Deformable registration of multimodal retinal images using a weakly supervised deep learning approach

There are different retinal vascular imaging modalities widely used in clinical practice to diagnose different retinal pathologies. The joint analysis of these multimodal images is of increasing interest since each of them provides common and complementary visual information. However, if we want to facilitate the comparison of two images, obtained with different techniques and containing the same retinal region of interest, it will be necessary to make a previous registration of both images. Here, we present a weakly supervised deep learning methodology for robust deformable registration of multimodal retinal images, which is applied to implement a method for the registration of fluorescein angiography (FA) and optical coherence tomography angiography (OCTA) images. This methodology is strongly inspired by VoxelMorph, a general unsupervised deep learning framework of the state of the art for deformable registration of unimodal medical images. The method was evaluated in a public dataset with 172 pairs of FA and superficial plexus OCTA images. The degree of alignment of the common information (blood vessels) and preservation of the non-common information (image background) in the transformed image were measured using the Dice coefficient (DC) and zero-normalized cross-correlation (ZNCC), respectively. The average values of the mentioned metrics, including the standard deviations, were DC = 0.72  ±  0.10 and ZNCC = 0.82  ±  0.04. The time required to obtain each pair of registered images was 0.12 s. These results outperform rigid and deformable registration methods with which our method was compared.

Diabetic Macular Oedema Guidelines: An Australian Perspective

The number of people living with diabetes is expected to rise to 578 million by 2030 and to 700 million by 2045, exacting a severe socioeconomic burden on healthcare systems around the globe. This is also reflected in the increasing numbers of people with ocular complications of diabetes (namely, diabetic macular oedema (DMO) and diabetic retinopathy (DR)). In one study examining the global prevalence of DR, 35% of people with diabetes had some form of DR, 7% had PDR, 7% had DMO, and 10% were affected by these vision-threatening stages. In many regions of the world (Australia included), DR is one of the top three leading causes of vision loss amongst working age adults (20-74 years). In the management of DMO, the landmark ETDRS study demonstrated that moderate visual loss, defined as doubling of the visual angle, can be reduced by 50% or more by focal/grid laser photocoagulation. However, over the last 20 years, antivascular endothelial growth factor (VEGF) and corticosteroid therapies have emerged as alternative options for the management of DMO and provided patients with choices that have higher chances of improving vision than laser alone. In Australia, since the 2008 NHMRC guidelines, there have been significant developments in both the treatment options and treatment schedules for DMO. This working group was therefore assembled to review and address the current management options available in Australia.

Advances in application of swept-source optical coherence tomography angiography in diagnosis and treatment of diabetic retinopathy

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the leading causes of global blinding. More attention should be paid to the diagnosis, treatment and prognosis of DR. Swept-source optical coherence tomography angiography (SS-OCTA) is a novel imaging technique presented in recent years. It can accurately present the various levels of the retina, choriocapillaris, macula, and the optic papillary microcirculation, which is new to the diagnosis and prognosis of DR. However, SS-OCTA is limited by poor fixation or severe media clouding and is susceptible to motion artefacts and segmentation errors. Future limitations need to be addressed and large prospective trials conducted to refine the relevance of SS-OCTA to DR. The present study reviews the advances in clinical application of SS-OCTA in diagnosis, treatment and prognosis of DR.

Aqueous Level of ANGPTL4 Correlates with the OCTA Metrics of Diabetic Macular Edema in NPDR

PURPOSE

To investigate the aqueous levels of angiogenic factors in nonproliferative diabetic retinopathy (NPDR) patients with diabetic macular edema (DME) and to ascertain their association with optical coherence tomography angiography (OCTA) metrics.

METHODS

This study enrolled 21 NPDR eyes with DME (NPDR/DME+), 17 NPDR eyes without DME (NPDR/DME-), and 16 diabetic eyes without retinopathy (DWR). Luminex bead-based multiplex array was used to measure the levels of 25 cytokines. OCTA system with a scan area of 3 × 3 mm was used to measure retinal thickness (RT), retinal volume (RV), superficial vessel density (SVD), deep vessel density (DVD), foveal avascular zone (FAZ) area, perimeter and acircularity index.

