No / Amblyopia is the condition in which reduced visual function exists despite full optical correction and an absence of observable ocular pathology. Investigation of the underlying neurology of this condition began in earnest around 40 years ago with the pioneering studies conducted by Hubel and Wiesel. Their early work on the impact of monocular deprivation and strabismus initiated what is now a rapidly developing field of cortical plasticity research. Although the monocular deprivation paradigm originated by Hubel and Wiesel remains a key experimental manipulation in studies of cortical plasticity, somewhat ironically, the neurology underlying the human conditions of strabismus and amblyopia that motivated this early work remains elusive. In this review, the authors combine contemporary research on plasticity and development with data from human and animal investigations of amblyopic populations to assess what is known and to reexamine some of the key assumptions about human amblyopia.

Falls in the elderly are a major cause of mortality and morbidity. Elderly people with visual impairment have been found to be at increased risk of falling, with poor visual acuity in one eye causing greater risk than poor binocular visual acuity. The present study investigated whether monocular refractive blur, at a level typically used for monovision correction, would significantly reduce stereoacuity and consequently affect gait parameters when negotiating a raised surface. Fourteen healthy subjects (25.8 ± 5.6 years) walked up to and on to a raised surface, under four visual conditions; binocular, +2DS blur over their non-dominant eye, +2DS blur over their dominant eye and with their dominant eye occluded. Analysis focussed on foot positioning and toe clearance parameters. Monocular blur had no effect on binocular acuity, but caused a small decline in binocular contrast sensitivity and a large decline in stereoacuity (p < 0.01). Vertical toe clearance increased under monocular blur or occlusion (p < 0.01) with a significantly greater increase under blur of the dominant eye compared with blur of the non-dominant eye (p < 0.01). Increase in toe clearance was facilitated by increasing maximum toe elevation (p < 0.01). Findings indicate that monocular blur at a level typically used for monovision correction significantly reduced stereoacuity and consequently the ability to accurately perceive the height and position of a raised surface placed within the travel path. These findings may help explain why elderly individuals with poor visual acuity in one eye have been found to have an increased risk of falling.

No description available.

Abstract Purpose: Interocular inhibitory interactions appear to underlie the establishment of ocular dominance. The inhibitory effect leads to suppression of the non dominant eye in certain conditions. While these processes are not fully understood, the relative differences in image contrast appear to be fundamental. By titrating the relative contrast presented to each eye, a balance in the relative inhibitory effects of each eye can be defined. This research looked at whether the interocular contrast ratio at perceptual balance could be used as an index of the ocular dominance in binocular normal population, and the suppression typically found in the amblyopic population. Contrast variation was compared to luminance variation as well as the application of neutral density filters. Methods: Balance point measures were obtained by varying the interocular levels of contrast for a global motion task viewed dichoptically. One eye received signal dots moving in a given direction while the other eye received noise dots moving randomly. Subjects were tasked with determining the direction of movement of the signal dots. Balanced dichoptic motion sensitivity was achieved under a specific contrast ratio (or the balance point), depending on the observer’s binocular functions. This test was conducted on a control group (n=23) having normal vision and a strabismic amblyopic group (n=10). In addition, a variation of this test was designed with interocular luminance (rather than interocular contrast) serving as the independent variable was conducted to both the control (n=5) and amblyopic groups (n=8). Concurrent eye tracking measures measured changes in eye alignment at the balance point. Results: Although most normal vision subjects showed a balance point at close to equal levels of contrast between the eyes, a minority of them were significantly imbalanced. The suppression measured in the strabismic amblyopic group was significantly greater than that of the control group. Varying the interocular luminance instead of contrast failed to affect the coherence motion thresholds. Ocular alignment was not changed when the balance point was reached. Conclusion: Consistent with the current model of binocular integration, interocular contrast are uniquely important in establishing sensory dominance and suppression. This suggests that the interocular suppression found in amblyopia could be attenuated by methods that allow the reduction of contrast to the fellow fixing eye. Amblyopia therapy might then be improved where such contrast balancing methods are employed instead of the complete patching of the fellow eye.

No description available.

No description available.

