VERGENCE AND ACCOMMODATION Flashcards
What is binocular vision (BV)?
Vision with two eyes working as a functional pair to produce a single image of a stimulus in space.
What are the sensory components of BV?
Integrating information from both eyes into a single percept
Using two eyes as a sensory unit a function of the brain
What are the motor components of BV?
Eye muscle co-ordination is required to ensure both eyes are aiming in the same direction
What does functional binocular vision require?
- Overlapping visual fields
- R&L eyes to give slightly different perspectives of the same scene
- This enables potential for stereopsis
What happens when converging for a near stimuli?
When converging for near stimuli, the two eyes point in different directions
What is retinal disparity?
An angular subtense of deviation of an image from corresponding points
- a slight difference in the two retinal images due to the angle from which each eye views an object
What is vergence?
A reflex, unconscious process driven by multiple factors & fine-tuned by retinal disparity
- vergence eye movements align both visual axes on objects of interest at varying distances
What is accommodation?
A large reflex, unconscious process driven primarily by retinal defocus
- a process where ciliary muscles function to change the focal length of the eyes so that the image is formed in the retina
What is the near triad?
Involves accommodation, convergence and pupil constriction
What AC/A ratio?
This measures the changes in vergence posture (eso or exo) for unit change in accommodation
e.g. 4:1 ratio means vergence alters by 4 prims for every dioptre of accommodation change that is induced.
It is a direct measure of accommodative vergence
What is the gradient method of measuring AC/A ratio?
Phoria is measured with added lenses & test distance stable
Dissociated phoria with no lenses, +/-1 & +/-2
Must control accommodation
Evaluate ratio separately for minus and plus lenses
What is angle kappa?
The angle between the visual axis (line connecting the fixation point with the fovea) and the pupillary axis (line that perpendicularly passes through the entrance pupil and the centre of curvature of the cornea).