RESULTS

The levels of ANGPTL4 were significantly different among the three groups (P < 0.05), in which NPDR/DME+ group had the highest level and NPDR/DME- group had a higher level than the DWR group (all, P < 0.0167). OCTA examination showed that, compared with DWR and NPDR/DME- group, RT and RV increased and the whole/parafoveal DVD decreased in NPDR/DME+ group (all, P < 0.05). Meanwhile, NPDR/DME- group had lower parafoveal DVD than the DWR group (P < 0.05). Correlation analysis showed that the levels of ANGPTL4 were positively correlated with foveal/parafoveal RT and RV and negatively correlated with whole/parafoveal DVD in NPDR patients (all, P < 0.05). As the influencing factor of RT, RV, and DVD, every additional 10³ pg/ml of ANGPTL4 was associated with an increase in foveal and parafoveal RT of 4.299 μm and 3.598 μm, respectively. Every additional 10⁶ pg/ml of ANGPTL4 was associated with an increase in foveal and parafoveal RV of 3.371 mm³ and 17.705 mm³, respectively. Every additional 10⁴ pg/ml of ANGPTL4 was associated with a decrease in whole and parafoveal DVD of 1.705% and 1.799%, respectively.

CONCLUSIONS

The level of ANGPTL4 in aqueous humor of NPDR patients with DME was significantly increased and ANGPTL4 might predict RT, RV, and parafoveal DVD of DME in NPDR patients.

Contribution of optical coherence tomography angiography OCT-A in diabetic maculopathy

Introduction

Diabetic retinopathy (DR) increases the risk of blindness by 25 times. Advanced researchs are justified for better management, leading to the role of Optical Coherence Tomography-Angiography (OCT-A), a new non-invasive imaging technique exploring retinal vascularization.

Our purpose is to identify microvascular macular anomalies of DR on OCT-A with qualitative and quantitative evaluation of their impact on retinal vascularization.

Patients and methods

This is a descriptive cross-sectional study where 120 eyes of 66 diabetic patients were enrolled. All patients were diabetic and went through OCT-A imaging.

Results

Microanevrysms were identified in both superficial capillary plexus (SCP) and deep capillary plexus (DCP) where they were more frequently visualized. Macular edema was present in 16,7% of cases in the SCP, and in 30% in DCP. Edema spaces were more frequently present in DCP (p < 0,05). Capillary nonperfusion areas were identified in 82,5% of cases in SCP and in 60% of cases in DCP. The main peri-foveal vascular density was 18,95 ± 5,37%. The main surface of foveal avascular zone (FAZ) in the SCP was 462,52 μm² and was 555,04 ± 329,11 μm² in the DCP where it was larger.

Conclusion

OCT-A is a modern imaging tool that could be used for the diagnosis and monitoring of DR as well as the understanding of its pathophysiology.

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Retinal microvascular abnormalities on OCT-A are observed in diabetic retinopathy and are proportional to its severity.

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Deep capillary plexus was more severely affected than superficial capillary plexus.

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The assessment of macular ischemia could be based on the identification of areas of vascular rarefaction.

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Quantitative assessment of vascular density and the study of the foveal avascular zone can assess the macular ischemia

Role of Optical Coherence Tomography Angiography Imaging in Patients with Diabetes

PURPOSE OF REVIEW

Ocular manifestations in patients with diabetes mellitus (DM) can present as microvascular changes. These microvascular changes can be challenging to identify on exams, and imaging technologies have commonly aided in the diagnosis and management of patients with DM. Optical coherence tomography angiography (OCTA) provides noninvasive image segmentation of various layers of the retina and choroid. Also, post-processing of images and associated quantitative measurements offer potential clinical enhancements. Our aim is to review the current evidence on the utility of OCTA for patients with DM.

RECENT FINDINGS

Research suggests OCTA to potentially provide potential clinical enhancements and alternative methods in detecting subclinical manifestation of diabetic retinopathy, staging diabetic retinopathy, management of diabetic macular edema, and monitoring of systemic markers in patients with diabetes mellitus. OCTA is a promising but relatively new modality, and differences in terminology, research designs, and image processing techniques provide a difficult landscape to navigate. Standardization within further validation is needed to determine the extent of OCTA's clinical utility, but the current literature suggests the potential for earlier detection of ocular manifestations in patients with DM, additional objective measurements for grading and management, and opportunity for additional biomarkers for treatment outcomes.