Abstract Purpose: Interocular inhibitory interactions appear to underlie the establishment of ocular dominance. The inhibitory effect leads to suppression of the non dominant eye in certain conditions. While these processes are not fully understood, the relative differences in image contrast appear to be fundamental. By titrating the relative contrast presented to each eye, a balance in the relative inhibitory effects of each eye can be defined. This research looked at whether the interocular contrast ratio at perceptual balance could be used as an index of the ocular dominance in binocular normal population, and the suppression typically found in the amblyopic population. Contrast variation was compared to luminance variation as well as the application of neutral density filters. Methods: Balance point measures were obtained by varying the interocular levels of contrast for a global motion task viewed dichoptically. One eye received signal dots moving in a given direction while the other eye received noise dots moving randomly. Subjects were tasked with determining the direction of movement of the signal dots. Balanced dichoptic motion sensitivity was achieved under a specific contrast ratio (or the balance point), depending on the observer’s binocular functions. This test was conducted on a control group (n=23) having normal vision and a strabismic amblyopic group (n=10). In addition, a variation of this test was designed with interocular luminance (rather than interocular contrast) serving as the independent variable was conducted to both the control (n=5) and amblyopic groups (n=8). Concurrent eye tracking measures measured changes in eye alignment at the balance point. Results: Although most normal vision subjects showed a balance point at close to equal levels of contrast between the eyes, a minority of them were significantly imbalanced. The suppression measured in the strabismic amblyopic group was significantly greater than that of the control group. Varying the interocular luminance instead of contrast failed to affect the coherence motion thresholds. Ocular alignment was not changed when the balance point was reached. Conclusion: Consistent with the current model of binocular integration, interocular contrast are uniquely important in establishing sensory dominance and suppression. This suggests that the interocular suppression found in amblyopia could be attenuated by methods that allow the reduction of contrast to the fellow fixing eye. Amblyopia therapy might then be improved where such contrast balancing methods are employed instead of the complete patching of the fellow eye.

No description available.

Abstract Purpose: It is not clear as to whether sensory dominance is affected by test distance. Jiang et al previously reported that that the sensory dominant eyes may be affected by refractive error; however this study was done at a near distance only (60 cm). In this study, we investigated the effect of two different test distances (near, 60 cm vs distance, 6 meters) on the laterality of ocular dominance. Methods: Ocular sensory dominance was quantified in 60 subjects with a technique that involves the dichoptic presentation of a Mondrian noise and a Gabor patch. The threshold to detect the Gabor patch was measured in the presence of decreasing contrast in the Mondrian stimulus. Each eye was tested 50 times and thresholds from two eyes were compared with t-test. If the difference between the two eyes was significant, a subject was classified as having clear ocular sensory dominance and the eye that had lower thresholds was defined as the dominant one. If difference between the two eyes was not significant, a subject was classified as having unclear ocular sensory dominance. Ocular sensory dominance was measured at two different viewing distances, one for near at 60cm away and the other one for far at 6m away. Results: In 31 subjects (51.7 %), dominant eyes remained the same for near and distance viewing. In 15 (25.0 %) subjects, who showed clear ocular sensory dominance at distance, ocular sensory dominance became unclear at near. In 11 (18.3 %) subjects, that had unclear ocular sensory dominance at distance, showed clear ocular sensory dominance at near. In 3 (5.0 %) subjects, the laterality of the dominant eye switched between far and near distance. Conclusions: The effect of viewing distance on ocular sensory dominance is a continuous spectrum. In majority of the population, ocular sensory dominance is not affected. In 43.3 % of the population, ocular sensory dominance varies between unclear and clear status. Only in very rare cases, laterality of dominant eyes switches between near and distance.

Purpose: It is unknown whether individuals with two balanced eyes show quicker response and lower threshold in fine stereoscopic detection. Previous methods to measure ocular dominance were primarily qualitative, which do not quantify the degree of dominance and show limitation in identifying the dominant eye. In this study, we aimed at quantifying the difference of ocular strength between the two eyes with ocular dominance index (ODI) and studying the association of ocular balance between the two eyes with stereoscopic detection. Methods: Stereoscopic threshold was measured in thirty-three subjects. Stereopsis was measured with random dot stimuli. The minimal detectable disparity (Dmin) and the minimal time needed to acquire the best stereoacuity (Tmin) were quantified. Ocular dominance was measured by a continuous flashing technique with the tested eye viewing a titled Gabor patch increasing in contrast and the fellow non-tested eye viewing a Mondrian noise decreasing in contrast. The log ratio of Mondrian to Gabor’s contrasts was recorded when a subject just detected the tilting direction of the Gabor during each trial. The t-value derived from a t-test of the 50 values obtained in each eye was used to determine a subject’s ODI (ocular dominance index) to quantify the degree of ocular dominance. A subject with ODI ≥ 2 (p < 0.05) was defined to have clear dominance and the eye with larger mean ratio was the dominant eye. Results: The Dmin (55.40 arcsec) in subjects with two balanced eyes were not significantly different from the Dmin (43.29 arcsec) in subjects with clear ocular dominance (p = 0.87). Subjects with two balanced eyes had significantly (p = 0.01) shorter reaction times on average (Tmin = 138.28 msec) compared to subjects with clear dominance (Tmin = 1229.02 msec). Tmin values were highly correlated with ocular dominance (p = 0.0004). Conclusion: Subjects with two relatively balanced eyes take shorter reaction time to achieve optimal level of stereoacuity. Keywords: Ocular Dominance, Local Stereopsis, Binocular, Balanced Eyes, Anisometropia