Real-Time Automatic Segmentation of Optical Coherence Tomography Volume Data of the Macular Region.

Optical coherence tomography (OCT) is a high speed, high resolution and non-invasive imaging modality that enables the capturing of the 3D structure of the retina. The fast and automatic analysis of 3D volume OCT data is crucial taking into account the increased amount of patient-specific 3D imaging data. In this work, we have developed an automatic algorithm, OCTRIMA 3D (OCT Retinal IMage Analysis 3D), that could segment OCT volume data in the macular region fast and accurately. The proposed method is implemented using the shortest-path based graph search, which detects the retinal boundaries by searching the shortest-path between two end nodes using Dijkstra's algorithm. Additional techniques, such as inter-frame flattening, inter-frame search region refinement, masking and biasing were introduced to exploit the spatial dependency between adjacent frames for the reduction of the processing time. Our segmentation algorithm was evaluated by comparing with the manual labelings and three state of the art graph-based segmentation methods. The processing time for the whole OCT volume of 496x644x51 voxels (captured by Spectralis SD-OCT) was 26.15 seconds which is at least a 2-8-fold increase in speed compared to other, similar reference algorithms used in the comparisons. The average unsigned error was about 1 pixel ( approximately 4 microns), which was also lower compared to the reference algorithms. We believe that OCTRIMA 3D is a leap forward towards achieving reliable, real-time analysis of 3D OCT retinal data

In Vivo Evaluation of Retinal Neurodegeneration in Patients with Multiple Sclerosis

To evaluate macular morphology in the eyes of patients with multiple sclerosis (MS) with or without optic neuritis (ON) in previous history.Optical coherence tomography (OCT) examination was performed in thirty-nine patients with MS and in thirty-three healthy subjects. The raw macular OCT data were processed using OCTRIMA software. The circumpapillary retinal nerve fiber layer (RNFL) thickness and the weighted mean thickness of the total retina and 6 intraretinal layers were obtained for each eye. The eyes of MS patients were divided into a group of 39 ON-affected eyes, and into a group of 34 eyes with no history of ON for the statistical analyses. Receiver operating characteristic (ROC) curves were constructed to determine which parameter can discriminate best between the non-affected group and controls.The circumpapillary RNFL thickness was significantly decreased in the non-affected eyes compared to controls group only in the temporal quadrant (p = 0.001) while it was decreased in the affected eyes of the MS patients in all quadrants compared to the non-affected eyes (p<0.05 in each comparison). The thickness of the total retina, RNFL, ganglion cell layer and inner plexiform layer complex (GCL+IPL) and ganglion cell complex (GCC, comprising the RNFL and GCL+IPL) in the macula was significantly decreased in the non-affected eyes compared to controls (p<0.05 for each comparison) and in the ON-affected eyes compared to the non-affected eyes (p<0.001 for each comparison). The largest area under the ROC curve (0.892) was obtained for the weighted mean thickness of the GCC. The EDSS score showed the strongest correlation with the GCL+IPL and GCC thickness (p = 0.007, r = 0.43 for both variables).Thinning of the inner retinal layers is present in eyes of MS patients regardless of previous ON. Macular OCT image segmentation might provide a better insight into the pathology of neuronal loss and could therefore play an important role in the diagnosis and follow-up of patients with MS

Investigating Tissue Optical Properties and Texture Descriptors of the Retina in Patients with Multiple Sclerosis

