OCT angiography and evaluation of the choroid and choroidal vascular disorders

A Comparison Among Different Automatically Segmented Slabs to Assess Neovascular AMD using Swept Source OCT Angiography

Purpose

We systematically compare the intermodality and interreader agreement in age-related macular degeneration(AMD)-associated neovascularization assessment for optical coherence tomography angiography (OCTA) images obtained using different slabs.

Methods

We collected data from 48 patients (50 eyes) with type 1 or 2 neovascularization (NV) and AMD. Subjects were imaged with a swept source (SS)-OCTA system. For each eye, three OCTA en face images generated from three different slabs were exported: (1) the outer retina to choriocapillaris (ORCC) image, (2) the choriocapillaris (CC) image, and (3) the retinal pigment epithelium (RPE)-RPE fit image. Each image was graded by two readers to assess interreader variability and a single image for each modality was used to assess the intermodality variability.

Results

In the assessment of type 1 NV, mean absolute interreader difference between measured NV areas was 0.19, 0.30, and 0.16 mm² for ORCC, CC, and RPE-RPE fit images, respectively. Similarly, the coefficient of repeatability (CR) and intraclass correlation coefficient (ICC) indicated that the RPE-RPE fit assessment was characterized by the highest interreader reproducibility. Type 1 NV size was 0.58 mm² (0.30–1.60 mm²) on ORCC images, 0.00 mm² (0.00–0.36 mm²) on CC images (P = 0.002 vs. ORCC), and 0.62 mm² (0.31–2.03 mm²) on RPE-RPE fit images (P < 0.0001 vs. CC, P = 0.041 vs. ORCC).

Conclusions

The RPE-RPE fit OCTA images have the highest interreader agreement and deliver larger measurements in type 1 lesions.

Translational Relevance

OCTA imaging may be used in ongoing trials of potential novel treatments for NV.

Pearls and Pitfalls of Optical Coherence Tomography Angiography Imaging: A Review

Optical coherence tomography angiography (OCTA) has significantly expanded our knowledge of the ocular vasculature. Furthermore, this imaging modality has been widely adopted to investigate different ocular and systemic diseases. In this review, a discussion of the fundamental principles of OCTA is followed by the application of this imaging modality to study the retinal and choroidal vessels. A proper comprehension of this imaging modality is essential for the interpretation of OCTA imaging applications in retinal and choroidal disorders.

Choroidal imaging biomarkers

The choroid is the vascular coat of the eye, and its role has been studied in multiple chorioretinal disorders. Recent advancements in choroidal imaging techniques, including enhanced depth imaging optical coherence tomography, swept source optical coherence tomography, en face optical coherence tomography, and optical coherence tomography angiography have facilitated an in-depth analysis of the choroid. The gradual shift from manual to automated segmentation and binarization methods have led to precise and reproducible measurements of choroidal parameters. These qualitative and quantitative parameters, called choroidal imaging biomarkers, have evolved over the past decade from a simple linear subfoveal choroidal thickness to more complex 3D choroidal reconstruction, thus widening the spectrum encompassing multiple parameters. These biomarkers have provided a better understanding of the pathogenesis, are helpful in diagnostic dilemmas, and, in the future may also help to devise treatment options. The lack of normative data, absence of standardized parameters, and limitations of the imaging techniques, however, have led to ambiguity and difficulty in the interpretation of these variables. We attempt to address these lacunae in the literature and provide a basic understanding of the choroid in both health and disease using these choroidal biomarkers.

Topographic distribution of choriocapillaris flow deficits in healthy eyes

Purpose

To evaluate the topographic distribution of the choriocapillaris (CC) flow deficits in a population of healthy subjects.

Methods

Using a swept-source optical-coherence tomography angiography (SS-OCTA) device, two repeated volume 6 x 6 mm and 3 x 3 mm scans were acquired in healthy subjects at the Doheny—UCLA Eye Centers. The en-face CC angiogram was binarized and analyzed for percentage of flow deficits (FD%) using a grid of progressive, concentric rings covering a circular area with a diameter of 2.5 mm (in the 3 x 3 mm scans) and 5 mm (in the 6 x 6 mm scans). The FD% for each ring was plotted against the distance from the fovea. The linear trendline of the resulting curve was analyzed and the slope (m) and intercept (q) were computed.

Results

Seventy-five eyes of 75 subjects were enrolled and divided into three subgroups based on age (year ranges: 21–40, 41–60 and 61–80). For the entire cohort and within each subgroup, there was a significant association between distance from the fovea and FD% in both 3X3 mm and 6X6 mm scans, with flow deficits increasing with closer proximity to the foveal center. Age was a significant predictor for both m and q for both scan patterns, with older subjects showing a steeper slope.

Conclusions

In SS-OCTA images, the topographic distribution of CC flow deficits varies with distance from the fovea and age. In particular, the FD% tends to decrease from the fovea towards the periphery, with a steeper decline with advancing age. These normal trends may need to be accounted for in future studies of the CC in disease.

New concepts in the diagnosis and management of choroidal metastases

The most frequent site of ocular metastasis is the choroid. The occurrence of choroidal metastases has increased steadily due to the longer survival of metastatic patients and the improvement of diagnostic tools. Fundoscopy, ultrasonography, and fluorescein angiography are now complemented by indocyanine green angiography and optical coherence tomography. Choroidal tumor biopsy may also confirm the metastatic nature of the tumor and help to determine the site of the primary malignancy. There is currently no consensus on the treatment strategy. Most patients have a limited life expectancy and for these complex treatments are generally not recommended. However, recent advances in systemic therapy have significantly improved survival of certain patients who may benefit from an aggressive ocular approach that could preserve vision. Although external beam radiation therapy is the most widely used treatment, more advanced forms of radiotherapy that are associated with fewer side effects can be proposed in select cases. In patients with a shorter life expectancy, systemic therapies such as those targeting oncogenic drivers, or immunotherapy can induce a regression of the choroidal metastases, and may be sufficient to temporarily decrease visual symptoms. However, they often acquire resistance to systemic treatment and ocular relapse usually requires radiotherapy for durable control. Less invasive office-based treatments, such as photodynamic therapy and intravitreal injection of anti-VEGF, may also help to preserve vision while reducing time spent in medical settings for patients in palliative care. The aim of this review is to summarize the current knowledge on choroidal metastases, with emphasis on the most recent findings in epidemiology, pathogenesis, diagnosis and treatment.