Foveal

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

Goal representations dominate superior colliculus activity during extrafoveal tracking.

Abstract: The primate superior colliculus (SC) has long been known to be involved in saccade generation. However, SC neurons also exhibit fixation-related and smooth-pursuit-related activity. A parsimonious explanation for these seemingly disparate findings is that the SC contains a map of behaviorally relevant goal locations, rather than just a motor map for saccades and fixation. This explanation predicts that SC activity should reflect the behavioral goal, even when the behavioral response is not fixation or saccades, and even if the goal does not correspond to a visual stimulus. We tested this prediction by using a tracking task that dissociates the stimulus and goal locations. In this task, monkeys tracked the invisible midpoint between two peripheral bars, such that the visual stimuli were peripheral but the goal was foveal/parafoveal. We recorded from SC neurons representing peripheral locations associated with the stimulus or central locations associated with the goal. Most neurons with peripheral response fields did not respond differently during tracking than during passive viewing of the stimulus under fixation; most neurons with central response fields responded more during tracking than during fixation, despite the lack of a visual stimulus. Moreover, the spatial distribution of activity during tracking was larger than that during fixation or tracking of a foveal stimulus, suggesting that the greater spatial uncertainty about the invisible goal corresponded to more widespread SC activity. These results demonstrate the flexibility with which activity across the SC represents the location, as well as the spatial precision, of behaviorally relevant goals for multiple eye movements.

Relationship between foveal cone structure and clinical measures of visual function in patients with inherited retinal degenerations.

Abstract: PURPOSE. To study the relationship between cone spacing and density and clinical measures of visual function near the fovea. METHODS. High-resolution images of the photoreceptor mosaic were obtained with adaptive optics scanning laser ophthalmoscopy from 26 patients with inherited retinal degenerations. Cone spacing measures were made close to or at the foveal center (mean [SD] eccentricity, 0.02 [0.03] degree; maximum eccentricity, 0.13 degree) and were converted to Z-scores, fraction of cones, and percentage-of-cones-below-average compared with normal values for each location (based on 37 age-similar visually normal eyes). Z-scores and percentage of cones below average were compared with best-corrected visual acuity (VA) and foveal sensitivity. RESULTS. Visual acuity was significantly correlated with cone spacing (Spearman rank correlation q ¼� 0.60, P ¼ 0.003) and was preserved (‡80 letters), despite cone density measures that were 52% below normal. Foveal sensitivity showed significant correlation with cone spacing (q ¼� 0.47, P ¼ 0.017) and remained normal (‡35 decibels), despite density measures that were approximately 52% to 62% below normal. CONCLUSIONS. Cone density was reduced by up to 62% below normal at or near the fovea in eyes with VA and sensitivity that remained within normal limits. Despite a significant correlation with foveal cone spacing, VA and sensitivity are insensitive indicators of the integrity of the foveal cone mosaic. Direct, objective measures of cone structure may be more sensitive indicators of disease severity than VA or foveal sensitivity in eyes with inherited retinal degenerations. (ClinicalTrials.gov number, NCT00254605.)

Position of the fovea centralis with respect to the optic nerve head.

Abstract: Examination of the ocular fundus via indirect ophthalmoscopy gives the clinician an impression of foveal position relative to the nerve head. In some patients, the fovea appears to be in an unusual position (i.e., ectopic): it may appear to be higher or lower than expected, or closer to or farther from the nerve head. There is little published quantitative information on this subject. The purpose of this study was to examine foveal position in a group of normal adult eyes, so that clinicians and other researchers will be able to determine on a more objective basis whether or not a given patient shows foveal ectopia. Using ocular fundus photographs for 446 normal adult eyes, we found the foveal center to be, on average, 6.11 degrees +/- 3.32 degrees below a horizontal line bisecting the nerve head. For a smaller sample of 66 eyes, we found the average distance between the nerve head and foveal centers to be 4.93 +/- 0.33 mm (right eye) and 4.88 +/- 0.36 mm (left eye). Correlations of these data for right and left eyes are also examined. Nerve head data for the group of 66 right eyes were also analyzed to yield dimensions of a best-fitting ellipse: the mean minor axis was 1.75 +/- 0.2 mm; the mean major axis 1.95 +/- 0.2 mm. Ectopia (heterotopia) of the fovea has been found in association with chorioretinitis, fibrous traction bands, and/or colobomas of the choroid and optic nerve (including anomalous insertion of the optic nerve), microcephalus, and microphthalmia. A number of separate cases with anomalous nerve heads and/or foveal positions are discussed in this paper.(ABSTRACT TRUNCATED AT 250 WORDS)