Spatial and Temporal Misperceptions in Amblyopic Vision

To investigate the relationship between the subjectively experienced misperceptions and the objectively determined two-dimensional spatial displacement maps in subjects with strabismic and anisometropic amblyopia. Seventeen experimental subjects were asked to describe and sketch their perception of simple geometric pattern, as perceived through their amblyopic eyes. A subgroup of 15 subjects participated in a psychophysical experiment, in which the two-dimensional displacement maps were determined by asking the subjects to reconstruct, point-by-point, memorized circles of different radii. The results of these displacement maps were related to the clinical characteristics and the perceptual descriptions of the same subjects. Twelve of the 17 investigated subjects experienced spatial distortions; six subjects perceived temporal instabilities, either in addition, or in the absence of spatial distortions. Objectively determined spatial displacement and spatial uncertainty were significantly larger in subjects with a history of strabismus and a deep acuity loss than in subjects with refractive etiology and a mild acuity loss. Subjects experiencing temporal instability showed more spatial uncertainty in the amblyopic eye than did subjects with a stable perception. These results suggest that a history of strabismus and a deep amblyopia are more likely to be associated with temporal misperceptions than a refractive etiology and a mild acuity loss. A temporally unstable perception may be related to a more profound disorganization of the central neural pathways connected to the amblyopic eye.

Most distortion/artifacts in low bit-rate compressed videos are strong and obvious to human eyes, and may even change the spatio-temporal structure of visual objects. Therefore it is important to evaluate the compound perceptual impact of spatial and temporal changes. Recent neurophysiological researches have found that the high-level spatial information (shape and depth, etc.) and temporal information (motion, etc.) are processed separately in two visual pathways in human brains. In this paper, spatial and temporal distortions are evaluated separately in two modules, and are then combined in an integration module. Two subjective viewing experiments are performed. One experiment is to evaluate the subjective quality on temporal distortion only, and second experiment is to evaluate the low bit-rate videos with both spatial and temporal distortions. Experimental results and the associated analysis show that the proposed visual quality metric is in good alignment with human perception

Purpose:To report retinal nerve fiber layer thickness (RNFLT) in eyes with amblyopia compared with contralateral healthy eyes.Methods:In this cross-sectional study, we included patients with anisometropic amblyopia, strabismic amblyopia, and mixed amblyopia. All subjects underwent complete ophthalmic examination, including RNFLT measurement with time-domain OCT (Stratus OCT) and scanning laser polarimeter (GDX VCC). A paired “t” test was used to compare average and quadrant-wise RNFL thickness between the amblyopic and contralateral normal eyes. In addition, an analysis of variance test was used to compare various RNFL thickness parameters between the three groups.Results:A total of 33 eyes of 33 subjects with anisometropic amblyopia, 20 eyes of 20 subjects with strabismic amblyopia, and 38 eyes of 38 subjects with mixed amblyopia were included. In the anisometropic amblyopia group, the average RNFLT in the amblyopic eye was 98.2 mm and 99.8 mm in the fellow normal eye (P = 0.5), the total foveal thickness was 152.82 mm (26.78) in the anisometropic eye and 150.42 mm (23.84) in the fellow eye (P = 0.38). The difference between amblyopic and contralateral normal eye for RNFL and macular parameters was statistically insignificant in all three groups. The RNFL thickness in four quadrants was similar in the amblyopic and non-amblyopic eye between all three groups and statistically non-significant.Conclusion:Our study showed that RNFL thickness was similar in amblyopic and non-amblyopic eyes between all three amblyopia groups.

