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Visual Neuroscience Lab

Amblyopia Research
Stereopsis in Amblyopic Eyes

To evaluate the ability of children with amblyopia to process different kinds of stereoscopic information.

Motion Perception in Amblyopia

To use behavioural and functional magnetic imaging (fMRI) techniques to examine motion processing in the amblyopic and fellow eyes of children diagnosed with strabismic, anisometropic, or combined amblyopia.

Select Abstracts from Completed Projects

Meier, K., & Giaschi, D. (2017). Unilateral amblyopia affects two eyes: Fellow eye deficits in amblyopia. Investigative Ophthalmology & Vision Science, 58, 1779-1800.

Unilateral amblyopia is a visual disorder that arises after selective disruption of visual input to one eye during critical periods of development. In the clinic, amblyopia is understood as poor visual acuity in an eye that was deprived of pattern vision early in life. By its nature, however, amblyopia has an adverse effect on the development of a binocular visual system and the interactions between signals from two eyes. Visual functions aside from visual acuity are impacted, and many studies have indicated compromised sensitivity in the fellow eye even though it demonstrates normal visual acuity. While these fellow eye deficits have been noted, no overarching theory has been proposed to describe why and under what conditions the fellow eye is impacted by amblyopia. Here, we consider four explanations that may account for decreased fellow eye sensitivity: the fellow eye is adversely impacted by treatment for amblyopia; the maturation of the fellow eye is delayed by amblyopia; fellow eye sensitivity is impacted for visual functions that rely on binocular cortex; and fellow eye deficits reflect an adaptive mechanism that works to equalize the sensitivity of the two eyes. To evaluate these ideas, we describe five visual functions that are commonly reported to be deficient in the amblyopic eye (hyperacuity, contrast sensitivity, spatial integration, global motion, and motion-defined form), and unify the current evidence for fellow eye deficits. Further research targeted at exploring fellow eye deficits in amblyopia will provide us with a broader understanding of normal visual development and how amblyopia impacts the developing visual system.

Meier, K., Sum, B., & Giaschi, D. (2016). Global motion perception in children with amblyopia as a function of spatial and temporal stimulus parameters. Vision Research, 127, 18-27.

Global motion sensitivity in typically developing children depends on the spatial delta (D) x and temporal Dt displacement parameters of the motion stimulus. Specifically, sensitivity for small Dx values matures at a later age, suggesting it may be the most vulnerable to damage by amblyopia. To explore this possibility, we compared motion coherence thresholds of children with amblyopia (7-14years old) to age-matched controls. Three Dx values were used with two Dt values, yielding six conditions covering a range of speeds (0.3-30deg/s). We predicted children with amblyopia would show normal coherence thresholds for the same parameters on which 5-year-olds previously demonstrated mature performance, and elevated coherence thresholds for parameters on which 5-year-olds demonstrated immaturities. Consistent with this, we found that children with amblyopia showed deficits with amblyopic eye viewing compared to controls for small and medium Dx values, regardless of Dt value. The fellow eye showed similar results at the smaller Dt. These results confirm that global motion perception in children with amblyopia is particularly deficient at the finer spatial scales that typically mature later in development. An additional implication is that carefully designed stimuli that are adequately sensitive must be used to assess global motion function in developmental disorders. Stimulus parameters for which performance matures early in life may not reveal global motion perception deficits.

Giaschi, D., Chapman, C., Meier, K., Narasimhan, S., Regan, D. (2015). The effect of occlusion therapy on motion perception deficits in amblyopia.Vision Research, 114, 122-134.

There is growing evidence for deficits in motion perception in amblyopia, but these are rarely assessed clinically. In this prospective study we examined the effect of occlusion therapy on motion-defined form perception and multiple-object tracking. Participants included children (3-10 years old) with unilateral anisometropic and/or strabismic amblyopia who were currently undergoing occlusion therapy and age-matched control children with normal vision. At the start of the study, deficits in motion-defined form perception were present in at least one eye in 69% of the children with amblyopia. These deficits were still present at the end of the study in 55% of the amblyopia group. For multiple-object tracking, deficits were present initially in 64% and finally in 55% of the children with amblyopia, even after completion of occlusion therapy. Many of these deficits persisted in spite of an improvement in amblyopic eye visual acuity in response to occlusion therapy. The prevalence of motion perception deficits in amblyopia as well as their resistance to occlusion therapy, support the need for new approaches to amblyopia treatment.

