Showing papers on "Foveal published in 2011"

Foveal shape and structure in a normal population.

Abstract: Purpose The shape of the human fovea presents important but still poorly characterized variations. In this study, the variability of the shape and structure of normal foveae were examined. Methods In a group of 110 eyes of 57 healthy adults, the shape and structure of the fovea were analyzed by automated segmentation of retinal layer on high-resolution optical coherence tomography scans. In an additional group of 10 normal eyes of 10 patients undergoing fluorescein angiography, the size of the foveal avascular zone (FAZ) was correlated to foveal shape. Results From the thickest to the thinnest fovea, there was a structural continuum ranging from a shallow pit with continuity of the inner nuclear layer (INL) over the center (seven eyes; 6.7%), to a complete separation of inner layers overlying a flat and thinner central outer nuclear layer (ONL; eight eyes; 7.3%). Central foveal thickness correlated inversely to the degree of inner layer separation and to the surface of the FAZ. Conclusions Foveal structure strongly correlates with its neurovascular organization. The findings support a developmental model in which the size of the FAZ determines the extent of centrifugal migration of inner retinal layers, which counteracts in some way the centripetal packing of cone photoreceptors.

Prentice Award Lecture 2010: A case for peripheral optical treatment strategies for myopia

Abstract: It is well established that refractive development is regulated by visual feedback. However, most optical treatment strategies designed to reduce myopia progression have not produced the desired results, primarily because some of our assumptions concerning the operating characteristics of the vision-dependent mechanisms that regulate refractive development have been incorrect. In particular, because of the prominence of central vision in primates, it has generally been assumed that signals from the fovea determine the effects of vision on refractive development. However, experiments in laboratory animals demonstrate that ocular growth and emmetropization are mediated by local retinal mechanisms and that foveal vision is not essential for many vision-dependent aspects of refractive development. However, the peripheral retina, in isolation, can effectively regulate emmetropization and mediate many of the effects of vision on the eye’s refractive status. Moreover, when there are conflicting visual signals between the fovea and the periphery, peripheral vision can dominate refractive development. The overall pattern of results suggests that optical treatment strategies for myopia that take into account the effects of peripheral vision are likely to be more successful than strategies that effectively manipulate only central vision. (Optom Vis Sci 2011;88:1029–1044)

Auditory fovea and Doppler shift compensation: adaptations for flutter detection in echolocating bats using CF-FM signals

Abstract: Rhythmical modulations in insect echoes caused by the moving wings of fluttering insects are behaviourally relevant information for bats emitting CF-FM signals with a high duty cycle. Transmitter and receiver of the echolocation system in flutter detecting foragers are especially adapted for the processing of flutter information. The adaptations of the transmitter are indicated by a flutter induced increase in duty cycle, and by Doppler shift compensation (DSC) that keeps the carrier frequency of the insect echoes near a reference frequency. An adaptation of the receiver is the auditory fovea on the basilar membrane, a highly expanded frequency representation centred to the reference frequency. The afferent projections from the fovea lead to foveal areas with an overrepresentation of sharply tuned neurons with best frequencies near the reference frequency throughout the entire auditory pathway. These foveal neurons are very sensitive to stimuli with natural and simulated flutter information. The frequency range of the foveal areas with their flutter processing neurons overlaps exactly with the frequency range where DS compensating bats most likely receive echoes from fluttering insects. This tight match indicates that auditory fovea and DSC are adaptations for the detection and evaluation of insects flying in clutter.

Understanding clinically undetected macular changes in early retinopathy of prematurity on spectral domain optical coherence tomography.