Robust multimodal registration of fluorescein angiography and optical coherence tomography angiography images using evolutionary algorithms

Optical coherence tomography angiography (OCTA) and fluorescein angiography (FA) are two different vascular imaging modalities widely used in clinical practice to diagnose and grade different relevant retinal pathologies. Although each of them has its advantages and disadvantages, the joint analysis of the images produced by both techniques to analyze a specific area of the retina is of increasing interest, given that they provide common and complementary visual information. However, in order to facilitate this analysis task, a previous registration of the pair of FA and OCTA images is desirable in order to superimpose their common areas and focus the gaze on the regions of interest. Normally, this task is manually carried out by the expert clinician, but it turns out to be tedious and time-consuming. Here, we present a three-stage methodology for robust multimodal registration of FA and superficial plexus OCTA images. The first one is a preprocessing stage devoted to reducing the noise and segmenting the main vessels in both types of images. The second stage uses the vessel information to do an approximate registration based on template matching. Lastly, the third stage uses an evolutionary algorithm based on differential evolution to refine the previous registration and obtain the optimal registration. The method was evaluated in a dataset with 172 pairs of FA and OCTA images, obtaining a success rate of 98.8%. The best mean execution time of the method was less than 5 s per image.

Indicators of Visual Prognosis in Diabetic Macular Oedema

Diabetic macular oedema (DMO) is an important cause of moderate vision loss in people with diabetes. Advances in imaging technology have shown that a significant proportion of patients with DMO respond sub-optimally to existing treatment options. Identifying associations and predictors of response before treatment is initiated may help in explaining visual prognosis to patients and aid the development of personalized treatment strategies. Imaging features, such as central subfoveal thickness, photoreceptor integrity, disorganization of retinal inner layers, choroidal changes, and macular perfusion, have been reported to be prognostic factors of visual acuity (VA) in DMO. In this review we evaluated each risk factor to understand their relative importance in visual prognostication of DMO eyes post-treatment. Although individually, some of these factors may not be significant predictors, in combination they may form phenotypes that can inform visual prognosis. Stratification based on these phenotypes needs to be developed to progress to personalized medicine for DMO.

Automated Image Alignment for Comparing Microvascular Changes Detected by Fluorescein Angiography and Optical Coherence Tomography Angiography in Diabetic Retinopathy

PURPOSE

To quantitatively compare microvascular features in the macula of patients with diabetic retinopathy (DR) using fluorescein angiography (FA) and optical coherence tomography angiography (OCTA).

METHODS

Patients with DR were recruited from the Cairo University Hospital. FA was performed using a Topcon TRC-50DX or Heidelberg Spectralis HRA+OCT. OCTA was performed using an Optovue RTVue-XR Avanti. FA images were cropped and aligned to the corresponding OCTA images using i2k Align Retina software. The foveal avascular zone (FAZ), area of ischemia, and microaneurysms (MAs) were manually quantified using ImageJ. The fractal dimension (FD) was calculated from each skeletonized image using the FracLac plugin of ImageJ after retinal vascular segmentation.

RESULTS

Twenty-four eyes of 17 patients were evaluated, but only 18 eyes were successfully aligned. There was no difference in FAZ area measured for FA and OCTA images. Compared with OCTA images, FD was significantly less for FA images (1.66 ± 0.048 versus 1.72 ± 0.023, p < .001). Significantly more MAs were identified on FA images (102 ± 27.5) compared with OCTA (47.5 ± 11.7, p < .0001). The number of MAs on FA correlated with decreasing best corrected visual acuity (r² = 0.315, p = .015) and increasing central macular thickness (r² = 0.492, p = .001). No such associations were found with MAs detected on OCTA. Nevertheless, the area of ischemia in the FA images (8.5 ± 4.1%) was significantly smaller compared with the area measured in both the superficial (30.7 ± 9.5%) and deep capillary plexus (21.6 ± 10.9%) of the OCTA (p < .001). Interestingly, number of MAs in the FA images correlated with increasing area of ischemia in the FA (r² = 0.568, p < .001) but only the superficial segment of the depth-resolved OCTA scans (r² = 0.539, p < .001).

