Recent advances in wide field and ultrawide field optical coherence tomography angiography in retinochoroidal pathologies

Imaging the eye as a window to brain health: frontier approaches and future directions

Recent years have seen significant advances in diagnostic testing of central nervous system (CNS) function and disease. However, there remain challenges in developing a comprehensive suite of non- or minimally invasive assays of neural health and disease progression. Due to the direct connection with the CNS, structural changes in the neural retina, retinal vasculature and morphological changes in retinal immune cells can occur in parallel with disease conditions in the brain. The retina can also, uniquely, be assessed directly and non-invasively. For these reasons, the retina may prove to be an important "window" for revealing and understanding brain disease. In this review, we discuss the gross anatomy of the eye, focusing on the sensory and non-sensory cells of the retina, especially microglia, that lend themselves to diagnosing brain disease by imaging the retina. We include a history of ocular imaging to describe the different imaging approaches undertaken in the past and outline current and emerging technologies including retinal autofluorescence imaging, Raman spectroscopy, and artificial intelligence image analysis. These new technologies show promising potential for retinal imaging to be used as a tool for the diagnosis of brain disorders such as Alzheimer's disease and others and the assessment of treatment success.

112° field of view high-resolution swept-source OCT angiography for rat retinas

This study introduces an ultra-wide field (UWF) and high-resolution swept-source optical coherence tomographic angiography (OCTA) system for rat retinal imaging. Using an asymmetrical optics design, the system achieves unprecedented details of retinal structures and vascular plexuses over a large field of view (112°) in a single-shot acquisition. Views of single-nerve fiber bundles and single capillary vessels are consistently visible over a 112° field of view. The system has a long imaging range and high penetration and allows a full view of vitreous hyaloid vessels, retina, choroid, sclera, and posterior ciliary arteries, down to sub-sclera connective tissues. In a longitudinal study of oxygen-induced retinopathy (OIR) in rats, the system successfully revealed the progression and regression of OIR-related vascular pathologies, such as ischemia, neovascularization, and tortuosity. To our knowledge, this novel UWF-OCT/OCTA prototype designed for rat retinal imaging will be a vital tool for monitoring disease progression and evaluating therapeutic interventions in preclinical models.

Regional assessment of choroidal vascularity index in patients with pre- and early-stage diabetic retinopathy using ultra-wide-field OCTA

Purpose

To characterize the regional variations of choroidal vascularity index (CVI) in patients with diabetes mellitus (DM) using ultra-wide-field optical coherence tomography angiography (UWF-OCTA) and identify their correlations with the onset of diabetic retinopathy (DR).

Methods

This cross-sectional, monocular-sampling study recruited 141 participants from four age-matched groups: no DM (NDM), no DR with early DM (EDM) and late DM (LDM), and mild-moderate non-proliferative diabetic retinopathy (mNPDR). UWF-OCTA was employed for circular scans centered on the fovea. CVI in the central region (0-1 mm) and four quadrants of the concentric rings with different ranges (1-3, 3-6, 6-9, 9-12, 12-15, 15-18 mm) was obtained for analysis together with their demographic and clinical data. The Area under the receiver operating characteristic curve (AUC) was calculated to assess the diagnostic efficacy for mNPDR and compared using the DeLong test.

Results

The average CVI was lower in patients with mNPDR compared to other groups across all regions. Although there was no significant difference in DM duration between the LDM and mNPDR groups, a notable variance in CVI was observed, particularly (p = 0.0004) in the temporal quadrant of the 15-18 mm range (T18). CVI in T18 region was negatively correlated with creatinine levels, while positively correlated with body mass index and estimated glomerular filtration rate (ps < 0.05). The CVI in the T18 region demonstrated superior diagnostic efficacy (AUC = 0.755), and when combined with those in other regions and clinical data, the AUC rose to 0.907, which was significantly better (p = 0.0280) than using clinical data alone.

Conclusion

Reduced CVI was observed in the most peripheral region, highly predictive for mNPDR and associated with the declining renal function, thus enhancing the potential of UWF-OCTA to integrate into DM management and promote early DR screening.

Multimodal Imaging in Retinal Vasculitis

BACKGROUND

Retinal vasculitis is an inflammatory condition that affects the retinal blood vessels.

SUMMARY

It can manifest as an idiopathic disorder or be secondary to various infectious or non-infectious diseases, mimicking syndromes, isolated ocular disorders, or drug-induced reactions. Recognizing its distinctive features is crucial for early diagnosis and accurate treatment. This review aimed to demonstrate the variety of tools available to detect disease activity, assess complications, measure the extent of retinal damage, and guide therapy effectively.

KEY MESSAGE

This review article highlights the use of multimodal imaging in the comprehensive evaluation of retinal vasculitis.

