreous), 0.052 ± 0.009 (radial peripapillary capillary), and 0.167 ± 0.011 (choroid). Average flow indices of the four macula area layers were 0.044 ± 0.011 (superficial retina), 0.036 ± 0.011 (deep retina), 0.016 ± 0.009 (outer retina), and 0.155 ± 0.013 (choroid). Intra-visit (ICC value: 0.821–0.954) and inter-visit (ICC value: 0.844–0.899) repeatability were both high.Conclusions:The study is about the reproducibility of optic disc and macular perfusion parameters as measured by OCT angiography in healthy rhesus monkeys. Flow index measurement reproducibility is high for both the optic disc and macula of normal monkey eyes. OCT angiography might be a useful technique to assess changes when examining monkeys with experimental ocular diseases.

OCT angiography in the mouse: A novel evaluation method for vascular pathologies of the mouse retina

PurposeTo investigate the application of optical coherence tomography (OCT) angiography in the retinas of healthy mice and to evaluate choroidal neovascularization (CNV) in a mouse model of laser-induced CNV. MethodsC57BL/6J mice aged 18–25 weeks were examined using the spectral-domain optical coherence tomography device RTVue XR Avanti (Optovue, Inc, Fremont, California, USA). Blood flow in different retinal layers was detected using the split-spectrum amplitude-decorrelation angiography algorithm. Fluorescein angiography (FA) images were obtained using the Heidelberg Spectralis device (Heidelberg, Germany). ResultsUsing the RTVue XR Avanti, we were able to obtain high-quality OCT angiography images of normal vasculature in the superficial, deep capillary and choriocapillary layers in laser-treated mice and untreated controls. Whereas no blood flow was detectable in the outer retina of untreated mice, blood flow and hence neovascular vessels were found in laser-treated mice. ConclusionsOCT angiography can clearly visualize the normal vascular plexus in the different retinal layers in the mouse retina and choroid. With OCT angiography, it is possible to verify the choroidal neovascularization induced by laser treatment. Thus, OCT angiography is a helpful imaging tool for non-invasive, in vivo evaluation of laser-induced CNV in the mouse.

Optical coherence tomography angiography in glaucoma diagnosis

According to literature data, vascular dysfunction may well contribute to the development of glaucomatous optic neuropathy, which makes it reasonable to search for new imaging techniques capable of early diagnosis and monitoring of glaucoma through assessment of retinal, optic nerve head (ONH), and choroidal perfusion. Optical coherence tomography angiography (OCTA), a recently introduced method based on the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm, enables evaluation of both retinal and choroidal blood flow in peripapillary and macular areas. The first studies involving OCTA have revealed a decrease in retinal blood flow in glaucoma. It has also been shown that visual field indices correlate better with the peripapillary flow index than with morphometric parameters of the optic nerve head (ONH) and peripapillary retina. OCT angiography has great potential for ONH blood flow assessment during physiological tests, which is an important step towards understanding pathogenesis of glaucoma.

Optical Coherence Tomography Angiography in Retinal Diseases.

Optical coherence tomography angiography (OCTA) is a new, non-invasive imaging system that generates volumetric data of retinal and choroidal layers. It has the ability to show both structural and blood flow information. Split-spectrum amplitude-decorrelation angiography (SSADA) algorithm (a vital component of OCTA software) helps to decrease the signal to noise ratio of flow detection thus enhancing visualization of retinal vasculature using motion contrast. Published studies describe potential efficacy for OCTA in the evaluation of common ophthalmologic diseases such as diabetic retinopathy, age related macular degeneration (AMD), retinal vascular occlusions and sickle cell disease. OCTA provides a detailed view of the retinal vasculature, which allows accurate delineation of microvascular abnormalities in diabetic eyes and vascular occlusions. It helps quantify vascular compromise depending upon the severity of diabetic retinopathy. OCTA can also elucidate the presence of choroidal neovascularization (CNV) in wet AMD. In this paper, we review the knowledge, available in English language publications regarding OCTA, and compare it with the conventional angiographic standard, fluorescein angiography (FA). Finally, we summarize its potential applications to retinal vascular diseases. Its current limitations include a relatively small field of view, inability to show leakage, and tendency for image artifacts. Further larger studies will define OCTA's utility in clinical settings and establish if the technology may offer a non-invasive option of visualizing the retinal vasculature, enabling us to decrease morbidity through early detection and intervention in retinal diseases.