Abstract: PURPOSE To investigate macular changes in acute retinopathy of prematurity (ROP). METHODS Fifty-four premature infants with ROP and 20 controls underwent routine ROP screening with indirect ophthalmoscopy and imaging. A tabletop spectral domain optical coherence tomography (SD-OCT) scanner (Spectralis; Heidelberg Engineering, Heidelberg, Germany) was converted into a handheld device to image infants in the office sans sedation. RESULTS SD-OCT images were obtained in all infants in the office. On SD-OCT, 23 of 79 eyes (29.1%) with stage 2 ROP showed abnormal foveal changes despite clinically normal foveae. Of the 23 eyes, 2 distinct patterns of foveal involvement were observed: "pattern A," which was characterized by dome-shaped foveal elevation and cystoid spaces with highly reflective intervening vertical septae, and "pattern B," which was characterized by preservation of the foveal depression with fewer intraretinal cystoid spaces. These patterns were seen in 12 (52.2%) and 11 (47.8%) eyes, respectively. All eyes (100%) belonging to stage 1 ROP (27) and the normal group (40) had no abnormal SD-OCT changes. The mean central foveal thickness was 156.9 ± 28.3 μm, 206.5 ± 98.7 μm, and 135.9 ± 17.6 μm for stage 1, 2, and normal eyes, respectively (P < 0.001). Nineteen of the 23 eyes underwent serial imaging at 52 weeks' postmenstrual age (PMA), and all of them revealed normalization of foveal contours at this visit. CONCLUSIONS SD-OCT changes of the macula in mild ROP have not been previously described. Our method reveals that infants may be imaged supine and unanesthetized in the office. We hypothesize that these transient foveal changes at the critical time of fovealization in premature infants may influence their visual acuity in the adult life.

The Functional Significance Of Foveal Abnormalities In Albinism Measured Using Spectral-domain Optical Coherence Tomography

Abstract: PURPOSE The relationship between foveal abnormalities in albinism and best-corrected visual acuity (BCVA) is unclear. High-resolution spectral-domain optical coherence tomography (SD OCT) was used to quantify foveal retinal layer thicknesses and to assess the functional significance of foveal morphologic features in patients with albinism. DESIGN Cross-sectional study. PARTICIPANTS Forty-seven patients with albinism and 20 healthy control volunteers were recruited to the study. METHODS Using high-resolution SD OCT, 7×7×2-mm volumetric scans of the fovea were acquired (3-μm axial resolution). The B scan nearest the center of the fovea was identified using signs of foveal development. The thickness of each retinal layer at the fovea and foveal pit depth were quantified manually using ImageJ software and were compared with BCVA. MAIN OUTCOME MEASURES Total retinal thickness, foveal pit depth, photoreceptor layer thickness, and processing layer thickness in relation to BCVA. RESULTS Total photoreceptor layer thickness at the fovea was correlated highly to BCVA (P = 0.0008; r = -0.501). Of the photoreceptor layers, the outer segment length was correlated most strongly to BCVA (P<0.0001; r = -0.641). In contrast, there was no significant correlation between either total retinal thickness or pit depth and BCVA (P>0.05). This was because of an inverse correlation between total photoreceptor layer thickness and total processing layer thickness (P<0.0001; r = -0.696). CONCLUSIONS Neither the total retinal thickness nor the pit depth are reliable indicators of visual deficit, because patients with similar overall retinal thickness had widely varying foveal morphologic features. In albinism, the size of the photoreceptor outer segment was found to be the strongest predictor of BCVA. These results suggest that detailed SD OCT images of photoreceptor anatomic features provide a useful tool in assessing the visual potential in patients with albinism. FINANCIAL DISCLOSURE(S) The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Method for finding the lateral position of the fovea in an SDOCT image volume

Abstract: Embodiments of the present invention provide methods for finding the lateral position of the fovea in an OCT image volume. In one instance, a cost function is developed whose minimum is located at or near the foveal center. This cost function includes one or more measures of retinal layer thickness and/or measures of distance from blood vessels or a priori locations.

Noninvasive imaging of human foveal capillary network using dual-conjugate adaptive optics.