CONCLUSIONS

OCTA is a non-invasive tool capable of resolving the retinal vasculature in greater detail when compared with FA but detects significantly fewer MAs. Automatic alignment facilitates quantitative comparison of the microvascular features in DR.

Optical Coherence Tomography Angiography Quality Across Three Multicenter Clinical Studies of Diabetic Retinopathy

Purpose

To explore optical coherence tomography angiography (OCTA) quality and associated factors in multicenter clinical studies.

Methods

OCTA scans were obtained from participants with diabetic retinopathy from three DRCR Retina Network clinical studies using the Optovue AngioVue and ZEISS AngioPlex. Macular (3 × 3 mm and 6 × 6 mm) and optic nerve scans were captured. Quality was assessed by the Casey Reading Center. Scans were considered "poor" if the signal strength index (SSI) was less than 55 (AngioVue) or 7 (AngioPlex) or if excess motion, media opacities, beam defocus, incorrect axial position, or other artifacts were present.

Results

Included were 7539 scans from 787 eyes (461 participants). Sixty-one percent of scans were considered "good" (n = 4630). Of the 3 × 3-mm (n = 2294), 6 × 6-mm (n = 2705), and optic nerve scans (n = 2540), 62%, 63%, and 59%, respectively, were good. Differences in percentage of good scans by machine were not identified (61% of 6216 for the AngioVue and 63% of 1323 for the AngioPlex). The primary reason for poor scans was low SSI for the AngioVue (67%) and excess motion for the AngioPlex (47%). Good scans were associated with younger age (60 ± 12 years vs. 65 ± 11 years; P < 0.001), male gender (64% of males had good scans vs. 57% female; P = 0.007), and better visual acuity (ETDRS letter score 86.5 ± 6.4 [approximate Snellen equivalent 20/20] vs. 81.6 ± 9.7 [approximate Snellen equivalent 20/25]; P < 0.001).

Conclusions

Scan quality or analysis must be improved for OCTA metrics to be used as outcomes in future research.

Translational Relevance

Clinicians and researchers should be aware that poor SSI and artifacts are common issues for OCTA images.

Factors Affecting a Short-Term Response to Anti-VEGF Therapy in Diabetic Macular Edema

Diabetic macular edema (DME) is a common cause of visual impairment in patients with diabetes. Although intravitreal anti-vascular endothelial growth factor (VEGF) injections were efficacious in clinical trials, several patients exhibited a poor response. This study aimed to compare clinical features between patients who were susceptible to intravitreal anti-VEGF injections for DME and those who were not. A single-center, retrospective study of 102 such patients was conducted (123 eyes; mean ± standard deviation age, 63.4 ± 10.8 years; 57.8% males). Systemic and ocular data, assessed at baseline and after a month, were compared between good (>20% decrease in central macular thickness (CMT)) and poor (≤20% decrease in CMT) responders using the Mann-Whitney U test/Fisher's exact test. Eighty-one eyes (65.9%) were good responders. The glycosylated hemoglobin level was higher (p = 0.011) in poor (7.5% ± 0.94%) than in good (7.04% ± 1.19%) responders. The foveal avascular zone was larger (p = 0.0003) in poor (0.67 ± 0.33 μm²) than in good (0.47 ± 0.23 μm²) responders. The number of microaneurysms in the pericapillary network was higher (p = 0.0007) in poor (2.7 ± 2.2) than in good (1.4 ± 2.0) responders. Baseline glycemic control and macular ischemia may be associated with the short-term response to intravitreal anti-VEGF injections.

Title: efficacy of intravitreal dexamethasone implant on hard exudate in diabetic macular edema

Background

To investigate the effect of intravitreal dexamethasone implant (DEX implant) on hard exudate (HE) accompanying diabetic macular edema (DME).

Methods

This study was a non-comparative non-randomized 1-year prospective interventional study. Patients with DME and HE were treated using DEX implant two or three times. Color fundus photography and optical coherence tomography (OCT) were performed at every visit. HE area was measured semi-automatically from the fundus photographs.

