Background: Understanding the neurophysiological mechanisms of Amblyopia, a neurodevelopmental disorder of the visual cortex, will bring us closer to full recovery. Past findings have been contradictory. Results have shown that despite having severe acuity impairment, amblyopes can nonetheless perceive sharp edges. In this study, we explore the representation of blur through a series of image blur-discrimination and matching tasks, to understand more about the amblyopes’ visual system.

Methods: Monocular image blur-discrimination thresholds were measured in a spatial two-alternative forced-choice procedure whereby subjects had to decide which image was the blurriest. Subjects also had to interocularly match pictures that were identical to those used for the image blur discrimination task. Ten amblyopes, as well as a group of ten controls were under study.

Results: Data on amblyopes and controls will be presented for both experiments. According to previous research that was done on blur-edge discrimination and matching, we predict that subjects’ performance will follow a dipper function, that is, all observers will be better at discriminating between both images when a small amount of blur is applied rather than when the image is either sharp or very blurry. We also predict that amblyopes’ blur discrimination will be noisier, but that they will paradoxically be able to match the sharpness of the images presented in the matching task.

Conclusions: This would confirm our hypothesis about amblyopes’ visual system, that they can represent blur levels defined by spatial frequencies that are beyond their resolution limit, and would also raise interesting questions about the visual system in general regarding the different perceptions driven by images versus edges.

Background: Stereoscopic Vision uses the disparity between the two images received by the two eyes in order to create a tridimensional representation. With this study, we aimed at providing an estimate of binocular vision at a level prior to disparity processing. In particular, we wanted to assess the spatial properties of the visual system for detecting interocular correlations (IOC).

Methods: We developed dichoptic stimuli, made of textures which IOC is sinusoidally modulated at various correlation spatial frequencies. Then, we compared the sensitivity to these stimuli to the sensitivity to analogous stimuli with disparity modulation.

Results: We observed that IOC sensitivity presents a low-pass/band-pass profile and increases as a function of presentation duration and contrast, in a similar way as disparity sensitivity.

Conclusions: IOC sensitivity is weakly—though significantly—correlated with disparity sensitivity in the general population, which suggests that it could provide a marker for binocular vision, prior to disparity processing.

Background: In situations where one eye gives a more blurred input to visual processing than the other, the input from the sharper eye tends to dominate the percept. This phenomenon has clinical relevance for monovision treatment, where the two eyes are corrected separately for different distances. We performed a psychophysical investigation of subjects’ ability to identify which of a set of images was blurred in one eye.

Methods: We tested 17 subjects with normal or corrected-to-normal vision. On each trial, subjects viewed an array of four pictures using a monitor with shutter goggles. In the first experiment, three of the pictures were sharp in both eyes (distractors). The fourth picture was sharp in one eye and blurred by a low-pass filter in the other. Subjects identified that odd-one-out target over many trials with different degrees of blur. In the second experiment the target picture was given the same treatment, but the three non-target pictures were made monocular (sharp in one eye, mean grey in the other).

Results: The results from the first experiment with binocular distractors followed our expectations, with subjects showing better performance at detecting more severe blurs. In the second experiment with monocular distractors, we found large individual differences between our observers. Some performed the same as they did in the first condition, others now found the task impossible, and a few performed worse with severe blurs than they did with slight blurs.

Conclusions: Previous studies have reported individual differences in blur suppression, however this study reveals that these differences may depend on the precise details of the judgements being made.

Background: Patching an eye for a period of 2 hours results in a period of plasticity where inter-ocular balance shifts in favor of the patched eye. Acetylcholine has been shown to improve visual function and augment adult neural plasticity. Here we evaluate whether administering the cholinesterase inhibitor donepezil enhances the magnitude or duration of the patching induced shift in ocular balance.

Methods: We used a double-blind drug treatment design to test the effect of donepezil and patching on the shift in ocular balance. We used a well-known binocular phase combination task to measure ocular balance before and after treatment.

Results: Our results demonstrate that donepezil does not enhance, and may actually reduce the magnitude and duration of the patching-induced shift in ocular balance.

Conclusions: Patching induced adult neural plasticity does not appear to be modulated by the cholinergic system, however, increased dose or longer drug administration periods may yield significant results. Future studies on binocular rivalry are in the pipeline.

Background: Short-term monocular deprivation has been recently shown to temporarily increase the sensitivity of the patched eye. Many studies have patched subjects for an arbitrary period of 2.5 hours, but for no principled reason. Our goal is to show a relationship, if any, between the length of patching duration and the strength of its effect.

Methods: We tested nine subjects with three different patching durations: 1-, 2-, 3-hour. Four of the nine subjects were patched for 5-hour. Monocular deprivation was achieved by the use of a translucent eyepatch. A session included two rounds of baseline testing of interocular eye balance, patching, and post-patching tests. Each post-patching test occurred at 0, 3, 6, 12, 24, 48, 60 and 96 minutes after patching to track the patching effect over time. Every subject performed two sessions per condition.

Results: One-hour patching produced a small shift in ocular dominance. A larger shift occurred from 2-hour patching, but 3-hour patching produced a comparable effect to the one measured after 2-hour patching.

Conclusions: These results show a saturation of the patching effect beyond 2-hour patching. Hence, we believe that 2-hour patching duration is the optimal duration for eye dominance changes induced by monocular deprivation.