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T. Y. Chui, A. Bradley, H. Song, S. A. Burns; Foveal Morphology of the Human Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1108.
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© ARVO (1962-2015); The Authors (2016-present)
To develop methodology to map and develop analytic descriptions of the central retinal layers of emmetropic adults using spectral domain optical coherence tomography (SDOCT).
SDOCT imaging (Spectralis HRA+OCT, Heidelberg Engineering, Heidelberg, Germany) was performed on six emmetropic adults (10 eyes; age range 25-54; refractive error +0.750D to -0.50D, mean -0.18D; VA 20/20 or better). One of the subjects was diagnosed with a capillary supply to the foveola in both eyes (Bradley, 1998). The axial and lateral resolutions of the instrument were approximately 7µm and 14µm respectively. A 15° x15° area scan centered at the fovea was acquired in each subject. There were 73 b-scans in the scanned retina. Each b-scan was composed of 768 equally spaced a-scans. The surface of the retina was analyzed by delineating the first signal from the inner limiting membrane and the RPE layer. Foveal depth contour maps were plotted. Foveal scans were rescaled to radial coordinates and the central topography was fit using Zernike polynomials out to the 8th order. From the fits the foveal pit depth and half width at the half depth of the foveal pit were measured, and the individual variations in foveal topography analyzed.
All foveal depth contour maps show naso-temporal asymmetry with a higher elevation at the nasal retina than that at the temporal retina (2%-13%). The average and standard deviation of foveal pit depth and half width were 137.56µm±15.53 and 868.65µm±75.12 in 8 normal emmetropic eyes respectively. However, the foveal pit depth and half width in the subject with foveola capillaries were significantly reduced (67.49µm±3.84 and 687.52µm±26.80 respectively). In this subject, SDOCT images revealed a normal thickness of the outer nuclear layer but an overall thickening of the retina at the foveal pit due to the ingrowth of the inner retinal layers.
This study provides a technique for providing an analytic fit to the foveal shape, and use these fits to examine differences in foveal structure. The ability of the fitting technique to systematically capture the asymmetry of the foveola beyond 8°, which arises in part from the asymmetry caused by the papillo-macular bundle should allow better estimation of the distribution of cells with variations in pit morphology. Post-receptoral neurons were found at the foveola in the subject with foveal blood vessels. Application of this technique should improve our ability to better understand how other factors such as age, retinal diseases, and refractive error affect foveal topography.
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