Liquid crystal displays (LCDs) have appeared in applications ranging from medical equipment to automobiles, gas pumps, laptops, and handheld portable computers. These display components present a cascaded energy attenuator to the battery of the handheld device which is responsible for about half of the energy drain at maximum display intensity. As such, the display components become the main focus of every effort for maximization of embedded system's battery lifetime. This paper proposes an approach for pixel transformation of the displayed image to increase the potential energy saving of the backlight scaling method. The proposed approach takes advantage of human visual system (HVS) characteristics and tries to minimize distortion between the perceived brightness values of the individual pixels in the original image and those of the backlight-scaled image. This is in contrast to previous backlight scaling approaches which simply match the luminance values of the individual pixels in the original and backlight-scaled images. Furthermore, this paper proposes a temporally-aware backlight scaling technique for video streams. The goal is to maximize energy saving in the display system by means of dynamic backlight dimming subject to a video distortion tolerance. The video distortion comprises of: 1) an intra-frame (spatial) distortion component due to frame-sensitive backlight scaling and transmittance function tuning and 2) an inter-frame (temporal) distortion component due to large-step backlight dimming across frames modulated by the psychophysical characteristics of the human visual system. The proposed backlight scaling technique is capable of efficiently computing the flickering effect online and subsequently using a measure of the temporal distortion to appropriately adjust the slack on the intra-frame spatial distortion, thereby, achieving a good balance between the two sources of distortion while maximizing the backlight dimming-driven energy saving in the display system and meeting an overall video quality figure of merit. The proposed dynamic backlight scaling approach is amenable to highly efficient hardware realization and has been implemented on the Apollo Testbed II. Actual current measurements demonstrate the effectiveness of proposed technique compared to the previous backlight dimming techniques, which have ignored the temporal distortion effect

To compare the macular and nerve fiber layer thicknesses as measured by optical coherence tomography (OCT) in amblyopic and fellow eyes. Fifty patients with monocular strabismic (n = 25) or anisometropic (n = 25) amblyopia (best corrected visual acuity (BCVA) ranging from 20/40 to 20/400) were included in a prospective cross-sectional descriptive study. A refractive error more than 5 diopters in either eye or an axial length difference between the eyes of more than 1 mm was excluded in the anisometropic group. In all cases, the thickness of the macular area and the peripapillary nerve fiber layer were measured by OCT in both amblyopic and fellow eyes and compared with each other. The mean age of patients was 10 ± 3.1 years (range: 6 to 18 years) in the anisometropic group and 8.9 ± 3.7 years (range: 6 to 18 years) in the strabismic group. In the anisometropic group, the mean macular thickness was significantly increased in the amblyopic eyes (222.6 ± 47.8 μm) versus the fellow eyes (205.6 ± 33.3 μm) (P = .002), although there was no significant difference observed when comparing with the prepapillary nerve fiber layer (P = .55). There was no significant correlation of above-mentioned matters in the strabismic group (P = .07 and .52). A thicker macula was found in anisometropic amblyopic eyes, but the increase of macular thickness in strabismic amblyopic eyes was not significant. Retinal involvement was not observed in the peripapillary nerve fiber layer of amblyopic eyes.

To elucidate the difference in the pathogenesis between strabismic and anisometropic amblyopia. It was a case-control study.We used psychophysical methods, including grating acuity, edge contrast sensitivity, contrast sensitivity function tests, and examined the visual functions of 150 cases from 8 to 40-year-old. Then we applied the Origin 8.0 software for statistical analysis of experimental data, we did the correlation analysis between the grating acuity, edge contrast sensitivity and optotype acuity, and the similarity comparison of the contrast sensitivity function curve between the strabismic and anisometropic amblyopia. The grating acuity had a strong correlation with optotype acuity, the correlation value was 0.81. The grating acuity of the strabismic group was roughly 15% lower than the whole abnormal population, for any given level of optotype acuity; the edge contrast threshold had a weak correlation with optotype acuity, the correlation value was 0.24. Anisometropia, for a given level of optotype acuity, had edge contrast thresholds that were 15% higher (worse) than the whole population, while strabismic and strabismic-anisometropia had edge contrast thresholds that are 17% lower (better) than the whole population. The CSF of all amblyopic eyes were reduced in comparison with the non-amblyopic eye of the same person, the peak sensitivity shifted toward to the low spatial frequency region, the CS curve was depressed especially in the middle and high spatial frequencies, there were no significant difference, but at low frequency area(1.0 c/d) there were statistically significant between the two types of amblyopia(t = 2.239, P < 0.05). There were differences in the patterns of visual loss between strabismic and anisometropic amblyopic patients.

