12,13,15ġ) The external limiting membrane band (ELM) is located at the boundary between the cell bodies (nuclei) and the inner segments of the photoreceptors, and comprises clusters of junctional complexes between the Müller cells and the photoreceptors.Ģ) The ellipsoid zone (EZ), which was previously referred as the photoreceptor inner segment/outer segment (IS/OS) junction, is now thought to be formed mainly by mitochondria within the ellipsoid layer of the outer portion of the inner segments of the photoreceptors. 12 The recent nomenclature of the outer retinal bands and their anatomic feature attributions are described below, from the innermost to the outermost ( See Figure 1). 12 The term “zone” was used to define anatomic regions without recognized histopathological correlation to a specific retinal layer. In 2014, an international panel of OCT experts came to a consensus on the most proper terminology for the retinal layers as visualized on OCT, and this terminology is currently commonly used among experts in the field. The following retinal layers are labeled: nerve fiber layer ganglion cell layer inner plexiform layer inner nuclear layer outer plexiform layer outer nuclear layer external limiting membrane ellipsoid zone interdigitation zone and retinal pigment epithelium. Spectral-domain optical coherence tomography image from the macula of a normal eye. These bands have been extensively studied and their identities have been debated in an attempt to establish terminology that could facilitate communication in the field of ophthalmology.įigure 1. 6-8,13-15 This review will cover the most current understanding of the identities of these outer retinal layers, or ORL, and how disruption of these layers on OCT may correlate with visual function.Ĭommercially available SD-OCT instruments have axial resolutions between 4 µm and 7 µm and transverse resolutions of approximately 15 µm, enabling the delineation of four hyper-reflective bands in the outer macula. 12 In particular, the integrity of the photoreceptor layers as visualized using OCT has been demonstrated to have a more robust correlation with visual acuity than retinal thickness measurements alone, which has drawn attention to the continuity of these layers as possible predictive indicators of visual acuity in a wide variety of ophthalmic diseases that affect the macula. 3,4,9-11Īdvances in OCT technology, most importantly the advent of spectral-domain OCT, have enabled retinal images to be acquired at higher speed and resolution, making it easier to identify boundaries between subtle intraretinal layers 2 and details of retinal microstructural changes associated with various retinal conditions. 3-8 Retinal thickness parameters as assessed by OCT have been studied extensively in clinical trials, however only modest correlation between these quantitative parameters and visual acuity among a variety of retinal diseases has been established. 1,2 Since OCT has become available, correlations between anatomy on OCT and visual function have been investigated in a number of retinal diseases. Optical coherence tomography is a well-established diagnostic imaging technique that allows both qualitative (morphology and reflectivity) and quantitative (thickness, mapping and volume) analyses of the retinal architecture.
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