|Year : 2015 | Volume
| Issue : 3 | Page : 139-140
Choroidal imaging: Looking ahead
Jay Chhablani1, Vikas Khetan2
1 Department of Vitreoretina, L. V. Prasad Eye Institute, Hyderabad, Telangana, India
2 Department of Ocular Oncology and Vitreoretina, Sankara Nethralaya, Chennai, Tamil Nadu, India
|Date of Web Publication||20-Nov-2015|
Department of Vitreoretina and Ocular Oncology, Sankara Nethralaya, 18, College Road, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chhablani J, Khetan V. Choroidal imaging: Looking ahead. Oman J Ophthalmol 2015;8:139-40
Since the advent of enhanced depth imaging in 2008, imaging of choroid using spectral domain-optical coherence tomography (SD-OCT) has taken a big leap forward. Differentiation of age-related macular degeneration (AMD) from central serous chorioretinopathy (CSCR) and adult-onset foveomacular vitelliform dystrophy, early diagnosis of fibrovascular pigment epithelium detachments, monitoring the treatment outcome in inflammatory diseases and CSCR, better understanding of high myopes, and detailed evaluation of choroidal masses are few of the advantages which are already incorporated in our clinical practice. Moreover, thinning of the choroid itself could be the cause of vision loss in eyes with or without high myopia. A choroid thinner than 30 µ could be the cause of vision loss up to 3 lines. In spite of variability with age, accommodation, ethnicity, as well as diurnal changes, imaging of the choroid is gradually becoming a necessity in patient care.
Newer entities such as age-related choroidal atrophy are now defined, providing an explanation to vision loss due to generalized choroidal thinning secondary to small choroidal vessel loss. Recently, using enhanced depth imaging, focal choroidal excavation, an intrachoroidal concavity, has been reported. Initially, it was considered as congenital malformation, but recently, it has been reported to be associated with diseases such as CSCR, AMD, polypoidal choroidal vasculopathy, and Vogt Koyanagi Harada syndrome (VKH), probably due to choroidal scarring. However, its pathogenesis and clinical implications are yet to be clarified. Dome-shaped macula is reported in high myopes and was considered to be due to focal change in scleral thickness. However, recently, such features were reported in eyes without high myopia. Not only the chorioretinal disorders, but also the role of choroid is now being evaluated in diseases such as diabetes and other vascular disorders.
Choroidal imaging not only provides quantitative assessment, but also the qualitative nature of choroidal tumors such as the reflectivity and the presence of abnormal intrinsic vessels can also be evaluated. Choroidal vascularity index is a ratio of vascular component and total choroidal area to demonstrate the vascularity of the choroid. Understanding the vascularity of choroid could be useful to comprehend the pathogenesis of diseases such as dry AMD, and monitor treatment of conditions such as CSCR and VKH.
Faster and longer wavelength (1050 nm spectral range) imaging technologies such as swept-source OCT (SS-OCT) is able to acquire images of much deeper part of the eye including lamina cribrosa and sclera. SS-OCT allows individual layer segmentation and imaging of wider area compared to SD-OCT. Peripapillary choroidal evaluation is an important diagnostic tool in glaucoma. SS-OCT also provides automated choroidal volume measurement, which could provide information same as retinal volume measurements in future. Wide field, up to 60°, choroidal vascular patterns, and thickness maps would be helpful to provide global choroidal assessment.
Noninvasive en-face phase-variance OCT (pvOCT) provides high resolution, depth-resolved en-face images of vasculature in different layers of the choroid including the choriocapillaris, Sattler's layer, and Haller's layer. En-face pvOCT reveals small focal areas of choriocapillaris dropout within the region of geographic atrophy, as well as defines small choroidal neovascular membrane (CNV) complex helping for early diagnosis. En-face pvOCT can be integrated without any hardware modification and is not affected by regional vascular leakage, unlike contrast imaging modalities and modifications. Doppler optical coherence angiography provides three-dimensional views of ocular vascular pathology in polypoidal choroidal vasculopathy; however, inability to distinguish the CNV from the retinal and choroidal vasculature and quantification of CNV are the major limitations of this technology.
Recently, OCT angiography with split-spectrum amplitude-decorrelation angiography algorithm, developed by David Huang's group from Oregon, improves signal-to-noise ratio through spectral splitting of the OCT images for better blood flow detection. It provides depth-resolved information and detailed images of CNV in neovascular AMD, especially the ill-defined occult CNV. Quantitative information regarding CNV flow and area can be obtained. This technology may enhance CNV detection, segmentation, and quantification to provide comprehensive information to clinicians and help refine individualized treatment strategies. However, OCT angiography still lacks the information provided by fluorescein angiography such as activity of CNV and the overall dynamic information.
Finally, to bring choroidal information at par with retinal information in clinical practice, automation of these measurements is required. Automated segmentation of choroid is now possible, as recent SS-OCT device by Topcon ® provides automated choroidal volume measurements. However, evaluation of individual choroidal vessel or vessel layer is still at in research phase. Various parameters such as volumetric analysis, vessel diameter, light-dark ratio, vasculature thickness, and ratios of inner (smaller) to outer (larger) choroidal vessels would be available soon for detailed choroidal assessment. Choroidal vessel, especially choriocapillaris evaluation using OCT angiography would be a bigger bounce in posterior segment imaging. Quantification of choroidal damage and more objective assessment would improve the diagnostic abilities as well as monitoring in various chorioretinal disorders.
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