TOPIC 1:Understand the development of binocular vision and its advantages Flashcards
Describe the development of normal binocular vision. what is the sequence of development?
newborn:
VA 6/120 (at 1 month)
Postural reflexes are inborn and must be present if BSV is to develop.
No convergence (early sign at 1 month)
6 months:
Binocular conjugate fixation & convergence
(Motor Development)
1 year:
Fusional movements
(Sensory Development)
5year:
Consolidated
(As adult)
Development: Vision > Motor > Sensory (BSV)
Describe the 3 levels of binocular vision from low to high. SFS
- Simultaneous Perception:
-ability to see two images which may be seen as double
-visual cortex perceives separate stimuli to the two eyes at the same time and concerns itself essentially with the absence of suppression
-SIMPLE SENSORY FUSION - fusion:
-ability to fuse (merge) 2 images with some similarities
-proper functioning of motor and sensory system enables integration f info from 2 eyes so that images can be fused
-TRUE FUSION with some amplitude, some effort made to maintain fusion in site of similarities - stereopsis:
-ability to fuse (merge) 2 images with disparity
-2 images fused and blended to produce stereoscopic effect
-involves perpetual synthesis at a higher level
what are the 3 requirements of BV? how do we assess each of them? (AMS)
- Anatomy of the eye–ocular health exam
- Motor system to co-ordinate the movement of two eyes (motor fusion)
Allows for Bifoveal fixation–BV assessment - Sensory system to integrates the corresponding images (sensory fusion)
Normal retinal correspondence is needed–BV assessment
what are the causes for anomalities in the 3 requirements for BV?
anatomy:
can be due to disease, trauma
motor:
-malfunctions of physiology (eg: convergence excess)
-disease (eg: nerve damage)
-trauma
sensory system:
can be due to loss of clarity, aniseikonia, visual pathway or central integration problems.
what are the 5 advantages of BV? (ELBHS)
- An “extra” eye as a spare in case one is damaged/diseased.
Acts as a “spare” or a Plan B - larger FOV: Total binocular field of view is about 170 degree with an overlapping of 120 degree between both eyes.
Because of the overlapping, blind spots are compensated. - binocular summation:
Vision with 2 eyes are sharper, clearer, more sensitive.
Binocular VA > Monocular VA
Binocular CS > Monocular CS - hand-eye coordination: Two eyes will give you better eye hand coordination than using one eye in most of the activities.
- stereopsis: depth perception (main advantage of BV!)
small differences (disparity) between the 2 images seen by 2 eyes add up to a three-dimensional (3D) picture
This is important for:
Figure-ground segregation
Avoiding collisions with looming objects
Navigating our environment
differentiate between simultaneous perception and superimposition
simultaneous perception: -ability to see two images which may be seen as double
superimposition: two diff images are seen simultaneously in the same direction in space, ability to fuse 2 images
what is the consequence of BV being disrupted in its development stages?
Anything that interrupts, development of BV will stops at that stage.
Unlikely to get improvement in BV thereafter.
Earlier disruption will results in
worse and longer breakdown
what is spatial localisation?
Perception of direction of an object in space with respect to the eye
Visual space not always exactly the same as the real space/physical space.
Even so, the visual system invariably assumes its interpretation is correct
what is visual direction?
Visual direction = Visual line = line of sight
visual line passes specifically from the fovea to an object of regard (fixation point) = principal visual direction
Principal Visual Direction: on fovea
Secondary Visual Direction: on Nasal/Temporal retina
Local Sign: the capacity of visual neurons to process direction
what is retinal correspondence
Foveae have common visual direction
Nasal elements of one eye correspond with temporal elements of the other eye
what is the cyclopean eye?
Cyclopean eye = an imaginary point in the head that acts as centre of both eyes combined. serves as the origin for such directional judgments
what is panums fusional area?
narrow band around the horopter. an area in the retina of one eye, any point of which when stimulated simultaneously with a single point in the retina of the other eye will give rise to a single perception.
range of disparities allowing fusion and stereopsis
what is a horopter?
surface in physical space upon which objects lie which stimulate corresponding retinal points in each eye for a given fixation distance
seen and single, no dispparity and no stereopsis
what is physiological diplopia?
a type of diplopia which exists in the presence of binocular vision
consists of the appreciation that a near object appears double when a distant object is fixated (heteronymous or crossed diplopia)
and a distant object appears double when a near object is fixated (homonymous or uncrossed diplopia)
what causes physiological diplopia? what does physiological diplopia indicate?
All objects outside Panum’s Fusional Area (PFA) give rise to physiological diplopia.
Physiological diplopia indicates that the patient is capable of using both eyes together and is not suppressing one eye.