Defocus-induced spatial changes in choroidal thickness of chicks observed by wide-field swept-source OCT

Choroid has been claimed to be of importance during ocular development. However, how the choroid responds spatially to different visual cues has not been fully understood. The aim of this study was to investigate defocus-induced spatial changes in choroidal thickness (ChT) in chicks. Eight 10-day-old chicks were fitted monocularly with -10 D or +10 D lenses (day 0), which were removed seven days later (day 7). The ChT was measured on days 0, 7, 14, and 21 using wide-field swept-source optical coherence tomography (SS-OCT) and analyzed with custom-made software. Comparisons of the ChT in the central (1 mm), paracentral (1-3 mm), and peripheral (3-6 mm) ring areas and the ChT in the superior, inferior, nasal, and temporal regions were conducted. Axial lengths and refractions were also evaluated. In the negative lens group, the global ChT of the treated eyes was significantly less than that of the fellow eyes on day 7 (interocular difference: 179.28 ± 25.94 μm, P = 0.001), but thicker on day 21 (interocular difference: 241.80 ± 57.13 μm, P = 0.024). These changes were more pronounced in the central choroid. The superior-temporal choroid changed more during induction but less during recovery. In the positive lens group, the ChT of both eyes increased on day 7 and decreased on day 21, with most changes occurring in the central region, too. The inferior-nasal choroid of the treated eyes changed more during induction but less during recovery. These results provide evidence for regionally asymmetric characteristics of the choroidal response to visual cues and insights into the underlying mechanisms of emmetropization.

Comparison of Automated Thresholding Algorithms in Optical Coherence Tomography Angiography Image Analysis

(1) Background: Calculation of vessel density in optical coherence tomography angiography (OCTA) images with thresholding algorithms varies in clinical routine. The ability to discriminate healthy from diseased eyes based on perfusion of the posterior pole is critical and may depend on the algorithm applied. This study assessed comparability, reliability, and ability in the discrimination of commonly used automated thresholding algorithms. (2) Methods: Vessel density in full retina and choriocapillaris slabs were calculated with five previously published automated thresholding algorithms (Default, Huang, ISODATA, Mean, and Otsu) for healthy and diseased eyes. The algorithms were investigated with LD-F2-analysis for intra-algorithm reliability, agreement, and the ability to discriminate between physiological and pathological conditions. (3) Results: LD-F2-analyses revealed significant differences in estimated vessel densities for the algorithms (p < 0.001). For full retina and choriocapillaris slabs, intra-algorithm values range from excellent to poor, depending on the applied algorithm; the inter-algorithm agreement was low. Discrimination was good for the full retina slabs, but poor when applied to the choriocapillaris slabs. The Mean algorithm demonstrated an overall good performance. (4) Conclusions: Automated threshold algorithms are not interchangeable. The ability for discrimination depends on the analyzed layer. Concerning the full retina slab, all of the five evaluated automated algorithms had an overall good ability for discrimination. When analyzing the choriocapillaris, it might be useful to consider another algorithm.

Stepwise approach for fundus imaging in the diagnosis and management of posterior uveitis

An array of retinochoroid imaging modalities aid in comprehensive evaluation of the immunopathological changes in the retina and choroid, forming the core component for the diagnosis and management of inflammatory disorders such as uveitis. The recent technological breakthroughs have led to the development of imaging platforms that can evaluate the layers of retina and choroid and the structural and functional alteration in these tissues. Ophthalmologists heavily rely on imaging modalities such as dye-based angiographies (fluorescein angiography and indocyanine green angiography), optical coherence tomography, fundus autofluorescence, as well as dye-less angiography such as optical coherence tomography angiograph,y for establishing a precise diagnosis and understanding the pathophysiology of the diseases. Furthermore, these tools are now being deployed with a 'multimodal' approach for swift and accurate diagnosis. In this comprehensive review, we outline the imaging platforms used for evaluation of posterior uveitis and discuss the organized, algorithmic approach for the assessment of the disorders. Additionally, we provide an insight into disease-specific characteristic pathological changes and the established strategies to rule out disorders with overlapping features on imaging.

Diagnostic accuracy of OCTA and OCT for myopic choroidal neovascularisation: a systematic review and meta-analysis

BACKGROUND/OBJECTIVES

The purpose of this project was to systematically review and meta-analyse studies assessing the diagnostic accuracy of optical coherence tomography angiography (OCTA) and optical coherence tomography (OCT) for myopic choroidal neovascularisation (mCNV). Fluorescein angiography (FA) was accepted as the reference standard.