Abstract: PURPOSE. To demonstrate noninvasive imaging of human foveal capillary networks with a high-resolution, wide-field, dual-conjugate adaptive optics (DCAO) imaging instrument. METHODS. The foveal capillary networks of five healthy subjects with no previous history of ocular or neurologic disease or surgery were imaged with a novel high-resolution, wide-field DCAO instrument. The foveal avascular zone (FAZ) in each image was defined using a manual procedure. An automated algorithm based on publicly available and custom-written software was used to identify vessels and extract morphologic FAZ and vessel parameters. Capillary densities were calculated in two annular regions of interest (ROIs) outside the FAZ (500 mu m and 750 mu m outer radius from the foveal center) and in the superior, inferior, temporal, and nasal quadrants within the two ROIs. RESULTS. Mean FAZ area was 0.302 +/- 0.100 mm(2), and mean capillary density (length/area) in the inner ROI was 38.0 +/- 4.0 mm(-1) and 36.4 +/- 4.0 mm(-1) in the outer ROI. The difference in ROI capillary density was not significant. There was no significant difference in quadrant capillary density within the two ROIs or between quadrants irrespective of ROI. CONCLUSIONS. The authors have demonstrated a technique for noninvasive imaging and semiautomated detection and analysis of foveal capillaries. In comparison with other studies, their method yielded lower capillary densities than histology but similar results to the current clinical gold standard, fluorescein angiography. The increased field of view of the DCAO instrument opens up new possibilities for high-resolution noninvasive clinical imaging of foveal capillaries. (Invest Ophthalmol Vis Sci. 2011;52:2649-2655) DOI:10.1167/iovs.10-6054 (Less)

Parafoveal-on-foveal effects on eye movements during reading

Abstract: Parafoveal-on-foveal effects refer to the possibility that processing of the parafoveal word can influence the fixation durations on the foveal word during reading. In this Chapter, I will review the literature of studies examining this issue. Effects observed in reading-like tasks have been questioned on methodological grounds with regards to the generalisibility to normal reading. The clearest evidence for the existence of parafoveal-on-foveal effects comes from experiments allowing tight control over the stimuli but restricting the observations to fixation locations very close to the parafoveal word, and from corpus studies showing reliable but numerically small effects. I will make the claim that with regards to taking reported parafoveal-on-foveal effects as evidence for parallel lexical processing, the jury is still out. The argument is that as long as parafoveal-on-foveal effects are numerically small and difficult to replicate in a controlled experiment, they can be explained on the basis of mislocated fixations, machine error and binocular disparity. These latter three influences can create apparent parafoveal-on-foveal effects without being linked to parallel lexical processing.

Quantifying target conspicuity in contextual modulation by visual search.

Abstract: Contextual elements can strongly modulate visual performance. For example, performance deteriorates when a vernier is flanked by neighboring lines. On a neural level, such contextual modulation is often explained by local spatial interactions such as lateral inhibition or pooling. However, these mechanisms cannot account for a number of recent results which showed that global rather than local factors play a key role in contextual modulation. On a level of perceptual organization, we proposed that contextual modulation increases when the target groups with the flankers and decreases when the target stands out from the flankers. To quantify this "standing out" in foveal vision, here, we performed both a visual search and a vernier offset discrimination task on the same stimulus configurations. Stimulus configurations yielding short reaction times in visual search yielded good vernier discrimination performance. Stimulus configurations yielding long reaction times yielded weaker discrimination. Hence, vernier offset discrimination is superior for targets that are efficiently searched and vice versa.

Reduced mesopic and photopic foveal contrast sensitivity in glaucoma.

Abstract: Objective To demonstrate differences in foveal constrast sensitivity (CS) between glaucomatous and nonglaucomatous eyes using a simple, rapid computerized test. Methods This study included consecutive patients with glaucoma (35 eyes) and age-matched control participants (23 eyes) with visual acuity of 20/30 or better. Patients with any other ocular disease, including cataract, were excluded. All participants underwent a comprehensive ocular examination, perimetry, and CS. Contrast sensitivity was examined by means of 2 computerized psychophysical tests. The transient method included the presentation of a target in a temporal, 2-alternative, forced-choice procedure, and the static method involved 4 forced-choice procedures. The targets were Gabor patches with spatial frequencies of 1.5 to 9.0 cycles per degree. The tests were conducted under photopic and mesopic conditions. Results Significantly lower foveal CS was found in glaucomatous eyes under photopic and mesopic conditions for all spatial frequencies ( P P P Conclusions The results indicate that foveal CS is impaired in glaucoma despite good visual acuity, suggesting that central visual function damage occurs in glaucoma. The similarity between the 2 methods of testing implies that the static method, being the shorter and easier one, may be used in future research. Further research is necessary to establish a CS testing role in the screening and monitoring of glaucoma.

