Abstract
The fovea is one of the most studied retinal specializations in vertebrates, which consists of an invagination of the retinal tissue with high packing of cone photoreceptors, leading to high visual resolution. Between species, foveae differ morphologically in the depth and width of the foveal pit and the steepness of the foveal walls, which could influence visual perception. However, there is no standardized methodology to measure the contour of the foveal pit across species. We present here FOVEA, a program for the quantification of foveal parameters (width, depth, slope of foveal pit) using images from histological cross-sections or optical coherence tomography (OCT). FOVEA is based on a new algorithm to detect the inner retina contour based on the color variation of the image. We evaluated FOVEA by comparing the fovea morphology of two Passerine birds based on histological cross-sections and its performance with data from previously published OCT images. FOVEA detected differences between species and its output was not significantly different from previous estimates using OCT software. FOVEA can be used for comparative studies to better understand the evolution of the fovea morphology in vertebrates as well as for diagnostic purposes in veterinary pathology. FOVEA is freely available for academic use and can be downloaded at: http://estebanfj.bio.purdue.edu/fovea.
Highlights
The retina is an intraocular neural tissue where photoreceptor cells capture and convert photons of light into an electrical ‘image’ that is sent to the brain
We measured with FOVEA the width and depth of the human foveal pit from examples of optical coherence tomography (OCT) images published in two different papers (Hammer et al, 2008; Dubis, McAllister & Carroll, 2009)
Moore et al (2012) developed a method to quantify the position of the retinal specialization and variation in cell density across the retina using retinal topographic maps, many of which are available in an online database
Summary
The retina is an intraocular neural tissue where photoreceptor cells capture and convert photons of light into an electrical ‘image’ that is sent to the brain. Retinal specializations are regions within the retina where distinct cell populations or structural modifications enhance visual information gathering (e.g., high visual acuity). One of the most studied retinal specializations is the fovea, which is characterized by a high density of cone photoreceptors and a pitted invagination of the retinal tissue that allows for higher cell packing (Slonaker, 1897; Walls, 1937; Pumphrey, 1948). The density of retinal ganglion cells increases towards the fovea, at the very center of the foveal pit, the ganglion cell density decreases (and in some cases it is practically zero) as the inner retinal layers are displaced by the tissue invagination (Walls, 1937; Pumphrey, 1948).
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