Results

Thirty-five patients completed the study. Eleven patients (31.4%) received two injections, while the remaining received three times. HE area (primary outcome) significantly decreased from 1.404±2.094 mm2 (baseline) to 0.212±0.592 mm2 (last visit), which was 24% of the baseline HE area (P<0.001). HE1500 (HE within 1500 μm from the fovea) area also decreased significantly from 0.382±0.467 mm2 to 0.066±0.126 mm2 (P<0.001). Furthermore, anaverage best corrected visual acuity (BCVA) improvement of 4.4 Early Treatment Diabetic Retinopathy Study (ETDRS) letters was observed (from 49.9±18.3 to 54.3±20.4 letters) (P= 0.008). Central macular thickness (CMT) decreased from 455.8±23.6 μm to 366.8±31.1 μm (P=0.009). Repetitive measurements for entire study duration was analyzed using generalized estimating equations (GEE), where BCVA was related to age, CMT, and HE1500 area in multivariate analyses.

Conclusion

DEX implant could reduce and suppress HE in DME for one year with two or three injections. And centrally located HE area (HE1500 area) is related to vision.

Trial registration

ClinicalTrials.gov, NCT02399657, Registered 26 March 2015. 

Longitudinal changes in retinal microvasculature after panretinal photocoagulation in diabetic retinopathy using swept-source OCT angiography

This study evaluated quantitative changes in microvascular parameters after panretinal photocoagulation (PRP) in diabetic retinopathy (DR), using swept-source OCT Angiography (SS-OCTA). A total of 27 treatment-naïve eyes were subjected to PRP and followed-up for > 12 months after the procedure. Foveal avascular zone (FAZ) area, macular perfusion density (PD), and vessel length density (VLD) were calculated on a 3 × 3 mm en face OCTA image and nonperfusion area (NPA) was obtained on a 12 × 12 mm en face OCTA image. One month after PRP, PD and VLD of superficial and deep capillary plexus decreased and subsequently, increased progressively across the next 12 months, with statistically significant differences (P = 0.015 and 0.02). Continuous decreasing trends in total NPA values was observed across 12 months after PRP (P = 0.125). A difference in PD of the superficial capillary plexus between baseline and 6 months post PRP, was significantly associated with the progression of DR, 12 months after PRP (OR 0.528; P = 0.025). We found significant longitudinal retinal microvascular changes after PRP in DR. Overall macular perfusion status was impaired and progressively recovered across the next 12 months, compared to the baseline. Additionally, the early treatment responses in PD can predict the long-term outcomes of PDR after PRP.

Detection rate of diabetic macular microaneurysms comparing dye-based angiography and optical coherence tomography angiography

Diabetic maculopathy (DM) is a microvascular dysfunction clinically characterized by microaneurysms (MA) leading to edema and central visual deprivation. This prospective explorative study investigated 27 eyes of 17 patients with DM by fluorescein/indocyanine green angiography (FA/ICGA; SPECTRALIS HRA-OCT, Heidelberg Engineering) and by swept source-optical coherence tomography angiography (SS-OCTA; DRI-OCT Triton Plus, Topcon) to identify clinically relevant MAs. The SS-OCTA cubes were split into the superficial capillary plexus (SCP) and the deep capillary plexus (DCP) according to the automated segmentation. The images of all modalities were superimposed for alignment by an Early Treatment Diabetic Retinopathy Study grid overlay and compared to each other. In total, the mean number of MAs in FA was 33.4 ± 22 (standard deviation) (median 27.5 [q1:21.75;q3:38.25]), in ICGA 24.9 ± 16.9 (17.5 [14;35]), in the SCP 6.5 ± 3.7 (5.5 [3.75;9.25]) and in the DCP 18.1 ± 10.5 (18.5 [10.75;23.5]). Mixed effects models between ICGA and the DCP were borderline significant (p = 0.048; 95% confidence interval 0.21 to 13.49), whereas all other imaging methods differed significantly. Quantitative analysis of MAs in DM showed a plausible agreement between ICGA and the DCP in SS-OCTA. These findings contribute to the imaging methodology in DM.

Evaluation of different Swept'Source optical coherence tomography angiography (SS-OCTA) slabs for the detection of features of diabetic retinopathy

PURPOSE

To compare different Swept-Source optical coherence tomography angiography (SS-OCTA) slabs for the detection of features of diabetic retinopathy (DR), to find the most suitable slab for grading.