PURPOSE: To assess the differences in texture descriptors and optical properties of retinal tissue layers in patients with multiple sclerosis (MS) and to evaluate their usefulness in the detection of neurodegenerative changes using optical coherence tomography (OCT) image segmentation. PATIENTS AND METHODS: 38 patients with MS were examined using Stratus OCT. The raw macular OCT data were exported and processed using OCTRIMA software. The enrolled eyes were divided into two groups, based on the presence of optic neuritis (ON) in the history (MSON+ group, n = 36 and MSON- group, n = 31). Data of 29 eyes of 24 healthy subjects (H) were used as controls. A total of seven intraretinal layers were segmented and thickness as well as optical parameters such as contrast, fractal dimension, layer index and total reflectance were measured. Mixed-model ANOVA analysis was used for statistical comparisons. RESULTS: Significant thinning of the retinal nerve fiber layer (RNFL), ganglion cell/inner plexiform layer complex (GCL+IPL) and ganglion cell complex (GCC, RNFL+GCL+IPL) was observed between study groups in all comparisons. Significant difference was found in contrast in the RNFL, GCL+IPL, GCC, inner nuclear layer (INL) and outer plexiform layer when comparing MSON+ to the other groups. Higher fractal dimension values were observed in GCL+IPL and INL layers when comparing H vs. MSON+ groups. A significant difference was found in layer index in the RNFL, GCL+IPL and GCC layers in all comparisons. A significant difference was observed in total reflectance in the RNFL, GCL+IPL and GCC layers between the three examination groups. CONCLUSION: Texture and optical properties of the retinal tissue undergo pronounced changes in MS even without optic neuritis. Our results may help to further improve the diagnostic efficacy of OCT in MS and neurodegeneration

The Effect of Axial Length on the Thickness of Intraretinal Layers of the Macula.

PURPOSE: The aim of this study was to evaluate the effect of axial length (AL) on the thickness of intraretinal layers in the macula using optical coherence tomography (OCT) image analysis. METHODS: Fifty three randomly selected eyes of 53 healthy subjects were recruited for this study. The median age of the participants was 29 years (range: 6 to 67 years). AL was measured for each eye using a Lenstar LS 900 device. OCT imaging of the macula was also performed by Stratus OCT. OCTRIMA software was used to process the raw OCT scans and to determine the weighted mean thickness of 6 intraretinal layers and the total retina. Partial correlation test was performed to assess the correlation between the AL and the thickness values. RESULTS: Total retinal thickness showed moderate negative correlation with AL (r = -0.378, p = 0.0007), while no correlation was observed between the thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer (GCC), retinal pigment epithelium (RPE) and AL. Moderate negative correlation was observed also between the thickness of the ganglion cell layer and inner plexiform layer complex (GCL+IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL) and AL which were more pronounced in the peripheral ring (r = -0.402, p = 0.004; r = -0.429, p = 0.002; r = -0.360, p = 0.01; r = -0.448, p = 0.001). CONCLUSIONS: Our results have shown that the thickness of the nuclear layers and the total retina is correlated with AL. The reason underlying this could be the lateral stretching capability of these layers; however, further research is warranted to prove this theory. Our results suggest that the effect of AL on retinal layers should be taken into account in future studies

A morphological study of retinal changes in unilateral amblyopia using optical coherence tomography image segmentation.

OBJECTIVE: The purpose of this study was to evaluate the possible structural changes of the macula in patients with unilateral amblyopia using optical coherence tomography (OCT) image segmentation. PATIENTS AND METHODS: 38 consecutive patients (16 male; mean age 32.4+/-17.6 years; range 6-67 years) with unilateral amblyopia were involved in this study. OCT examinations were performed with a time-domain OCT device, and a custom-built OCT image analysis software (OCTRIMA) was used for OCT image segmentation. The axial length (AL) was measured by a LenStar LS 900 device. Macular layer thickness, AL and manifest spherical equivalent refraction (MRSE) of the amblyopic eye were compared to that of the fellow eye. We studied if the type of amblyopia (strabismus without anisometropia, anisometropia without strabismus, strabismus with anisometropia) had any influence on macular layer thickness values. RESULTS: There was significant difference between the amblyopic and fellow eyes in MRSE and AL in all subgroups. Comparing the amblyopic and fellow eyes, we found a statistically significant difference only in the thickness of the outer nuclear layer in the central region using linear mixed model analysis keeping AL and age under control (p = 0.032). There was no significant difference in interocular difference in the thickness of any macular layers between the subgroups with one-way between-groups ANCOVA while statistically controlling for interocular difference in AL and age. CONCLUSIONS: According to our results there are subtle changes in amblyopic eyes affecting the outer nuclear layer of the fovea suggesting the possible involvement of the photoreceptors. However, further studies are warranted to support this hypothesis

Retinal Microvascular Network Alterations: Potential Biomarkers of Cerebrovascular and Neural Diseases

