Intro To BV Flashcards
What is binocular vision
- eye receives a separate retinal image which is interpreted by the brain as a single common perception
- image is perceived as one
Advantages of binocular vision
- depth perception
- without BSV are reliant on monocular cues
- enhanced visual motor skills
- binocular summation
- VA, contrast sensitivity, motion
What is the perception of space
- visual system tells us what and where an image is seen
- where the image falls on the retina tells us location
What is visual direction
- projection is the term for object location in space, and depends on the part of the retina being stimulated
- each part of the retina has a given projection for a given distance of fixation
- termed visual sign or visual direction
- reference point for projection is the fovea as it has the principal visual direction
- all other points have secondary visual direction
What is the occulocentric visual direction
- visual direction can be represented by a line that joins the object and the fovea is principal direction
- all other points are occulocentric
What is egocentric visual direction
- egocentric visual direction refers to the direction of an object in space relative to one’s self, rather than the eyes
- determined by retinal direction
What is peripheral retinal correspondence
- same visual projection in both eyes
- right visual field stimulates point on temporal left retina, it falls on nasal in right
- same point in space, so retinal correspondence
What is cyclopean projection
- object fixed by 2 fovea appears to be located centrally on a cyclopean eye
- binocular projection can be considered from this
Which mechanisms does binocular single vision depend on
- development of binocular single vision depends on the coordination of the sensory aspects and the motor responses of the visual processes
What does the sensory mechanism include
- light sense
- form sense
- good VA
- colour sense
- spatial relationship, projection and localisation
What does sensory mechanism development require
clear refractive media
• Normal retina
• Cones
• Rods
• good VA
• Normal retinal correspondence
• Normal visual pathway from retina to cortex
• Normal proprioceptive receptors
• Reinforcement of stimulus
• Vestibular apparatus otilith and endolymph
• Nerve endings in neck muscles
What is the motor mechanism
- puts object of attention onto each fovea
- maintain fixation
- allow change of fixation
- ensure proper alignment
What does motor mechanism development rely on
• reinforcement of stimulus
• normal extra-ocular muscles & adnexae
• normal oculo-motor nerve nuclei and pathways inter-nuclear and supra-nuclear pathways
• lower motor neuron pathways controlling vestibular mechanisms
What links sensory and motor function
Postural and psycho-optical reflexes
What are postural reflexes
- inanate and controlled by visual stimuli
- to maintain posture despite changes in head position
- maintain orientation of eyes
Types of postural reflexes
- static postural reflex
- stato-kinetic postural reflex
What is a static postural reflex
- tonic labyrinthine - Stimulation of otolith muscles when head falls forward to move eyes up
- tonic neck - stimulation of proprioceptive nerve endings in the neck muscles when head is inclined
What is the stato-kinetic postural reflex
- stimulation of endolymph in semi-circular canals when head and body are rotated, results in physiological vestibular nystagmus
- these reflexes are present at birth but as visual function develops the control of posture becomes more dependant on the eyes
2 types of fusion
- sensory
- motor
What is sensory fusion
- ability to perceive 2 similar images
- images must fall on corresponding retinal areas
- similar in size, brightness and sharpness
What is retinal rivalry
- When dissimilar images re presented to corresponding retinal areas fusion is impossible
- these images cause conflict and one is temporarily suppressed
What is panums fusional space
- narrow band around the horopter within which object points give rise to binocular single vision
- elliptical in shape