Optical Coherence Tomography Angiography Using the Optovue Device.

Optovue AngioVue system technology for optical coherence tomography (OCT) angiography is based on the AngioVue Imaging System (Optovue, Inc., Freemont, CA), using split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. This algorithm was developed to minimize scanning time. It detects motion in blood vessel lumen by measuring the variation in reflected OCT signal amplitude between consecutive cross-sectional scans. The novelty of SSADA lies in how the OCT signal is processed to enhance flow detection and reject axial bulk motion noise. Specifically, the algorithm splits the OCT image into different spectral bands, thus increasing the number of usable image frames. Each new frame has a lower axial resolution that is less susceptible to axial eye motion caused by blood pulsation. Optovue AngioVue system technology allows quantitative analysis. It provides numerical data about flow area and non-flow area. It can also generate a flow density map. These metrics may serve as biomarkers in diagnosis and for tracking disease progression or treatment response. Flow area: the software will calculate the drawn area and vessel area in mm(2). It allows for comparison of all measurements for a given participant. Non-flow area: the software shows the non-perfused areas by mouse click selection. Ischemic areas will be shown in yellow. These areas may be saved and matched with others in the study. Flow density tool is able to measure the percentage of vascular areas on en face angiograms. This analysis is based on an ETDRS grid centered on the macula as with the thickness map. This tool works both on inner and outer vascular plexus.

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY FEATURES OF DIABETIC RETINOPATHY.

To describe the optical coherence tomography angiography features of diabetic retinopathy. Using a 70 kHz optical coherence tomography and the split-spectrum amplitude decorrelation angiography algorithm, 6 mm × 6 mm 3-dimensional angiograms of the macula of 4 patients with diabetic retinopathy were obtained and compared with fluorescein angiography for features cataloged by the Early Treatment of Diabetic Retinopathy Study. Optical coherence tomography angiography detected enlargement and distortion of the foveal avascular zone, retinal capillary dropout, and pruning of arteriolar branches. Areas of capillary loss obscured by fluorescein leakage on fluorescein angiography were more clearly defined on optical coherence tomography angiography. Some areas of focal leakage on fluorescein angiography that were thought to be microaneurysms were found to be small tufts of neovascularization that extended above the inner limiting membrane. Optical coherence tomography angiography does not show leakage but can better delineate areas of capillary dropout and detect early retinal neovascularization. This new noninvasive angiography technology may be useful for routine surveillance of proliferative and ischemic changes in diabetic retinopathy.

Reproducibility and repeatability of foveal avascular zone measurements in healthy subjects by optical coherence tomography angiography

Background/aimsTo assess the reproducibility and repeatability of foveal avascular zone (FAZ) area measurements using optical coherence tomography angiography (OCT-A) in healthy subjects.MethodsSixty healthy volunteers (60 eyes) were subjected to FAZ...

Optical Coherence Tomography Angiography of the Peripapillary Retina in Glaucoma.

Vascular factors may have important roles in the pathophysiology of glaucoma. A practical method for the clinical evaluation of ocular perfusion is needed to improve glaucoma management. To detect peripapillary retinal perfusion in glaucomatous eyes compared with normal eyes using optical coherence tomography (OCT) angiography. Prospective observational study performed from July 24, 2013, to April 17, 2014. Participants were recruited and tested at Casey Eye Institute, Oregon Health & Science University. In total, 12 glaucomatous eyes and 12 age-matched normal eyes were analyzed. The optic disc region was imaged twice using a 3 × 3-mm scan by a 70-kHz, 840-nm-wavelength spectral OCT system. The split-spectrum amplitude-decorrelation angiography algorithm was used. Peripapillary flow index was calculated as the mean decorrelation value in the peripapillary region, defined as a 700-µm-wide elliptical annulus around the disc. Peripapillary vessel density was the percentage area occupied by vessels. The data statistical analysis was performed from October 30, 2013, to May 30, 2014. Variability was assessed by the coefficient of variation. The Mann-Whitney test was used to compare the 2 groups of eyes. Correlations between vascular and visual field variables were assessed by linear regression analysis. In 12 normal eyes, a dense microvascular network around the disc was visible on OCT angiography. In 12 glaucomatous eyes, this network was visibly attenuated globally and focally. In normal eyes, between-visit reproducibilities of peripapillary flow index and peripapillary vessel density were 4.3% and 2.7% of the coefficient of variation, respectively, while the population variabilities of peripapillary flow index and peripapillary vessel density were 8.2% and 3.0% of the coefficient of variation, respectively. Peripapillary flow index and peripapillary vessel density in glaucomatous eyes were lower than those in normal eyes (P < .001 for both). Peripapillary flow index (Pearson r = -0.808) and peripapillary vessel density (Pearson r = -0.835) were highly correlated with visual field pattern standard deviation in glaucomatous eyes (P = .001 for both). The areas under the receiver operating characteristic curve for normal vs glaucomatous eyes were 0.892 for peripapillary flow index and 0.938 for peripapillary vessel density. Using OCT angiography, reduced peripapillary retinal perfusion in glaucomatous eyes can be visualized as focal defects and quantified as peripapillary flow index and peripapillary vessel density, with high repeatability and reproducibility. Quantitative OCT angiography may have value in future studies to determine its potential usefulness in glaucoma evaluation.

