Binocular vision and space perception
- 1. Simi Afroz Assistant Professor (ADHOC) Department of Optometry School of Allied Health Sciences and Research Sharda University
- 2. We ‘‘see’’with our brain, not with our retina, but the first step in elaboration of information received by the eye takes place in the retina. Without the retina, there is no vision.
- 3. Sensory aspect • Relative localisation • Egocentric localization • Each eye has a straight a head localization centred to fovea.This straight a head localisation from fovea is the primary visual direction. • Common visual direction • Cyclopean eye • Any object imaged on the two primary visual direction are perceived as superimposed and as if in the same line through in reality they are separated in space.
- 4. Common subjective relative visual directions • If the two principal lines of direction intersect at the fixation point, it is said that there is binocular fixation. • If only one principal line of direction goes through the fixation point, fixation is monocular. • All object points that simultaneously stimulatethe two foveae appear in one and the same subjective visual direction. • This direction belongs to both the right and left foveae and therefore is called the common subjective visual direction of the foveae.
- 5. Corresponding points and disparate points • Corresponding retinal elements are those elements of the two retinas that give rise in binocular vision to the localization of sensations in one and the same subjective visual direction. • The existence of corresponding retinal elements with their common relative subjective visual directions is the essence of binocular vision. • All other retinal points in the two eyes, which have a localization relative to its own fovea , will also have to relate to the over lapping points of the other eye.These are called corresponding points. All the other points are called disparate points. • Image on the corresponding point are perceived as binocularly single and image on the disparate point are perceived as binocularly double.
- 7. Horopter • In modern usage it is defined as the locus of all object points that are imaged on corresponding retinal elements at a given fixation distance. • Vieth-Muller circle.VMC, empirical horopter; EH, objective frontoparallel plane;OFPP, fixation point; F,inset, law of inscribed circles. Object P on EH is seen singly, but object PO onVMC elicits double vision because of discrepancies between the empirical and theoreticalhoropter.
- 8. Panum’s area of Binocular Fusion • The statement has been made that object points lying on the horopter are seen singly, whereas points off the horopter are seen double. • Not only is single vision possible in Panum’s area but visual objects are seen stereoscopically, that is, in depth.
- 9. Retino motor value • The appearance of an object in the periphery of the visual field attracts attention, and the eye is turned toward the object so that it may be imaged on the fovea. • The resulting eye movement, also called saccade, is extraordinarily precise. • Corresponding impulses are then sent to the extraocular muscles to perform the necessary ocular rotation, mediated and controlled in a manner discussed. • This function of the retinal elements may becharacterized by saying that they have a retinomotor value. • This retinomotor value of the retinal elements increases from the center toward the periphery. • The retinomotor value of the fovea itself is zero.
- 10. Sensory fusion • The unification of visual excitations from corresponding retinal images into a single visual percept, a single visual image. • For sensory fusion to occur, the images not only must be located on corresponding retinal areas but also must be sufficiently similar in size, brightness, and sharpness.
- 11. Motor fusion • The term motor fusion refers to the ability to align the eyesin such a manner that sensory fusion can be maintained. • Unlike sensory fusion, which occurs between corresponding retinal elements in the fovea and the retinal periphery, motorfusion is the exclusive function of the extra foveal retinal periphery. • No stimulus for motor fusion exists when the images ofa fixated visual object fall on the fovea of eacheye.
- 12. Physiological diplopia • Points which are not lying on the horopter curve are imaged disparately and, with certain qualifications, are seen double. • Physiologic diplopia, a fundamental property of binocular vision. • Physiologic diplopia can be readily demonstrated to anyone with normal binocular vision. • Crossed (heteronymous) diplopia of the object p, closer than the fixation point F, imaged in temporal disparity. • Uncrossed (homonymous) diplopia of the object P, more distant than the fixation point F and imaged in nasal disparity.
- 14. Grades of Binocular Vision There are three grades of binocular vision as given by Worth's classification: Grade I : Simultaneous perception Grade II : Fusion Grade III : Stereopsis
- 17. • The normal fusional range is 35/40 PD base out and 16 PD base in on near reading. • 16PD base out and 8PD base in on distance testing.
- 18. Contd........... – Retinal disparity (Fixation disparity) is the basis of 3 D perception – Stereopsis occurs when • Retinal disparity is large enough to simple fusion but small enough to cause diplopia
- 20. The difference stereopsis • Non corresponding retinal elements are stimulated • Motor system is not required • Without fusion it can not occur • Stereopsis occurs only with horizontal disparity fusion • Corresponding retinal elements are stimulated • Motor system is required • Fusion can occur without stereopsis • Fusion occurs horizontal or vertical corresponding retinal points
- 21. Stereopsis • Stereopsis is defined as the relative ordering of visual objects in depth, that is, in the third dimension.This extraordinarily intriguing quality of the visual system requires a rather detailed analysis. • Stereopsis is a response to disparate stimulation of the retinal elements.
- 22. Monocular clues for depth perception • Relative size • Interposition • Linear perspective • Aerial perspective • Distribution of lights & shadows. • Motion parallax
- 23. Relative size
- 24. Interposition
- 27. Distribution of lights & shadows.
- 28. Motion parallax
- 29. Advantage and disadvatages of BSV
- 30. Advantage of having BSV • Stereopsis • Binocular summation. vision shaper, clearer & more sensitive • Larger field of view. • Spare eye • To over come blind spot scotoma • visual field
- 31. Abnormal binocular vision Confusion AND Diplopia Suppression Eccentric fixation and Abnormal retinal correspondence(ARC) Amblyopia
- 32. Anamolies of binocularity Confusion When squinting occurs the two foveas view two different objects that are physically separated in objective space, and send two different images to a single cortical perceptual area.This leads to confusion. Diplopia When squinting occurs an object in space is perceived by the fovea of one eye and some other extra-foveal point of the other eye, which has a different projection or localization value in space.Thus an object would be localized twice in space causing diplopia.
- 34. Binocular vision Adaptation Sensory adaptation • Suppression • ARC Motor adaptation • Fusion • Head posture • Blind spot mechanism
- 35. Suppression • Cortical mechanism of ignoring the image of one eye from cognisance. • Suppression requires for its development: • Constant Large angle deviation • Usually occurs in early childhood • Types of suppression Facultative • Only under binocular condition • VA is not reduced under binocular condition Obligatory • It effects under monocular condition also. • Results in decrease in visual acuity.
- 36. ARC ( anomalous retinal correspondence) • Establishment of new working relationship between fovea of one eye and extra foveal point of other eye. • The attempt to regain the advantage if binocular vision in spite of having anomaly (squint). • In monocular condition fixation is retained by the fovea. Harmonious ARC • Subjective angle is zero • Objective angle is equal to squint. Unharmonious ARC • Angle of deviation has not been fully accounted for subjective or sensory adjustment. • More physiological test are required example Bagolini’s glasses.
- 37. Fusion Ability of the two eye to check a tendency for squint. As log as the fusion is strong squint remains latent ( hetrophoria). It requires binocular input and covering one eye breaks fusion. Fusional convergence is stronger than fusional divergence. If taxed more than its tolerance than it give rise to asthenopia.
- 38. Head posture • To tackle manifest squint which has variable deviation in different gazes. • It is that position of head by assuming which the eyes are in a position of no deviation or such a small deviation that can be fused. • Components of head posture: • Chin elevation or depression • Face turn to right or left side • Head tilt to right or left shoulder
- 39. Blind spot mechanism • In esotropia of 15degree (25 to 30 prism diopter) the image of that eye falls on the blind spot of the other eye so it does not cause diplopia. • Described by Swan.