Foveal

About: Foveal is a research topic. Over the lifetime, 2652 publications have been published within this topic receiving 94120 citations.

Two different populations of Müller cells stabilize the structure of the fovea: an optical coherence tomography study

Abstract: To document with spectral-domain optical coherence tomography the structural stabilization of the fovea and the sealing of outer macular defects by Muller cells. A retrospective case series of 45 eyes of 34 patients is described. In cases of a cystic disruption of the foveola as in macular telangiectasia type 2 and vitreomacular traction, the Muller cell cone provides the structural stability of the fovea. In cases of a detachment or disruption of the Muller cell cone, e.g., in foveal pseudocysts, outer lamellar holes, and degenerative and tractional lamellar holes, Muller cells of the foveal walls may provide the structural stability of the fovea by the formation of a hyperreflective external limiting membrane (ELM) which bridges the holes in the central outer nuclear layer (ONL). Muller cells of the foveal walls and parafovea mediate the regeneration of the foveal architecture in cases of outer lamellar and full-thickness macular holes. The regeneration proceeds by a centripetal displacement of photoreceptor cell somata which closes the holes in the central ONL. The closure may be supported by the formation of a glial tissue band at the ELM which seals the hole. The Muller cell cone provides the foveal stability in cases of a cystic disruption of the foveola. The structural stability of the outer foveal layers is mainly provided by the Muller cells of the foveal walls and parafovea; these cells also mediate the regeneration of the outer fovea in cases of a defect of the central ONL.

Organisation of koniocellular-projecting ganglion cells and diffuse bipolar cells in the primate fovea.

Abstract: The roles of the midget and parasol pathways as the anatomical foundation for high-acuity vision at the fovea are well established. There is also evidence for the presence of other (non-midget, non-parasol) ganglion cell types in the foveal retina, but it is not established whether these cells receive input from cone photoreceptors in the central few degrees of the visual field, i.e. the region most important for conscious visual perception. To address this question, we targeted injections of retrograde tracer to the koniocellular layers in the posterior aspect of the lateral geniculate nucleus, where the central visual field is represented, in marmoset monkeys (Callithrix jacchus). Labeled ganglion cells were photofilled to reveal their dendritic morphology. Potential inputs to foveal koniocellular cells from diffuse bipolar cells were investigated in vertical sections through the fovea of marmoset and macaque (Macaca fascicularis) monkey retinas using immunohistochemistry. Forty koniocellular-projecting ganglion cells were analysed. We used an established model of marmoset foveal topography to show that all these koniocellular-projecting cells receive cone inputs from the central-most 6°, with about half the cells receiving input from below 2° eccentricity, in the rod-free central bouquet of cones at the foveola. In addition, all diffuse bipolar types investigated were present in the fovea at stratification depths similar to those of their counterparts in the peripheral retina. We conclude that the diverse visual representations established for koniocellular pathways in the peripheral retina are also a feature of the fovea, suggesting that koniocellular pathways contribute to foveal vision.

Analysis of Parvocellular and Magnocellular Visual Pathways in Human Retina.

Abstract: Two main subcortical pathways serving conscious visual perception are the midget-parvocellular (P), and the parasol-magnocellular (M) pathways. It is generally accepted that the P pathway serves red-green color vision, but the relative contribution of P and M pathways to spatial vision is a long-standing and unresolved issue. Here, we mapped the spatial sampling properties of P and M pathways across the human retina. Data were obtained from immunolabeled vertical sections of six postmortem male and female human donor retinas and imaged using high-resolution microscopy. Cone photoreceptors, OFF-midget bipolar cells (P pathway), OFF-diffuse bipolar (DB) types DB3a and DB3b (M pathway), and ganglion cells were counted along the temporal horizontal meridian, taking foveal spatial distortions (postreceptoral displacements) into account. We found that the density of OFF-midget bipolar and OFF-midget ganglion cells can support one-to-one connections to 1.05-mm (3.6°) eccentricity. One-to-one connections of cones to OFF-midget bipolar cells are present to at least 10-mm (35°) eccentricity. The OFF-midget ganglion cell array acuity is well-matched to photopic spatial acuity measures throughout the central 35°, but the OFF-parasol array acuity is well below photopic spatial acuity, supporting the view that the P pathway underlies high-acuity spatial vision. Outside the fovea, array acuity of both OFF-midget and OFF-DB cells exceeds psychophysical measures of photopic spatial acuity. We conclude that parasol and midget pathway bipolar cells deliver high-acuity spatial signals to the inner plexiform layer, but outside the fovea, this spatial resolution is lost at the level of ganglion cells.SIGNIFICANCE STATEMENT We make accurate maps of the spatial density and distribution of neurons in the human retina to aid in understanding human spatial vision, interpretation of diagnostic tests, and the implementation of therapies for retinal diseases. Here, we map neurons involved with the midget-parvocellular (P pathway) and parasol-magnocellular (M pathway) through human retina. We find that P-type bipolar cells outnumber M-type bipolar cells at all eccentricities. We show that cone photoreceptors and P-type pathway bipolar cells are tightly connected throughout the retina, but that spatial resolution is lost at the level of the ganglion cells. Overall, the results support the view that the P pathway is specialized to serve both high acuity vision and red-green color vision.

Foveal input is not required for perception of crowd facial expression.

Abstract: The visual system extracts average features from groups of objects (Ariely, 2001; Dakin & Watt, 1997; Watamaniuk & Sekuler, 1992), including high-level stimuli such as faces (Haberman & Whitney, 2007, 2009). This phenomenon, known as ensemble perception, implies a covert process, which would not require fixation of individual stimulus elements. However, some evidence suggests that ensemble perception may instead be a process of averaging foveal input across sequential fixations (Ji, Chen, & Fu, 2013; Jung, Bulthoff, Thornton, Lee, & Armann, 2013). To test directly whether foveating objects is necessary, we measured observers' sensitivity to average facial emotion in the absence of foveal input. Subjects viewed arrays of 24 faces, either in the presence or absence of a gaze-contingent foveal occluder, and adjusted a test face to match the average expression of the array. We found no difference in accuracy between the occluded and non-occluded conditions, demonstrating that foveal input is not required for ensemble perception. Unsurprisingly, without foveal input, subjects spent significantly less time directly fixating faces, but this did not translate into any difference in sensitivity to ensemble expression. Next, we varied the number of faces visible from the set to test whether subjects average multiple faces from the crowd. In both conditions, subjects' performance improved as more faces were presented, indicating that subjects integrated information from multiple faces in the display regardless of whether they had access to foveal information. Our results demonstrate that ensemble perception can be a covert process, not requiring access to direct foveal information.