Increasing evidence suggests that the conditions of retinal microvessels are indicators to a variety of cerebrovascular, neurodegenerative, psychiatric, and developmental diseases. Thus noninvasive visualization of the human retinal microcirculation offers an exceptional opportunity for the investigation of not only the retinal but also cerebral microvasculature. In this review, we show how the conditions of the retinal microvessels could be used to assess the conditions of brain microvessels because the microvascular network of the retina and brain share, in many aspects, standard features in development, morphology, function, and pathophysiology. Recent techniques and imaging modalities, such as optical coherence tomography (OCT), allow more precise visualization of various layers of the retina and its microcirculation, providing a microscope to brain microvessels. We also review the potential role of retinal microvessels in the risk identification of cerebrovascular and neurodegenerative diseases. The association between vision problems and cerebrovascular and neurodegenerative diseases, as well as the possible role of retinal microvascular imaging biomarkers in cerebrovascular and neurodegenerative screening, their potentials, and limitations, are also discussed

Messung der retinalen Blutflussgeschwindigkeit bei Patienten mit retinaler Vaskulitis

Hintergrund: Beim Retinal Function Imager (RFI) (Optical Imaging Ltd., Israel) handelt es sich um ein bildgebendes Gerät, welches mit einer „high resolution“ Technik ausgestattet ist und zur Messung der Blutflussgeschwindigkeit in den sekundären und tertiären retinalen Arterien und Venen genutzt wird. Dies geschieht unter der Verwendung von stroboskopischem Licht, welches die Autofluoreszenz der Erythrozyten anregt, sodass die Gabe eines intravenösen Kontrastmittels überflüssig wird. Wir haben die Funktion dieses Gerätes, welches vorwiegend bei Patienten mit Diabetes mellitus zum Ausschluss einer Präretinopathie eingesetzt wird, erstmals dazu genutzt, um die retinale Durchblutungssituation bei Patienten mit einer retinalen Vaskulitis darzustellen. Methoden: Untersucht wurden in einer Pilotstudie 9 Patienten (m:w = 2:7) mit einem mittleren Alter von 51 ± 11 Jahren. Sieben dieser Patienten litten unter einer Birdshot Chorioretinopathie, 2 Patienten wiesen eine retinale Vaskulitis unklarer Genese auf. Verglichen wurden diese Patienten mit einer augengesunden Kontrollgruppe. Ergebnisse: Währenddessen die Kontrollgruppe eine arterielle Blutflussgeschwindigkeit von 4,1 ± 0,9 mm/s und eine venöse Fließgeschwindigkeit von 2,9 ± 1,0 mm/s aufwies, zeigten sich in der Gruppe der Patienten mit retinaler Vaskulitis signifikante Unterschiede. Die arterielle wie auch die venöse Blutflussgeschwindigkeit der Patienten waren mit 2,5 ± 1,6 mm/s (p < 0,00001) bzw. mit 1,8 ± 1,0 mm/s (p = 0,00001) signifikant reduziert. Schlussfolgerungen: Mit dem Retinal Function Imager konnte erstmals gezeigt werden, dass eine retinale Vaskulitis eine signifikante Reduktion sowohl des arteriellen als auch des venösen retinalen Blutflusses zur Folge ab. Daher scheint der RFI nicht nur zur Diagnose sondern möglicherweise auch zur Verlaufskontrolle und zur Berurteilung der Effektivität der Therapie eingesetzt werden zu können

Inter-session repeatability of retinal layer thickness in optical coherence tomography

Reliable retinal layer thickness measurements using optical coherence tomography (OCT) are important to track the subtle retinal changes in longitudinal studies. A total of 10 eyes (5 healthy subjects, 40±13 years old) were enrolled to study the inter-session repeatability and identify the pitfalls affecting the reliabilities. Each eye was scanned using spectral domain OCT (Spectralis SDOCT, Heidelberg Engineering) for 3 sessions with 30 seconds rest in between. The first and second sessions were scanned independently and the third one was scanned with the first one as the baseline visit. Each session consisted of a confocal scanning laser ophthalmoscopy (cSLO) image and 61 B-scans of 496×768 pixels. The first, second and third sessions were named as baseline, unregistered and registered sessions; respectively. Seven retinal layers labeled as RNFL, GCL+IPL, INL, OPL, ONL, IS and OS were segmented using a custom software (OCTRIMA3D) and measured in the ETDRS grid. Inter-session standard deviation (σ), coefficient of repeatability (CR) and coefficient of variations (COV) were calculated to quantify the repeatability. Paired t-test of COVs was used to compare the repeatability and the level of significance was set at 5%. We obtained that values of the CR <5 μm and COV of 5%, were revealed only in the outer layers. The values of COV were not significantly different (p<0.05) in the unregistered scanning session. Our results show that the rotations in the unregistered scanning sessions do not cause significant change in repeatability

