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Imaging Choroidal Imaging with Swept Source Optical Coherence Tomography – A Review Katarzyna Piasecka 1 and Zofia Michalewska 1,2 1. Third Municipal Hospital K Jonscher, Lodz, Poland; 2. Ophthalmic Clinic Jasne Blonia, Lodz, Poland Abstract The choroid provides up to 70 % of blood and oxygen to the eye. Pathological changes of this vascular tissue may lead to malnutrition of the retina and therefore be involved in the pathogenesis of numerous retinal disorders. Swept source optical coherence tomography (SS-OCT) is a new development of a non-invasive imaging technique that uses a tunable laser source with a higher wavelength light than conventional spectral domain OCT (SD-OCT). This enables visualisation of tissues below the retinal pigment epithelium. Thanks to SS-OCT’s ultrahigh speed and ultrahigh resolution it is possible to assess choroidal layers as well as to automatically create 3D maps of its thickness and volume. This review is to discuss how SS-OCT has improved our understanding of choroidal anatomy and function in various retinal and chorioretinal diseases. In future, detailed evaluation of choroid may play a crucial role in the diagnosis and management of various retinal diseases. Keywords Swept source OCT, SS-OCT, AMD, macular hole, epiretinal membrane, central serous chorioretinopathy, vitreomacular traction syndrome Disclosure: Katarzyna Piasecka and Zofia Michalewska have no conflicts of interest to declare. No funding was received in the publication of this article. Received: 9 October 2014 Accepted: 7 November 2014 Citation: European Ophthalmic Review, 2014;8(2):132–6 Correspondence: Zofia Michalewska, Ophthalmic Clinic Jasne Blonia, Rojna 90, Lodz, Poland. E: zosia_n@yahoo.com Optical coherence tomography (OCT) has revolutionised eye care and significantly improved our understanding of a number of retinal diseases. 1 This non-invasive imaging technique utilises low-coherence interferometry to create cross-sectional images, measuring backscattered or back-reflected light. The first commercially available devices used time domain modality (TD-OCT) and were designed to visualise the retina at 10  µm resolution. They enabled us to obtain the first in vivo images of epiretinal membranes (ERMs), macular holes (MHs), macular oedema, drusen and other pathologies of the fovea. 2–6 Further rapid development resulted in the higher resolution and greater speed of spectral domain OCT (SD-OCT). 7 The new scanning speed of approximately 50,000 A-scans/second allowed SD-OCT to capture high- density 3D images of the structures of the eye. SD-OCT allowed us to reveal important clinical information in micro scale, as well as revealing the thickness of individual layers of the retina including the retinal nerve fibre layer (RNFL), retinal ganglion cell, plexiform, nuclear and photoreceptor layers by means of segmentation algorithms. The current commercially available SD-OCT devices use light wavelengths in the 800– 870 nm range, which is appropriate for achieving highly detailed images of the retina at 5–6 µm resolution. However, the melanin contained in the retinal pigment epithelium (RPE) is highly scattered and absorbed in this range. 8 This makes it difficult to visualise structures that lay beneath this layer, such as the choroid and choriocapillaris. The choroid, which supplies up to 70 % of blood to the eye, is essential for the retina to function normally. Choroidal abnormalities are strongly involved in the pathogenesis of a number of retinal diseases, such as choroidal neovascularisation, chorioretinal inflammatory diseases, central serous chorioretinopathy and others. Thus, an understanding 132 of uveal anatomy is crucial for better diagnosis and the monitoring of treatment in these complicated eye conditions. This review will discuss the most recent developments in OCT imaging using light wavelengths of 1,000–1,040  nm and how the new ability to penetrate below the RPE can improve our knowledge of choroidal morphology, in healthy and diseased eyes. The Choroid – What We Knew Histopathological studies revealed that choroidal layers include the inner and outer Bruch’s membrane, the choriocapillaris, Sattler’s layer, Haller’s layer, delimited from the sclera by suprachoroidal layer (SCL) (lamina fusca, lamina suprachoroidea). Quantitative and qualitative in vivo assessment of the choroid has interested retina specialists, since its role in various chorioretinal diseases was established. Ex vivo histological studies on the thickness of chorioretinal layers revealed the thickest tissue underlies the macula region, thinning of the choroid as a result of ageing and thickening in the course of different chorioretinal pathologies. 9,10 Due to their poor resolution and repeatability, traditional imaging techniques, such as ultrasonography or magnetic resonance imaging, provide limited insight into the diagnostic possibilities of choroidal abnormalities. 11,12 The analysis of choroidal vasculature by means of Indocyanine green (ICG) angiography allows us to examine blood circulation, from the arteries to the veins. 13 Nevertheless, we were unable to visualise specific layers and it was not possible to take precise thickness or volume measurements. OCT in Choroidal Imaging The first attempts at choroidal imaging were reported using SD-OCT devices. Richard Spaide made the first attempt to visualise choroidal © Touc h ME d ic al ME d ia 2014