Background Amblyopic eyes typically exhibit greater lag of accommodation. Whether this improves after amblyopia treatment is inconclusive. The aim of this study is to report post-treatment accommodative response in amblyopia and to investigate if the lag is associated with visual acuity, treatment duration, and amblyopia type. Methods Monocular and binocular accommodative responses were measured using Nott's method of dynamic retinoscopy in amblyopia of anisometropic, strabismic, and combined anisometropic-strabismic types and age-matched controls with normal vision. The results were compared using the nonparametric Wilcoxon signed ranks test. Linear regression analysis was used to examine association of the lag to refractive error, duration of therapy, and visual acuity. Results Mean ± SD age of 46 amblyopic and 20 control subjects were 6.9 ± 1.8 and 6.9 ± 2.2 years, respectively. At the time of the study, 30 amblyopic subjects were receiving patching therapy and ceased in the remainder. In amblyopic eyes, mean ± SD monocular and binocular lags were 1.2 ± 0.6D and 1.0 ± 0.5D (p < 0.001), respectively, compared to 0.6 ± 0.3D and 0.5 ± 0.2D (p < 0.005), respectively, in nonamblyopic eyes and 0.4 ± 0.2D and 0.3 ± 0.2D (p=0.093), respectively, in the controls. By types, the monocular lag was significantly higher than the binocular lag (p=0.001) in mixed amblyopia (p=0.004); they were similar in anisometropic (p=0.283) and strabismic (p=0.743) amblyopia. Monocular lag was significantly correlated to BCVA (r = 0.46; p=0.001) and refraction (r = 0.42; p=0.001) but not to patching duration (r = 0.1; p=0.280). Conclusion Inadequate accommodative response, a higher lag, persists in amblyopic eyes even after the treatment. Impaired accommodative response is partly determined by posttherapy visual acuity. Further studies investigating the effect of accommodative lag on visual recovery and whether optical correction of the deficiency may improve visual outcome of the treatment are recommended.

Studies in nonhuman primates show that monocular visual deprivation starting at different ages has different effects on cells in the parvocellular and magnocellular laminae of the lateral geniculate nucleus. The present study used color and luminance contrast sensitivity (CS) measurements to look for differences in parvocellular- and magnocellular-related visual function in human subjects with strabismic amblyopia. Fifteen subjects with early- and 14 with late-onset strabismic amblyopia and similar ranges of visual acuity were studied, together with 15 subjects with normal vision. Contrast sensitivities were measured to an equiluminant (L-M cone-modulated) grating with slow onset and an achromatic (L+M cone-modulated) 0.8-cpd grating with rapid onset using an adaptive Luminance and color CS were lower in the amblyopic eyes than in the fellow eyes of all amblyopes. For luminance CS, this was due both to an increase in sensitivity of the fellow eye and to a reduction in sensitivity in the amblyopic eye. Color CS was greatly reduced in the amblyopic and fellow eyes of subjects with strabismic amblyopia of early- and late onset compared with subjects with normal vision. The reduction in color CS compared with luminance CS was significantly greater in eyes with late- rather than early-onset amblyopia. Parvocellular and magnocellular function are differentially affected in the amblyopic and fellow eyes of subjects with strabismic amblyopia. The difference is more marked in late-onset amblyopia than in early-onset amblyopia.

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.

The mononuclear spatial judgments made by normal adults are quite accurate and precise. Although relatively little is known about how the spatial sense develops, it is likely that it can be compromised by abnormal visual experience as provided, for example, by strabismus. Previously, we reported that the spatial sense of strabismic amblyopic eyes is distorted, having quantified these distortions as marked inaccuracies in equating spatial extents in the nasal and temporal field and specifying when one target is vertically aligned with another. Distortions--localized "expansions" and "compressions" of spatial values and "bending" of direction lines--characterize the amblyopic eyes of strabismics but not non-squinting anisometropes. Thus, according to our previously published hypothesis, spatial distortions can account for the reduced acuity and abnormal oculomotor behavior of strabismic (but not anisometropic) amblyopic eyes. In the present paper, we provide quantification of another spatial measures--spatial precision--and show that extensive imprecision characterizes the space sense of the strabismic amblyopic eye. We now add spatial imprecision to our original hypothesis as a significant element in accounting for the abnormal sensory and motor behaviors of strabismic amblyopic eyes.