Evaluation of macular morphology in patients with multiple sclerosis

Purpose To assess macular morphology in patients with multiple sclerosis (MS) with and without history of optic neuritis (ON). Methods Twenty‐six MS patients were recruited in this study, and 26 randomly eyes were selected from 26 age‐matched healthy subjects as controls. Optical coherence tomography (OCT) examination was performed on each eye using a Stratus OCT device. The raw OCT data were exported from the device and further processed using a custom‐built algorithm (OCTRIMA). Thickness measurements of 7 intraretinal layers and the total retina were obtained. Eyes from MS patients were divided into 2 groups for statistical analyses. The ON+ group contained 26 eyes which had ON at least 6 months prior to enrollment. Twenty‐three eyes had no history of ON (ON‐ group). All thickness measurements were compared among the 3 groups using ANOVA with Newman‐Keuls post‐hoc analysis. Results Significant decrease in thickness was observed in ON+ and ON‐ eyes compared to controls for the macula (290±6µm, 283±12µm and 267±12µm in the control, ON‐ and ON+ group, respectively), retinal nerve fiber layer (38±2µm, 35±2µm and 31±4µm, respectively) and ganglion cell layer and inner plexiform layer complex (71±4µm, 64±7µm and 53±7µm, respectively). No statistically significant difference in thickness was found for the remaining intraretinal layers between the 3 groups analyzed. Conclusion Atrophy of the ganglion cells and nerve fibers in the macula of MS patients was observed even without previous history of ON. Therefore, thickness measurements of ganglion cells might be useful in the diagnosis and follow‐up of MS patients

Atrophy of retinal vessels in neovascular age-related macular degeneration following long-term treatment with 20 intravitreal anti-VEGF injections

The study aimed to evaluate the changes in retinal vascular density in exudative age-related macular degeneration (AMD) after long-term anti-VEGF treatment using optical coherence tomography angiography (OCT-A), and to compare these changes with the vascular density in AMD treated for one year and healthy eyes. In our cross-sectional study OCT-A was performed on 60 eyes of 60 patients. Group AMD 20 × consisted of patients receiving long-term (minimum 20 injections) aflibercept therapy (n = 17), and Group AMD one year consisted of patients treated for one year with a treat & extend protocol (n = 25). The vascular density values obtained with OCT-A were compared with an age-matched control group of 18 healthy eyes. We examined the central retinal thickness (CRT), the vascular density of the fovea and parafovea in the superficial and deep retinal plexus, and evaluated the extent of the non-flow area and the foveal avascular zone (FAZ) on a 3 × 3 mm macular region. Kruskal-Wallis test was performed for statistical analysis. In Group AMD 20x, the vascular density of superficial retinal plexus in the fovea (p = 0.0022) and parafovea (p < 0.0001) was significantly lower compared to Group one year and control group. In the deep retinal plexus, vascular density in the fovea (p = 0.0033) was significantly lower in both AMD groups compared to the control group, with no difference in the parafoveal region (p = 0.0774). The extent of non-flow area (p = 0.0003) and FAZ (p = 0.0008) were significantly larger in both AMD groups compared to the control group. There was a significant difference in CRT between those treated for one year and control eyes (p = 0.0036). In our study, we demonstrated that macular vessel density was lower in the foveal area in the superficial retinal plexus in AMD patients after one year and long-term anti-VEGF treatment. These vascular density changes were absent in the parafoveal and whole areas of the deep retinal plexus. Our results indicate that long-term anti-VEGF treatment reduces the vascular density of the superficial retinal plexus to a greater extent compared to the deep retinal plexus