Effects of foveal ablation on the pattern of peripheral refractive errors in normal and form-deprived infant rhesus monkeys (Macaca mulatta).

Abstract: PURPOSE. The purpose of this study was to determine whether visual signals from the fovea contribute to the changes in the pattern of peripheral refractions associated with form deprivation myopia in monkeys. METHODS. Monocular form-deprivation was produced in 18 rhesus monkeys by securing diffusers in front of their treated eyes between 22 ± 2 and 155 ± 17 days of age. In eight of these form-deprived monkeys, the fovea and most of the perifovea of the treated eye were ablated by laser photocoagulation at the start of the diffuser-rearing period. Each eye's refractive status was measured by retinoscopy along the pupillary axis and at 15° intervals along the horizontal meridian to eccentricities of 45°. Control data were obtained from 12 normal monkeys and five monkeys that had monocular foveal ablations and were subsequently reared with unrestricted vision. RESULTS. Foveal ablation, by itself, did not produce systematic alterations in either the central or peripheral refractive errors of the treated eyes. In addition, foveal ablation did not alter the patterns of peripheral refractions in monkeys with form-deprivation myopia. The patterns of peripheral refractive errors in the two groups of form-deprived monkeys, either with or without foveal ablation, were qualitatively similar (treated eyes: F = 0.31, P = 0.74; anisometropia: F = 0.61, P = 0.59), but significantly different from those found in the normal monkeys (F = 8.46 and 9.38 respectively, P < 0.05). CONCLUSIONS. Central retinal signals do not contribute in an essential way to the alterations in eye shape that occur during the development of vision-induced axial myopia.

The effect of flankers on three tasks in central, peripheral, and amblyopic vision.

Abstract: Using identical stimuli and methods, we assessed the effects of flankers on three different tasks, orientation discrimination, contrast discrimination, and detection, in central, peripheral, and amblyopic vision. The goal was to understand the factors that limit performance of a task in the presence of flankers in each of these visual systems. The results demonstrate that: (1) For unflanked targets, the losses in peripheral and amblyopic vision (relative to the normal fovea) are ordered, with the loss of unflanked contrast discrimination thresholds considerably smaller than those for either detection or orientation discrimination. (2) For flanked targets, in normal foveal vision and anisometropic amblyopia, the critical distance is more or less proportional to the target size, whereas in peripheral and strabismic amblyopic vision, the critical distance shows much less (or no) dependence on target size. (3) For the normal fovea, and anisometropic amblyopia, when the target is large (>≈0.2 deg) the amount of threshold elevation induced by flankers is low, increasing when the target is very small. On the other hand, for the periphery and the amblyopic eyes of most strabismic amblyopes, the elevation is large over the range of sizes tested. (4) In peripheral and strabismic amblyopic vision, remote flankers elevate orientation discrimination and contrast discrimination thresholds but not detection thresholds. Our results show clearly that the effects of flanks depend on both the task and the type of visual system. We conclude that in normal foveal vision and anisometropic amblyopia, the effects of flankers largely reflects a reduction in visibility and may be explained by masking. On the other hand, in peripheral vision and strabismic amblyopia, the effects of flankers on orientation discrimination and to a lesser extent contrast discrimination cannot be explained by simple masking and are due to crowding.

When here becomes there: attentional distribution modulates foveal bias in peripheral localization

Abstract: Much research concerning attention has focused on changes in the perceptual qualities of objects while attentional states were varied. Here, we address a complementary question—namely, how perceived location can be altered by the distribution of sustained attention over the visual field. We also present a new way to assess the effects of distributing spatial attention across the visual field. We measured magnitude judgments relative to an aperture edge to test perceived location across a large range of eccentricities (30°), and manipulated spatial uncertainty in target locations to examine perceived location under three different distributions of spatial attention. Across three experiments, the results showed that changing the distribution of sustained attention significantly alters known foveal biases in peripheral localization.

