Concept: Binocular vision
A 19-year-old man presented with a mass in his right eye that had been present since birth but had gradually increased in size. The mass caused vision defects, mild discomfort on blinking, and the intermittent sensation of the presence of a foreign body.
Stereopsis - 3D vision - has become widely used as a model of perception. However, all our knowledge of possible underlying mechanisms comes almost exclusively from vertebrates. While stereopsis has been demonstrated for one invertebrate, the praying mantis, a lack of techniques to probe invertebrate stereopsis has prevented any further progress for three decades. We therefore developed a stereoscopic display system for insects, using miniature 3D glasses to present separate images to each eye, and tested our ability to deliver stereoscopic illusions to praying mantises. We find that while filtering by circular polarization failed due to excessive crosstalk, “anaglyph” filtering by spectral content clearly succeeded in giving the mantis the illusion of 3D depth. We thus definitively demonstrate stereopsis in mantises and also demonstrate that the anaglyph technique can be effectively used to deliver virtual 3D stimuli to insects. This method opens up broad avenues of research into the parallel evolution of stereoscopic computations and possible new algorithms for depth perception.
A stereoscope displays 2-D images with binocular disparities (stereograms), which fuse to form a 3-D stereoscopic object. But a stereoscopic object creates a conflict between vergence and accommodation. Also, motion in depth of a stereoscopic object simulated solely from change in target vergence produces anomalous motion parallax and anomalous changes in perspective. We describe a new instrument, which overcomes these problems. We call it the dichoptiscope. It resembles a mirror stereoscope, but instead of stereograms, it displays identical 2-D or 3-D physical objects to each eye. When a pair of the physical, monocular objects is fused, they create a dichoptic object that is visually identical to a real object. There is no conflict between vergence and accommodation, and motion parallax is normal. When the monocular objects move in real depth, the dichoptic object also moves in depth. The instrument allows the experimenter to control independently each of several cues to motion in depth. These cues include changes in the size of the images, changes in the vergence of the eyes, changes in binocular disparity within the moving object, and changes in the relative disparity between the moving object and a stationary object.
The ability to estimate the distance of objects from one’s self and from each other is fundamental to a variety of behaviours from grasping objects to navigating. The main cue to distance, stereopsis, relies on the slight offsets between the images derived from our left and right eyes, also termed disparities. Here we ask whether the precision of stereopsis varies with professional experience with precise manual tasks. We measured stereo-acuities of dressmakers and non-dressmakers for both absolute and relative disparities. We used a stereoscope and a computerized test removing monocular cues. We also measured vergence noise and bias using the Nonius line technique. We demonstrate that dressmakers' stereoscopic acuities are better than those of non-dressmakers, for both absolute and relative disparities. In contrast, vergence noise and bias were comparable in the two groups. Two non-exclusive mechanisms may be at the source of the group difference we document: (i) self-selection or the fact that stereo-vision is functionally important to become a dressmaker, and (ii) plasticity, or the fact that training on demanding stereovision tasks improves stereo-acuity.
Strabismus is a common condition with misalignment between two eyes that may lead to decrease of visual acuity, lack of binocularity, and diplopia. It is caused by heterogeneous environmental and genetic risk factors. Our previous research has identified new chromosomal susceptibility loci in 4q28.3 and 7q31.2 regions for comitant strabismus in Japanese families. We conducted a verification study by linkage analysis to narrow the chromosomal loci down to a single gene.
A 42-year-old male electrician presented to the eye clinic with decreasing vision 4 weeks after an electrical burn of 14,000 V to the left shoulder. His vision in both eyes was limited to perception of hand motions, with an intraocular pressure of 14 mm Hg in each eye.
Microglia are the resident immune cells of the brain. Increasingly, they are recognized as important mediators of normal neurophysiology, particularly during early development. Here we demonstrate that microglia are critical for ocular dominance plasticity. During the visual critical period, closure of one eye elicits changes in the structure and function of connections underlying binocular responses of neurons in the visual cortex. We find that microglia respond to monocular deprivation during the critical period, altering their morphology, motility and phagocytic behaviour as well as interactions with synapses. To explore the underlying mechanism, we focused on the P2Y12 purinergic receptor, which is selectively expressed in non-activated microglia and mediates process motility during early injury responses. We find that disrupting this receptor alters the microglial response to monocular deprivation and abrogates ocular dominance plasticity. These results suggest that microglia actively contribute to experience-dependent plasticity in the adolescent brain.
Lesions of the fourth (trochlear) cranial nerve cause vertical or oblique diplopia by impairing the ability of the superior oblique muscle to intort and depress the eye. This binocular diplopia worsens in downgaze and lateral gaze away from the affected eye. Because intorsion is necessary to maintain fusion in ocular counter-roll, this diplopia also worsens with head tilt toward the affected eye.(1,2).
Purpose. Amblyopia is a developmental abnormality of visual cortex characterized by spatial processing deficits. Recently, it has been suggested that temporal processing is also affected1. Here we investigated temporal sensitivity by measuring temporal synchrony sensitivity. Methods. In experiment 1, we used a contrast detection task to compare the detection of a flickering 3Hz Gaussian blob with that of synchrony discrimination for a 180° phase shift. In experiment 2, we measured synchrony thresholds directly by assessing the minimum degree of asynchrony that allowed subjects to discriminate which of 4 high-contrast Gaussian blobs was flickering asynchronously in time (synchrony thresholds). Three temporal frequencies (1, 2, and 3 Hz) and two element separations (1.25° and 5°) were compared. Results. In experiment 1, we found that the amblyopes exhibited a synchrony deficit only for the 1.25 degrees element separation in amblyopic eye. In experiment 2, we also found that the sensitivity for non-strabismic (pure anisometropia) amblyopes was reduced for all three temporal frequencies whereas for strabismic (strabismus and anisometropia) amblyopes it was reduced at 3Hz only, possibly suggesting a different extent of impairment in temporal synchrony for different types of amblyopia. Conclusion. This suggests that amblyopes have a foveal low-level temporal processing deficit that could explain the previously reported deficit for figure-ground discrimination.
BACKGROUND: The purpose of the study was to compare the monocular Humphrey Visual Field (HVF) with the binocular Humphrey Esterman Visual Field (HEVF) for determining whether subjects suffering from glaucoma fulfill the new medical requirements for possession of a Swedish driver’s license. METHODS: HVF SITA Fast 24-2 full threshold (monocularly) and HEVF (binocularly) tests were performed consecutively on the same day on 40 subjects with glaucomatous damage of varying degrees in both eyes. Assessment of results was constituted as either “passing” or “failing” score, according to the new medical requirements put into effect September 1, 2010 by the Swedish Transport Agency. RESULTS: Forty subjects were recruited and participated in the study. Sixteen subjects passed both tests, and sixteen subjects failed both tests. Eight subjects passed the HEFV but failed the HVF. There was a significant difference between HEVF and HVF (chi2, p=0.004). There were no subjects who passed the HVF, but failed the HEVF. CONCLUSIONS: The monocular visual field test (HVF) gave more specific information about the location and depth of the defects, and therefore is the overwhelming method of choice for use in diagnostics. The binocular visual field test (HEVF) seems not be as efficient as the HVF in finding visual field defects in glaucoma patients, and is therefore of doubtful use in evaluating visual capabilities in traffic situations.