METHODS

Retrospective cross-sectional study. Consecutive patients with DR were evaluated using SS-OCTA. The central 12 × 12 mm scan was used to generate the retinal, superficial and deep slab. The grading results of the slabs were then compared to determine if one specific slab is superior to detect respective features.

RESULTS

A total of 348 eyes (190 patients; mean age 58.1 ± 14.5 years) were graded for features of DR. The retinal slab detected most frequently MAs and IRMAs, however with no significant difference compared to the superficial slab (p = 0.93 and p = 0.93, respectively). Small capillary dropout was most frequently found on the superficial slab, but there was no significant difference compared with the retinal (p = 0.78) and deep slab (p = 0.45). The only statistically significant difference was found for large capillary dropout, where the retinal and superficial slab showed a higher detection rate compared with the deep slab (p ≤ 0.0001 and p = 0.001, respectively).

CONCLUSIONS

The superficial and retinal slabs are equally suitable for grading with no statistically significant difference in the detection rate of the diabetic features examined.

Retinal angiographic alteration in diabetic macular edema after dexamethasone implantation: a case report

Here we reported a rare case of the implantation of a dexamethasone intravitreal implant (DEX) in which decreased retinal vessel density (VD) was found by optical coherence tomography angiography (OCTA). A 74-year-old male with diabetes mellitus presented with bilateral macular edema. The best-corrected visual acuity (BCVA) was 0.6 in the right eye. Diabetic macular edema (DME) was diagnosed. A DEX for the right eye was planned, and the preoperative evaluation showed a superficial VD of 48.74 percent, a deep VD of 53.12 percent, and a foveal avascular zone (FAZ) 0.165 mm² in size by OCTA. The BCVA in the right eye recovered to 0.8, and a notably lower superficial VD of 45.97 percent and a deep VD of 45.40 percent were observed with an enlarged FAZ of 0.294 mm² one month postoperatively. Moreover, BCVA in the right eye was maintained at 0.8, while further reductions in both superficial (40.07 percent) and deep (40.91 percent) VD were noted with a FAZ measured at 0.305 mm² two months postoperatively. In conclusion, retinal superficial and deep VD decreased, while the FAZ increased, after the implantation of the DEX in a patient with DME.

Quantitative Comparison Between Optical Coherence Tomography Angiography and Fundus Fluorescein Angiography Images: Effect of Vessel Enhancement

BACKGROUND AND OBJECTIVE

To compare the vascular parameters derived from optical coherence tomography angiography (OCTA) and fundus fluorescein angiography (FFA) images.

PATIENTS AND METHODS

Twenty-two eyes of 22 patients were imaged with OCTA and FFA. FFA images were cropped to the same dimension as OCTA images after registration. Vessel enhancement using a Frangi filter and local fractal analysis was applied to the superficial layer of the OCTA and cropped FFA images. Foveal avascular zone (FAZ) area, vessel density, spacing between large vessels, and spacing between small vessels were quantified.

RESULTS

FAZ area was similar between original OCTA, Frangi-filtered OCTA, and FFA images (P = .32). Actual OCTA images had significantly higher vessel density (35.2% ± 1.45%, P < .001) than Frangi-filtered OCTA images (29.8% ± 0.78%) and Frangi-filtered FFA images (25.5% ± 2.41%). Spacing between large vessels was significantly lower in original OCTA images (31.9% ± 1.47%, P < .001) than Frangi-filtered OCTA images (36.8% ± 1.24%) and Frangi-filtered FFA images (60.1% ± 2.68%). Further, FFA images had significantly lower spacing between small vessels (14.4% ± 0.43%, P < .001) than original OCTA images (32.7% ± 1.03%) and Frangi-filtered OCTA images (33.4% ± 0.81%).

CONCLUSION

FAZ area was similar between OCTA and FFA, independent of vessel enhancement. However, vessel enhancement improved the agreement of vascular parameters between OCTA and FFA images of the same eye. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:e175-e181.].

The diagnostic value of optical coherence tomography angiography in diabetic retinopathy: a systematic review

PURPOSE

Diabetic retinopathy (DR) is one of the leading causes of blindness worldwide. Accurate investigative tools are essential for the early diagnosis and monitoring of the disease. Optical coherence tomography angiography (OCTA) is a recently developed technology that enables visualisation of the retinal microvasculature.