Foveal cone density shows a rapid postnatal maturation in the marmoset monkey

Abstract: The spatial and temporal pattern of cone packing during marmoset foveal development was explored to understand the variables involved in creating a high acuity area. Retinal ages were between fetal day (Fd) 125 and 6 years. Cone density was determined in wholemounts using a new hexagonal quantification method. Wholemounts were labeled immunocytochemically with rod markers to identify reliably the foveal center. Cones were counted in small windows and density was expressed as cones × 103/mm2 (K). Two weeks before birth (Fd 125-130), cone density had a flat distribution of 20-30 K across the central retina encompassing the fovea. Density began to rise at postnatal day 1 (Pd 1) around, but not in, the foveal center and reached a parafoveal peak of 45-55 K by Pd 10. Between Pd 10 and 33, there was an inversion such that cone density at the foveal center rose rapidly, reaching 283 K by 3 months and 600 K by 5.4 months. Peak foveal density then diminished to 440 K at 6 months and older. Counts done in sections showed the same pattern of low foveal density up to Pd 1, a rapid rise from Pd 30 to 90, followed by a small decrease into adulthood. Increasing foveal cone density was accompanied by 1) a reduction in the amount of Muller cell cytoplasm surrounding each cone, 2) increased stacking of foveal cone nuclei into a mound 6-10 deep, and 3) a progressive narrowing of the rod-free zone surrounding the fovea. Retaining foveal cones in a monolayer precludes final foveal cone densities above 60 K. However, high foveal adult cone density (300 K) can be achieved by having cone nuclei stack into columns and without reducing their nuclear diameter. Marmosets reach adult peak cone density by 3-6 months postnatal, while macaques and humans take much longer. Early weaning and an arboreal environment may require rapid postnatal maturation of the marmoset fovea.

Peripheral refraction profiles in subjects with low foveal refractive errors.

Abstract: Purpose.To study the variability of peripheral refraction in a population of 43 subjects with low foveal refractive errors.Methods.A scan of the refractive error in the vertical pupil meridian of the right eye of 43 subjects (age range, 18 to 80 years, foveal spherical equivalent, <±2.5 diop

Flexibility of foveal attention during ocular pursuit.

Abstract: Smooth pursuit of natural objects requires flexible allocation of attention to inspect features. However, it has been reported that attention is focused at the fovea during pursuit. We ask here if foveal attention is obligatory during pursuit, or if it can be disengaged. Observers tracked a stimulus composed of a central dot surrounded by four others and identified one of the dots when it dimmed. Extinguishing the center dot before the dimming improved task performance, suggesting that attention was released from it. To determine if the center dot automatically usurped attention, we provided the pursuit system with an alternative sensory signal by adding peripheral motion that moved with the stimulus. This also improved identification performance, evidence that a central target does not necessarily require attention during pursuit. Identification performance at the central dot also improved, suggesting that the spatial extent of the background did not attract attention to the periphery; instead, peripheral motion freed pursuit attention from the central dot, affording better identification performance. The results show that attention can be flexibly allocated during pursuit and imply that attention resources for pursuit of small and large objects come from different sources.

Mathematical analysis of specific anatomic foveal configurations predisposing to the formation of macular holes.