Giaschi, D., Lo, R., Narasimhan, S., Lyons, C. & Wilcox, L.M. (2013) Sparing of coarse stereopsis in stereo deficient children with a history of amblyopia. Journal of Vision, 13(10):17,1-15.

Stereoscopic depth perception may be obtained from small retinal disparities that can be fused for single vision (fine stereopsis), but reliable depth information is also obtained from larger disparities that produce double vision (coarse stereopsis). Here we assess the possibility that the early development of coarse stereopsis makes it resilient to the factors that cause amblyopia by comparing performance in children with a history of strabismic, anisometropic, or aniso-strabismic amblyopia and age-matched controls (512 years). The task was to indicate whether a cartoon character was nearer or farther away than a zero-disparity reference frame. Test disparities were grouped into fine and coarse ranges based on preliminary assessment of diplopia thresholds. In the fine range, accuracy increased with disparity for both groups, but children in the amblyopia group performed significantly worse than children in the control group, particularly when their amblyopia was associated with strabismus. In the coarse range, accuracy was constant across all disparities for both groups although performance appeared to be poorer in the aniso-strabismic group. These results suggest that, under some conditions, stereopsis for large disparities may be spared when stereopsis for small disparities is disrupted by early visual deprivation. This undetected residual binocular function has important clinical implications given recent efforts to improve amblyopia treatment outcomes by employing binocular treatment protocols.

Narasimhan S, Harrison ER, Giaschi DE (2012) Quantitative measurement of interocular suppression in children with amblyopia. Vision Research, 66, 1-10.

In this study we explored the possibility of using a dichoptic global motion technique to measure interocular suppression in children with amblyopia. We compared children (5-16 years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children. Under dichoptic viewing conditions, contrast interference thresholds were determined with a global motion direction-discrimination task. Using virtual reality goggles, high contrast signal dots were presented to the amblyopic eye, while low contrast noise dots were presented to the non-amblyopic fellow eye. The contrast of the noise dots was increased until discrimination of the motion direction of the signal dots reached chance performance. Contrast interference thresholds were significantly lower in the strabismic group than in the anisometropic and control group. Our results suggest that interocular suppression is stronger in strabismic than in anisometropic amblyopia.

Ho CS, Giaschi DE. (2007) Stereopsis-dependent deficits in maximum motion displacement in strabismic and anisometropic amblyopia.. Vision Research, 47, 2778-2785.

Direction discrimination thresholds for maximum motion displacement (D(max)) have been previously reported to be abnormal in amblyopic children [Ho, C. S., Giaschi, D. E., Boden, C., Dougherty, R., Cline, R., & Lyons, C. (2005). Deficient motion perception in the fellow eye of amblyopic children. Vision Research, 45, 1615-1627; Ho, C. S., & Giaschi, D. E. (2006). Deficient maximum motion displacement in amblyopia. Vision Research, 46, 4595-4603]. We looked at D(max) thresholds for random dot kinematograms (RDKs) biased toward low- or high-level motion mechanisms. D(max) is thought to be limited, for high-level motion mechanisms, by the efficiency of object feature tracking and probability of false matches. To reduce the influence of low-level mechanisms, we determined thresholds also for a high-pass filtered version of the RDKs. Performance did not significantly differ between strabismic and anisometropic groups with amblyopia, although both groups performed significantly worse than the age-matched control group. D(max) thresholds were higher for children with poor stereoacuity. This was significant in both anisometropic and strabismic groups, and more robust for high-pass filtered RDKs than for unfiltered RDKs. The results imply that impairment of the extra-striate dorsal stream is a likely part of the neural deficit underlying both strabismic and anisometropic amblyopia. This deficit appears to be more dependent on extent of binocularity than etiology. Our findings suggest a possible relationship between fine stereopsis, coarse stereopsis, and motion correspondence mechanisms.

Wang J, Ho C, Giaschi D. (2007) Deficient motion-defined and texture-defined figure-ground segregation in amblyopic children. Journal of Pediatric Ophthalmology and Strabismus, 44 (6), 363-371.