METHODS

A systematic review of the literature was performed to examine the diagnostic use of OCTA in DR to date. Medline, EMBASE, and Cochrane databases were searched to find relevant studies. Sixty-one original studies were selected for the review.

RESULTS AND DISCUSSION

OCTA has demonstrated the ability to identify microvascular features of DR such as microaneurysms, neovascularisation, and capillary non-perfusion. Furthermore, OCTA is enabling quantitative evaluation of the microvasculature of diabetic eyes. It has demonstrated the ability to detect early microvascular changes, in eyes with or without clinically evident DR. It has also been shown to detect progressive changes in the foveal avascular zone, and vascular perfusion density, with worsening severity of disease. It provides three-dimensional visualisation of the individual retinal vascular networks and is thereby enhancing our understanding of the role of the deeper vasculature in the pathogenesis of diabetic retinopathy and maculopathy.

CONCLUSION

However, limitations exist with current OCTA technology, in respect to the small field of view, image quality, projection artefact, and inaccuracies in analysis of the deeper vascular layers. While questions remain regarding its practical applicability in its present form, with continuing development and improvement of the technology, the diagnostic value of OCTA in diabetic retinopathy is likely to become evident.

New insights into diabetic retinopathy by OCT angiography

Diabetic retinopathy (DR) is one of the most common diabetic complications, which has become a leading cause for vision loss, mainly because of macular edema and vitreous hemorrhage. Optical coherence tomography (OCT) angiography is a novel technique to visualize vascular changes including microaneurysm, non-perfusion area, intraretinal microvascular abnormalities, and neovascularization. Recently, it is possible to quantify vascular density, foveal avascular zone area, non-perfusion area objectively using OCT angiography. In addition, OCT angiography also provides an alternative method to evaluate the effect of anti-vascular endothelial growth factor (VEGF) treatments by providing high resolution images of macular microcirculatory abnormalities. Thus OCT angiography is an effective method to investigate the vascular changes of the disease, and can also be potentially applied in the diagnosis, treatment, and follow up of DR.

Clinical applications of optical coherence tomography angiography: What we have learnt in the first 3 years

A review of the literature from 2014 to 2016 was conducted, focusing on the results of optical coherence tomography angiography in different chorioretinal diseases. In only 3 years, optical coherence tomography angiography has been shown to be an effective tool for diagnosing choroidal neovascularization complicating age-related macular degeneration, pathologic myopia, and inflammatory conditions. The technique has sometimes been considered superior to conventional multimodal imaging, for example, in choroidal neovascularization associated with chronic central serous chorioretinopathy or multifocal choroiditis. In retinal vascular diseases, optical coherence tomography angiography has helped to understand the condition described as paracentral acute middle maculopathy and has been considered highly effective for the analysis of retinal vascular macular changes secondary to retinal vein occlusion or macular telangiectasia. Changes in the foveal avascular zone, also reported in diabetic maculopathy, have been shown to occur before any angiographic signs. A reduction in capillary vascular density has been reported in the fovea of eyes with malignant melanoma, but not in eyes with choroidal nevus. However, optical coherence tomography angiography is a recent technique that probably needs refinements and further studies. Nevertheless, the first 3 years of optical coherence tomography angiography use suggest its clinical relevance and useful applications in daily clinical practice.

An Update on Optical Coherence Tomography Angiography in Diabetic Retinopathy

Optical coherence tomography angiography (OCTA) is a novel non-invasive imaging modality for 3-dimensional visualization of retinal and optic nerve capillary networks. In this article, a comprehensive review of relevant original articles in the PubMed database was performed using the search terms "diabetic retinopathy," "diabetic macular edema," "diabetes mellitus," and "optical coherence tomography angiography." OCTA was found to detect microvascular changes early in diabetes mellitus, even before they become clinically evident. Morphological and qualitative assessment of vascular changes can help to determine the pathophysiological processes, activity, treatment, and follow-up of diabetic retinopathy (DR). Vessel density and foveal avascular zone are the most investigated quantified indices shown to be early predictors of DR, correlated to DR severity and visual function, and useful in predicting response to treatment. OCTA has shown to be a promising alternative to fluorescein angiography in the management of DR. Further studies are warranted to determine the role of OCTA in the routine clinical management of DR.