Abstract: PURPOSE To mathematically analyze and to clinically describe specific anatomic foveal configurations predisposing to the formation of macular holes in comparison with normal foveal anatomy. METHODS In a retrospective observational case-control series, a total of 3882 optical coherence tomography (OCT) foveal thickness maps were analyzed; 96 foveal maps were identified before the formation of macular holes. Maps were analyzed using several anatomic measurements including: retinal thickness, foveal slope, and length of foveal depression. The mathematical analog of the foveal configuration was analyzed using automated symbolic regression software and the equation to describe the mathematical relationship in a 0.083 fit was derived for premacular hole foveas compared with normal age-matched foveas. RESULTS Premacular hole anatomic configuration was found to be significantly different from normal foveal anatomy for maximal slope (P < 0.05) and for central length of foveal depression (P < 0.05). The mathematical regression function followed a first-order cosine curve of level 12 complexity for normal fovea compared with a complex sine curve of level 30 complexity function for premacular hole fovea. Normal foveas had higher symmetry (0.86 ± 0.1, P = 0.03) along the midline, whereas premacular hole foveas had steeper maximal slopes (40 ± 18°, P = 0.01); 75% of these patients had similar foveal configuration in the fellow eye and 50% developed bilateral macular holes. CONCLUSIONS Premacular hole foveal configurations are significantly different from normal foveal configurations. Suspicious macular configurations are easy to recognize on OCT scans and may allow early diagnosis, follow-up, and better management of macular hole-prone patients.

An ERP Assessment of Hemispheric Projections in Foveal and Extrafoveal Word Recognition

Abstract: Background: The existence and function of unilateral hemispheric projections within foveal vision may substantially affect foveal word recognition. The purpose of this research was to reveal these projections and determine their functionality. Methodology: Single words (and pseudowords) were presented to the left or right of fixation, entirely within either foveal or extrafoveal vision. To maximize the likelihood of unilateral projections for foveal displays, stimuli in foveal vision were presented away from the midline. The processing of stimuli in each location was assessed by combining behavioural measures (reaction times, accuracy) with on-line monitoring of hemispheric activity using event-related potentials recorded over each hemisphere, and carefully-controlled presentation procedures using an eye-tracker linked to a fixation-contingent display. Principal Findings: Event-related potentials 100–150 ms and 150–200 ms after stimulus onset indicated that stimuli in extrafoveal and foveal locations were projected unilaterally to the hemisphere contralateral to the presentation hemifield with no concurrent projection to the ipsilateral hemisphere. These effects were similar for words and pseudowords, suggesting this early division occurred before word recognition. Indeed, event-related potentials revealed differences between words and pseudowords 300–350 ms after stimulus onset, for foveal and extrafoveal locations, indicating that word recognition had now occurred. However, these later event-related potentials also revealed that the hemispheric division observed previously was no longer present for foveal locations but remained for extrafoveal locations. These findings closely matched the behavioural finding that foveal locations produced similar performance each side of fixation but extrafoveal locations produced left-right asymmetries. Conclusions: These findings indicate that an initial division in unilateral hemispheric projections occurs in foveal vision away from the midline but is not apparent, or functional, when foveal word recognition actually occurs. In contrast, the division in unilateral hemispheric projections that occurs in extrafoveal locations is still apparent, and is functional, when extrafoveal word recognition takes place.

Evaluating effects of divided hemispheric processing on word recognition in foveal and extrafoveal displays: the evidence from Arabic.

Abstract: Background Previous studies have claimed that a precise split at the vertical midline of each fovea causes all words to the left and right of fixation to project to the opposite, contralateral hemisphere, and this division in hemispheric processing has considerable consequences for foveal word recognition. However, research in this area is dominated by the use of stimuli from Latinate languages, which may induce specific effects on performance. Consequently, we report two experiments using stimuli from a fundamentally different, non-Latinate language (Arabic) that offers an alternative way of revealing effects of split-foveal processing, if they exist. Methods and Findings Words (and pseudowords) were presented to the left or right of fixation, either close to fixation and entirely within foveal vision, or further from fixation and entirely within extrafoveal vision. Fixation location and stimulus presentations were carefully controlled using an eye-tracker linked to a fixation-contingent display. To assess word recognition, Experiment 1 used the Reicher-Wheeler task and Experiment 2 used the lexical decision task. Results Performance in both experiments indicated a functional division in hemispheric processing for words in extrafoveal locations (in recognition accuracy in Experiment 1 and in reaction times and error rates in Experiment 2) but no such division for words in foveal locations. Conclusions These findings from a non-Latinate language provide new evidence that although a functional division in hemispheric processing exists for word recognition outside the fovea, this division does not extend up to the point of fixation. Some implications for word recognition and reading are discussed.