Purpose: Motion-defined (MD) form deficits have been reported in the fellow eye and the amblyopic eye of children with amblyopia. These findings implicate possible direction-selective motion processing and/or static figure-ground segregation deficits. Recent evidence suggests that deficient MD form perception in the fellow eye of amblyopic children may not be fully accounted for by a general motion processing deficit. This study investigates the contribution of figure-ground segregation deficits to the MD form perception deficits in amblyopia. Methods: Performance in 6 amblyopic children (5 anisometropic, 1 aniso-strabismic) and 32 control children with normal vision were assessed on MD form, texture-defined (TD) form and global motion tasks. Results: Group performance on MD and TD form tasks were significantly worse in amblyopic children than in control children. Group performance on global motion was not significantly different between the two groups. Conclusions: Our present findings suggest faulty figure-ground segregation mechanisms are likely responsible for the observed MD form perception deficits in amblyopia.

Ho C, Paul P, Asirvatham A, Cavanagh P, Cline R, Giaschi D. (2006) Abnormal spatial selection and tracking in children with amblyopia. Vision Research, 46, 3274-3283.

We assessed 13 children with unilateral amblyopia and 24 age-matched controls on one low-level and four high-level motion tasks. Children with amblyopia showed similar performance to controls in both amblyopic and fellow eyes on the low-level coherence task and two high-level tasks: 2-dot apparent motion and visual search for biological motion targets. Performance on a single-object tracking task was depressed in amblyopic eyes. Performance on a multiple-object tracking task was depressed in both amblyopic and fellow eyes. These results suggest a preservation of low-level motion perception in amblyopia, and a deficit in high-level attentive tracking.

Ho C, Giaschi D, Boden C, Dougherty R, Cline R, Lyons C. (2005) Deficient motion perception in the fellow eye of amblyopic children. Vision Research 45, 1615-1627.

The extent of motion processing deficits and M/dorsal pathway involvement in amblyopia is unclear. Fellow eye performance was assessed in amblyopic children for motion-defined (MD) form, global motion, and maximum displacement (Dmax) tasks. Group performance on MD form was significantly worse in amblyopic children than in control children. Global motion deficits were significantly related to residual binocular function. Abnormally elevated Dmax thresholds were most prevalent in children with anisometropia. Our findings from these three uncorrelated tasks implicate involvement of binocular motion-sensitive mechanisms in the neural deficits of amblyopic children with strabismic, anisometropic, and aniso-strabismic etiologies.

Ho C, Giaschi D (2005) Low-level and high-level maximum motion displacement deficits in amblyopic children. Journal of Vision 5(8):292a.

Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed values but are highly dependent on stimulus parameters. Dmax increases with reduced dot probability (Boulton & Baker, 1993; Ramachandran & Anstis, 1983) or increased dot size (Cavanagh et al., 1985; Morgan, 1992). It has been theorized that the increase in Dmax under these conditions might reflect a switch in processing from low-level to high-level motion mechanisms in normal observers (Nishida & Sato, 1995; Sato, 1998). The proposed low-level process is reliant on spatial-frequency-tuned motion detectors and the high-level process is mediated by feature matching mechanisms. To determine whether this “switch” in motion mechanisms is observed in amblyopic individuals, thresholds were obtained in both eyes of 9 children with unilateral amblyopia and 9 controls. Each subject performed the task under three random dot display parameters: 20 min size at 5% density (baseline condition), 20 min size at 0.5% density (reduced probability condition), and 1 deg size at 5% density (increased dot size condition). A significant increase in Dmax was observed for displays with reduced dot probability and increased dot size relative to baseline in both groups. However, on the baseline and reduced dot probability conditions, Dmax was significantly lower in both eyes of the amblyopic group compared to the control group. For the increased dot size condition, Dmax was significantly lower in the amblyopic eye but significantly higher in the fellow eye compared to the control group. Extent of binocularity and subtype of amblyopia were not predictive of abnormal performance in this small sample. The results suggest that amblyopic children show the expected shift from low- to high-level motion mechanisms, but both mechanisms appear to be deficient. Our findings implicate abnormal binocular motion processing mechanisms in the neural deficit underlying amblyopia.



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