METHODS

PUBMED and EMBASE were searched from inception to March 2021 for studies evaluating the test accuracy of OCTA and/or OCT for diagnosing mCNV. The Preferred Reporting Items for Systematic Reviews and Meta-analyses of Diagnostic Test Accuracy Studies guideline was followed, and the Grading of Recommendations, Assessment, Development and Evaluation approach was used to frame clinical recommendations. Pooled estimates of test accuracy were obtained using a bivariate model.

RESULTS

Of 410 studies assessed for eligibility, 3 studies were identified that compared OCTA to FA and 3 studies were identified that compared spectral domain (SD) OCT to FA. All studies had at least one major methodological flaw leading to an overall high risk of bias. On meta-analysis, the pooled sensitivity of OCTA was 0.89 (95% CI 0.78-0.94) and pooled specificity was 0.93 (95% CI 0.79-0.98). The pooled sensitivity of SD-OCT was 0.99 (95% CI 0.91-1.00). Due to uncertainty in individual studies, the pooled specificity of SD-OCT could not be estimated.

CONCLUSIONS

OCTA can reliably diagnose mCNV in clinically suspected patients, however, SD-OCT may not reliably establish a positive diagnosis of mCNV. Future large, prospective studies with improvements in conduct and reporting are needed to strengthen these clinical recommendations.

Analysis of White and Dark without Pressure in a Young Myopic Group Based on Ultra-Wide Swept-Source Optical Coherence Tomography Angiography

Purpose: This study aimed to investigate the incidence of white without pressure (WWOP) and dark without pressure (DWOP) in a young myopic group based on multimode imaging and to explore the quantitative changes in DWOP based on ultra-wide swept-source optical coherence tomography angiography (SS-OCTA). Methods: A total of 138 patients with high myopia (SE < −6.00 D) were recruited. Examinations, including indirect ophthalmoscope, ultra-wide color fundus photograph, and ultra-wide SS-OCTA, were conducted for each eye. A total of 50 of the 138 patients were selected for further analysis since their DWOP lesions in SS-OCTA could be well quantified. Results: The incidence rates of WWOP and DWOP in the young myopic group were 35.24% and 29.96%, respectively. The patients with a lower spherical equivalent (SE) showed a tendency to have a higher axial length (AL) and higher prevalence of WWOP. Multivariate regression analysis illustrated that a more serious SE and a longer AL were risk factors for both WWOP and DWOP. Eyes with DWOP lesions had lower vessel density (VD) in the whole retina (p < 0.001) and a deep vascular complex (DVC) (p < 0.001), and lower thickness of the outer retina (p < 0.001) compared with healthy counterparts. Conclusion: Ultra-wide SS-OCTA provided new insights into myopic-related peripheral retinal degenerations. DWOP was characterized by thinning of the outer retina and lower perfusion in DVC.

Advances in OCT Imaging in Myopia and Pathologic Myopia

Advances in imaging with optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) technology, including the development of swept source OCT/OCTA, widefield or ultra-widefield systems, have greatly improved the understanding, diagnosis, and treatment of myopia and myopia-related complications. Anterior segment OCT is useful for imaging the anterior segment of myopes, providing the basis for implantable collamer lens optimization, or detecting intraocular lens decentration in high myopic patients. OCT has enhanced imaging of vitreous properties, and measurement of choroidal thickness in myopic eyes. Widefield OCT systems have greatly improved the visualization of peripheral retinal lesions and have enabled the evaluation of wide staphyloma and ocular curvature. Based on OCT imaging, a new classification system and guidelines for the management of myopic traction maculopathy have been proposed; different dome-shaped macula morphologies have been described; and myopia-related abnormalities in the optic nerve and peripapillary region have been demonstrated. OCTA can quantitatively evaluate the retinal microvasculature and choriocapillaris, which is useful for the early detection of myopic choroidal neovascularization and the evaluation of anti-vascular endothelial growth factor therapy in these patients. In addition, the application of artificial intelligence in OCT/OCTA imaging in myopia has achieved promising results.

The Next Steps in Ocular Imaging in Uveitis

PURPOSE

To describe the future steps and advances in the field of ocular imaging in uveitis.

METHODS

Narrative review.

RESULTS

There have been numerous advances in the field of imaging in uveitis in the past decade. Advanced techniques of imaging of the vitreous, vitreo-retinal interface, retinochoroid, and the sclera can provide significant information that helps in understanding the disease pathogenesis and manifestations. Imaging also helps in establishing a diagnosis in challenging cases, along with the laboratory and other assays. Notable developments in ocular imaging include wide-field and ultra-wide field imaging (including angiographies), automated quantification of the retinochoroidal vasculature using optical coherence tomography (OCT) and OCT angiography, quantification of vitreous cells, and intraoperative use of imaging in uveitis, among others.

CONCLUSIONS

We have summarized several technological achievements in ocular imaging in the field of uveitis and provided insights into the potential future developments.