To test the theory of gravity one needs to test, on one hand, how space and time are distorted by matter, and on the other hand, how matter moves in a distorted space–time. Current observations provide tight constraints on the motion of matter, through the so-called redshift-space distortions, but they only provide a measurement of the sum of the spatial and temporal distortions, via gravitational lensing. In this letter, we develop a method to measure the time distortion on its own. We show that the coming generation of galaxy surveys, like the Square Kilometre Array, will allow us to measure the distortion of time with an accuracy of 10–30 per cent. Such a measurement will be essential to test deviations from the ΛCDM model in a fully model-independent way. In particular, it can be used to compare the spatial and temporal distortions of space–time and to unambiguously distinguish between modifications of gravity and dark fifth forces acting on dark matter.

The present study aimed to explore temporal frequency discrimination in amblyopia, and the influence of attentional load on amblyopic temporal cognition. Twenty anisometropic amblyopes, 20 strabismic amblyopes and 20 normal subjects were recruited. A flickering disk was used for visual stimuli. A two-alternative, forced-choice staircase paradigm was used to measure the temporal frequency discrimination thresholds of amblyopic eyes, fellow eyes and normal dominant eyes under reference temporal frequencies of 5, 10 and 20 Hz. The just-noticeable differences data were analyzed statistically. In addition, the temporal frequency discrimination thresholds of the subjects were measured under different conditions of attentional load. The changes in temporal frequency discrimination thresholds were compared between amblyopic and normal eyes when attention was loaded. At the reference temporal frequencies of 5 and 10 Hz, temporal thresholds of amblyopic eyes were significantly increased compared with fellow eyes (P<0.05). Regarding strabismic amblyopia, temporal thresholds of fellow eyes were increased compared with normal eyes (P<0.05). However, no correlation was identified between the temporal-frequency discrimination thresholds and the LogMAR visual acuities in amblyopic eyes. In addition, higher attentional load caused greater changes in temporal thresholds in amblyopic eyes, but the situation was not the same for lower attentional load. In conclusion, in the present study a deficit of temporal frequency discrimination in amblyopic eyes and the fellow eyes of strabismic amblyopes was identified. Furthermore, the influence of attentional load on temporal frequency discrimination in amblyopic eyes was increased compared with normal eyes.

Binocular summation in strabismic amblyopia is typically reported as being absent or greatly reduced in behavioral studies and is thought to be because of a preferential loss of excitatory interactions between the eyes. Here, we studied how excitatory and suppressive interactions contribute to binocular contrast interactions along the visual cortical hierarchy of humans with strabismic and anisometropic amblyopia in both sexes, using source-imaged steady-state visual evoked potentials (SSVEP) over a wide range of relative contrast between the two eyes. Dichoptic parallel grating stimuli modulated at unique temporal frequencies in each eye allowed us to quantify spectral response components associated with monocular inputs (self-terms) and the response components because of interaction of the inputs of the two eyes [intermodulation (IM) terms]. Although anisometropic amblyopes revealed a similar pattern of responses to normal-vision observers, strabismic amblyopes exhibited substantially reduced IM responses across cortical regions of interest (V1, V3a, hV4, hMT+ and lateral occipital cortex), indicating reduced interocular interactions in visual cortex. A contrast gain control model that simultaneously fits self- and IM-term responses within each cortical area revealed different patterns of binocular interactions between individuals with normal and disrupted binocularity. Our model fits show that in strabismic amblyopia, the excitatory contribution to binocular interactions is significantly reduced in both V1 and extra-striate cortex, whereas suppressive contributions remain intact. Our results provide robust electrophysiological evidence supporting the view that disruption of binocular interactions in strabismus or amblyopia is because of preferential loss of excitatory interactions between the eyes.SIGNIFICANCE STATEMENT We studied how excitatory and suppressive interactions contribute to binocular contrast interactions along the visual cortical hierarchy of humans with normal and amblyopic vision, using source-imaged SSVEP and frequency-domain analysis of dichoptic stimuli over a wide range of relative contrast between the two eyes. A dichoptic contrast gain control model was used to characterize these interactions in amblyopia and provided a quantitative comparison to normal vision. Our model fits revealed different patterns of binocular interactions between normal and amblyopic vision. Strabismic amblyopia significantly reduced excitatory contributions to binocular interactions, whereas suppressive contributions remained intact. Our results provide robust evidence supporting the view that the preferential loss of excitatory interactions disrupts binocular interactions in strabismic amblyopia.

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