En face optical coherence tomography angiography for corneal neovascularisation

Background/aimRecently, there has been an increasing clinical need for objective evaluation of corneal neovascularisation, a condition which cause significant ocular morbidity. We describe the use of a rapid, non-invasive ‘en...

Chronic Central Serous Chorioretinopathy Imaged by Optical Coherence Tomographic Angiography

To describe optical coherence tomographic (OCT) angiography findings in chronic central serous chorioretinopathy (CSC), and to characterize their OCT B-scans by means of the split-spectrum amplitude-decorrelation angiography algorithm. Evaluation of an imaging technique in a cohort of patients. Fluorescein (FA) and indocyanine green (ICGA) angiography (Heidelberg Spectralis, Heidelberg, Germany), OCT angiography, and OCT angiography with the split-spectrum amplitude-decorrelation angiography algorithm (XR Optovue, Fremont, California, USA) were performed. A qualitative analysis of the entire imaging data was done. Twelve eyes of 10 patients were included. Mean visual acuity was 20/30. All eyes presented findings consistent with chronic CSC (lasting more than 6months) on biomicroscopic examination, autofluorescence, FA, ICGA, and OCT. ICGA showed the characteristic choroidal hyperpermeability, while there was no evidence of choroidal neovascularization (CNV). OCT B-scans showed 2 distinct profiles of the retinal pigment epithelium (RPE): a slight RPE detachment with small undulations was evident in 7 of 12 eyes, while 5 eyes presented a flat RPE profile. OCT angiography in 7 eyes (58%) revealed the presence of a distinct CNV corresponding to the ICGA hyperpermeability. The qualitative analysis of the OCT B-scans compared to the OCT angiographic images demonstrated that the CNV corresponded to the small undulationswithin the slight RPE detachment, confirming its vascularized nature. On the contrary, OCT angiography showed a normal choroidal circulation in the remaining 5 eyes (42%) with a flat RPE profile. OCT angiography allows detection ofCNV in chronic CSC not visible with other imaging techniques. CNV corresponds to the small undulating RPE detachment on B-scan. This might allow an appropriatetreatment resulting in a better visual outcome.

Optical Coherence Tomography Angiography for Anterior Segment Vasculature Imaging

