only focus on thickness maps of 6 or less retinal layers but our new segmentation method is able to segment 12 boundaries (11 layers) in OCT images. In this study, we applied our previously reported 3D intraretinal layer segmentation algorithm (using coarse grained diffusion map) on SD-OCTs and normal thickness maps of 11 intraretinal layers were generated. The normative database for thickness of 3 intraretinal layers, 6 intraretinal layers, and choroidal thickness was also reported. The normative database for thickness of retina has been established in the macula and ONH regions. There is no doubt that it is useful to define a normal standard for thickness profiles which can be helpful for physicians to compare the thickness profiles of each patient with such normal sets and also evaluate progression of certain disease which mostly involve certain retinal layers. There are also some papers emphasizing the importance of evaluating other internal layers of the retina. įurthermore, thickness of retinal nerve fiber layer (RNFL) was of interest for diseases like glaucoma which is expected to change the structure of nerves in retina.
Many researchers focused on segmentation of retina in OCT images to produce the retinal thickness maps and to find a correlation between the quantitative and morphological features of the map and different retinopathies such as glaucoma, multiple sclerosis, and chiasmal compression. Several studies have reported comparisons of total retinal thickness measurements obtained by TD and SD-OCT instruments. According to the selection of different OCT systems for diagnosis, the under-investigation area for thickness analysis may be different but usually around 6 mm × 6 mm region of macula or the optic nerve head (ONH) is selected. Retinal thickness analysis is known to be an important way to quantify pathological changes. Combination of OCT technologies with image processing and segmentation techniques provides useful information about different internal layers of retina to diagnose diseases such as glaucoma and degenerative retinal diseases. Such developments have made OCT one of the fastest adopted technologies in ophthalmology for diagnosis and study of retinal pathologies. The advancement of spectral domain OCT (SD-OCT) over standard time domain optical coherence tomography (TD-OCT) provides higher speed of imaging consequently, less eye motion artifact makes new systems able to generate 3D imaging of retina and two-dimensional thickness maps. Low axial resolution of firstly developed OCTs (15 micrometers) made them less useful in quantitative analysis of retinal layers however, current modalities have an improved axial resolution up to 2 micrometers. Optical coherence tomography (OCT) is a noninvasive imaging technique that enables in vivo cross-sectional visualization of biological tissue at micrometer resolution. Surrounding eight sectors of total retinal thickness and a limited number of sectors in layers 1 and 4 significantly correlated with age. Temporal and inferior quadrants of the total retinal thickness and most of other quadrants of layer 1 were significantly greater in the men than in the women.
Maximum thickness was observed in nasal to the fovea of layer 1 and in a circular pattern in the parafoveal retinal area of layers 2, 3, and 4 and in central foveal area of layer 6. The thickness map of central foveal area in layers 1, 3, and 4 displayed the minimum thickness. The thickness maps are compared among 9 macular sectors within 3 concentric circles as defined by ETDRS. We applied our previously reported 3D intraretinal fast layer segmentation which does not require edge-based image information but rather relies on regional image texture. Mean regional retinal thickness of 11 retinal layers was obtained by automatic three-dimensional diffusion map based method in 112 normal eyes of 76 Iranian subjects. This study was conducted to determine the thickness map of eleven retinal layers in normal subjects by spectral domain optical coherence tomography (SD-OCT) and evaluate their association with sex and age.
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