Binocular Vision Quiz

Visual Direction and Correspondence in Binocular Vision

• Each retinal element has its own sense of direction in space, known as retinal local sign.
• Stimulation of the fovea gives rise to the principal visual direction, which is the dominant sense of visual direction.
• Visual localization involves both oculocentric direction (with respect to the fovea) and egocentric direction (with respect to the body).
• Visual information from the retina is integrated with eye movement and body position information in the visual cortex.
• Hering's Law of Identical Visual Direction states that stimulating the fovea in each eye gives the same visual directions.
• Binocular viewing results in identical oculocentric directions from both eyes, leading to the concept of the cyclopean eye.
• The cyclopean eye is an imaginary concept helpful in understanding binocular directions, situated between the two eyes.
• Corresponding retinal points, when stimulated, give rise to the same visual direction and are perceived as single, while non-corresponding points cause double vision.
• The longitudinal horopter represents a map of retinal correspondence in binocular visual space, formed by joining corresponding points in space.
• The geometrical horopter assumes perfect symmetry and spherical eyes, forming a circle known as the Vieth-Muller circle.
• Empirical measurements of the horopter using different criteria show that it is not a perfect circle as predicted from the geometric model.
• The horopter is also measured based on the region of single binocular vision and optimal stereoscopic depth judgements, revealing its non-circular nature.

Binocular Vision and Depth Perception

• Panum’s area for foveal vision at 30cm ranges from 7-12 min arc, while in the periphery at 5° it is about 24-30 min arc, reducing physiological diplopia.
• Fusion of images requires similarity between left and right eye images, and oculomotor response is associated with it.
• Binocular rivalry occurs when dissimilar images are fused, resulting in rhythmic alternation of separate images.
• Suppression is an inter-ocular process of inhibition, preventing double vision, occurring in ocular abnormalities like amblyopia or strabismus.
• Saccadic suppression occurs during rapid eye movements, preventing perception of movement.
• The Troxler effect causes suppression in monocular conditions.
• Monocular cues for depth perception include aerial perspective, light and shade, overlap, geometric perspective, interpretation of size, motion parallax, and stereopsis.
• Aerial perspective results from light scatter in the atmosphere, causing distant objects to appear blurred and more blue.
• Light and shade contribute to depth perception based on the distribution of light and shade, affecting the appearance of objects.
• Overlap cues depth perception, with overlapped objects appearing further away.
• Geometric perspective provides a powerful cue for depth sense, with progressively smaller angles giving the appearance of changes in depth.
• Motion parallax, where closer objects move more quickly than further ones, can be a powerful cue to depth perception, especially with head movements.

Testing for Eye Alignment and Depth Perception

• Eye alignment testing includes measuring differential eye alignment, refractive error, and conditions such as amblyopia and strabismus.
• Suppression testing involves methods such as Worth (4-dot) and variants, Thomson chart variant, red/green methods, polarization methods, and mirror-pola tests.
• Bagolini striated lens is used for suppression testing, which involves lenses with small parallel striations engraved on them to assess fusion.
• Perception of depth, known as stereopsis, is measured using tests that create relative retinal disparity, such as contour type tests like Titmus Fly and Wirt circles, and random-dot type tests like Randot, TNO, Frisby, and Lang tests.
• Stereopsis is the binocular perception of relative distances between objects resulting from horizontal retinal disparities between monocular images.
• Stereopsis can be tested using real depth objects, polarising filters, anaglyphs, or random-dot patterns, with varying levels of difficulty.
• The TNO test uses red/green anaglyphic plates to measure stereoacuity, with the latest version having the lowest stereoacuity to 30”, which may be challenging for young children.
• The Frisby test involves real depth elements painted on one surface in squares, with different thickness plates creating different disparities for testing stereopsis.
• The Lang test uses small cylindrical lenses to separate the images to each eye, and it only measures gross levels of stereopsis.
• Questions can be asked via Brightspace discussion board or the chat function on Teams for further clarification on the testing methods.