To evaluate the application of an optical coherence tomography angiography (OCTA) system adapted for the assessment of anterior segment vasculature. Cross-sectional, observational study. Consecutive subjects with normal eyes on slit-lamp clinical examination and patients with abnormal corneal neovascularization. All scans were performed using a commercially available AngioVue OCTA system (Optovue, Inc., Fremont, CA) using an anterior segment lens adapter and the split-spectrum amplitude decorrelation angiography algorithm. Each subject underwent scans from 4 quadrants (superior, inferior, nasal, and temporal) in each eye by 2 trained, independent operators. Analysis of signal strength, image quality, and reproducibility of corneal vascular measurements was performed. In our study of 20 normal subjects (10 men, 10 women; mean age, 25.3±7.8 years), we found good repeatability (κ coefficient, 0.76) for image quality score and good interobserver agreement for vasculature measurements (intraclass coefficient, 0.94). After optimization of the angiography scan protocol, vascular measurements within the regions of interest were compared in the superior versus inferior quadrants (mean vascular loops, 3.34±1.16 vs. 3.12 ± 0.90 [P = 0.768]; segment-to-loop ratio, 4.18±0.71 vs. 4.32±0.87 [P = 0.129]; fractal dimension [Df] value, 1.78±0.06 vs. 1.78±0.06 [P = 0.94]; vascular loop area, 25.9±14.5 vs. 25.9±10.7 × 10(-3) mm(2) [P = 0.21]) and nasal versus temporal quadrant (mean vascular loops, 2.89±0.98 vs. 3.57±0.99 [P < 0.001]; segment-to-loop ratio, 3.94±0.69 vs. 4.55±0.78 [P = 0.897]; Df value, 1.78±0.06 vs. 1.77±0.06 [P = 0.14]; vascular loop area, 29.7±15.7 vs. 22.1±7.1 × 10(-3) mm(2) [P = 0.38]. We then used the established OCTA scanning protocol to visualize abnormal vasculature successfully in 5 patients with various corneal pathologic features, including graft-associated neovascularization, postherpetic keratitis scarring, lipid keratopathy, and limbal stem cell deficiency. This preliminary study describes a method for acquiring OCTA images of the cornea and limbal vasculature with substantial consistency. This technique may be useful for the objective evaluation of corneal neovascularization in the future.

Optical Coherence Tomography Angiography of Peripapillary Retinal Blood Flow Response to Hyperoxia.

To measure the change in peripapillary retinal blood flow in response to hyperoxia by using optical coherence tomography (OCT) angiography. One eye of each healthy human participants (six) was scanned with a commercial high-speed (70 kHz) spectral OCT. Scans were captured twice after 10-minute exposures to normal breathing (baseline) and hyperoxia. Blood flow was detected by the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Peripapillary retinal blood flow index and vessel density were calculated from en face maximum projections of the retinal layers. The experiment was performed on 2 separate days for each participant. Coefficient of variation (CV) was used to measure within-day repeatability and between-day reproducibility. Paired t-tests were used to compare means of baseline and hyperoxic peripapillary retinal blood flow. A decrease of 8.87% ± 3.09% (mean ± standard deviation) in flow index and 2.61% ± 1.50% in vessel density was observed under hyperoxia. The within-day repeatability CV of baseline measurements was 5.75% for flow index and 1.67% for vessel density. The between-day reproducibility CV for baseline flow index and vessel density was 11.1% and 1.14%, respectively. The between-day reproducibility of the hyperoxic response was 3.71% and 1.67% for flow index and vessel density, respectively. Optical coherence tomography angiography with SSADA was able to detect a decrease in peripapillary retinal blood flow in response to hyperoxia. The response was larger than the variability of baseline measurements. The magnitude of an individual's hyperoxic response was highly variable between days. Thus, reliable assessment may require averaging multiple measurements.

Macular Perfusion in Healthy Chinese: An Optical Coherence Tomography Angiogram Study

To investigate macular perfusion in healthy Chinese individuals and examine its dependence on age and sex. Healthy adult Chinese individuals were recruited. Macular perfusion was measured by spectral-domain optical coherence tomography (OCT) using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. The parafoveal flow index and vessel area density as well as the area of the foveal capillary-free zone (CFZ) were quantified. A total of 76 eyes in 45 subjects were included (20 males and 25 females, mean age 36 ± 11 years). The mean parafoveal flow index was 0.099 ± 0.013; the mean vessel area density was 0.891 ± 0.073; and the mean CFZ area was 0.474 ± 0.172 mm2. All three parameters were significantly correlated with age (flow index: P = 0.00; vessel area density: P = 0.00; CFZ area: P = 0.02). The flow index and vessel area density decreased annually by 0.6% and 0.4%, respectively, and CFZ area increased by 1.48% annually. The CFZ area was larger in females than in males, while all three parameters seemed to change more rapidly with age in males than in females. In healthy Chinese eyes, macular perfusion decreased with increasing age, and decreased more rapidly in males than in females. The application of OCT angiograms may provide a useful approach for monitoring macular perfusion, although caution must be exercised with regard to age- and sex-related variations.