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EDITORIAL COMMENTARY
Year : 2015  |  Volume : 8  |  Issue : 3  |  Page : 139-140  

Choroidal imaging: Looking ahead


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 Publication20-Nov-2015

Correspondence Address:
Vikas Khetan
Department of Vitreoretina and Ocular Oncology, Sankara Nethralaya, 18, College Road, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-620X.169898

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How to cite this article:
Chhablani J, Khetan V. Choroidal imaging: Looking ahead. Oman J Ophthalmol 2015;8:139-40

How to cite this URL:
Chhablani J, Khetan V. Choroidal imaging: Looking ahead. Oman J Ophthalmol [serial online] 2015 [cited 2017 Oct 22];8:139-40. Available from: http://www.ojoonline.org/text.asp?2015/8/3/139/169898

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.[1] 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.[2] 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.[3] 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.[4] 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.[5] 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.[6]

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.[7] 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.[8]

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.[9] 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.

 
   References Top

1.
Chhablani J, Barteselli G. Clinical applications of choroidal imaging technologies. Indian J Ophthalmol 2015;63:384-90.  Back to cited text no. 1
[PUBMED]  Medknow Journal  
2.
Spaide RF. The choroid and vision loss. Am J Ophthalmol 2014;158:649-50.  Back to cited text no. 2
    
3.
Spaide RF. Age-related choroidal atrophy. Am J Ophthalmol 2009;147:801-10.  Back to cited text no. 3
    
4.
Lee CS, Woo SJ, Kim YK, Hwang DJ, Kang HM, Kim H, et al. Clinical and spectral-domain optical coherence tomography findings in patients with focal choroidal excavation. Ophthalmology 2014;121:1029-35.  Back to cited text no. 4
    
5.
Imamura Y, Iida T, Maruko I, Zweifel SA, Spaide RF. Enhanced depth imaging optical coherence tomography of the sclera in dome-shaped macula. Am J Ophthalmol 2011;151:297-302.  Back to cited text no. 5
    
6.
Mohler KJ, Draxinger W, Klein T, Kolb JP, Wieser W, Haritoglou C, et al. Combined 60° wide-field choroidal thickness maps and high-definition en face vasculature visualization using swept-source megahertz OCT at 1050 nm. Invest Ophthalmol Vis Sci 2015;56:6284-93.  Back to cited text no. 6
    
7.
Kim DY, Fingler J, Zawadzki RJ, Park SS, Morse LS, Schwartz DM, et al. Optical imaging of the chorioretinal vasculature in the living human eye. Proc Natl Acad Sci U S A 2013;110:14354-9.  Back to cited text no. 7
    
8.
Miura M, Makita S, Iwasaki T, Yasuno Y. Three-dimensional visualization of ocular vascular pathology by optical coherence angiography in vivo. Invest Ophthalmol Vis Sci 2011;52:2689-95.  Back to cited text no. 8
    
9.
Jia Y, Bailey ST, Wilson DJ, Tan O, Klein ML, Flaxel CJ, et al. Quantitative optical coherence tomography angiography of choroidal neovascularization in age-related macular degeneration. Ophthalmology 2014;121:1435-44.  Back to cited text no. 9
    




 

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