Midterm Flashcards
Conscious and purposeful fixation at an object of regard
Voluntary
Involuntary fixation such as may occur in response to peripheral retinal stimulation
Reflex
A rapid change of fixation from one point in the visual field to another
Saccadic/Jump Fixation
Continued fixation of a moving object, implying a dynamic movement of the eye so as to keep the image of the object continuously on the fovea
Pursuit
Series of rapid fixations associated with an attempt to survey quickly the details of a view subtending a relatively large area of the visual field
Scanning
Continuous and fixed fixation of a non-moving object for a given period of time
Steady
An imaginary eye located between the two physical eye which serves to represent the two retinas
Cyclopean eye/ binnoculus
Retinal elements of the two eyes that share a common subjective visual direction are called
Corresponding retinal points
Both the foveas have a common visual direction and the retinal elements nasal to the fovea in one eye correspond to the retinal elements temporal to the fovea of the other eye.
Normal Retinal Correspondence
when the fovea of one eye has a common visual direction with an extrafoveal area in the other eye it is
ARC
A condition in which the two foveas have different visual direction
ARC
Process by which a single cortical image is perceived as a result of two separate ocular ones
Fusion
States that fusion operates upon a psychological and cerebral level
Worth’s theory
“Theory of Replacement”/ “Theory of Retinal Rivalry”
Verhoeff’s theory
Based upon alternate shifting mosaic patterns from each ocular image, in which portions of ocular image of one eye combines with portions from the other, in varying pattern to form the final unified or single perceptual image
Verhoeff’s theory
Maintains that single image is merely a projection of two identical images to the same perceptual position and that two ocular images are perceived as one because of their community location
Wall’s theory
Superimposition or simultaneous (first degree fusion) of two ocular images (e.g., a bird in the cage) requires stimulation of retinal areas having common visual directions.
GRADE 1: Superimposition/Simultaneous Perception
It is defined as sensory fusion in which the resultant percept is two-dimensional
GRADE 2: Flat Fusion
Highest form of fusion
Ability to judge distant objects
Stereopsis (third degree fusion) is the binocular visual perception of threedimensional space based on retinal disparity.
GRADE 3: Stereopsis/Depth Perception
It is the ability to distinguish disparity
Depth perception: stereopsis
It is the depth perception for distance and is also used to imply the visual perception of three dimensional spaces.
Depth perception: stereopsis
Requirements for Fusion
Equal or nearly equal visual acuity between two eyes
Monocular fixation of each eye
Normal sensorial relationship or normal retinal correspondence
Normal ocular motility
Representation of the crossed and uncrossed optic nerve fibers in the occipital cortex
movement of the eye that happens automatically as a reaction to something.
Reflex eye movement
Types of reflex eye movement
Vestibulo-ocular reflex
Optokinetic reflex
Pupillary reflex
Accommodative reflex
Corneal reflex
It produces eye movement in response to changes in head position
This is an extraordinarily accurate reflex that allows the eyes to remain focused on a target when the head moves
VOR
It is seen when an individual follows a moving object with their eyes, which then moves out of the field of vision at which point their eye moves back to the position it was in when it first saw the object
Optokinetic reflex
is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the pupil and the eye, thereby assisting in adaptation to various levels of lightness/darkness.
PLR
is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence, lens shape and pupil size (accommodation)
AR
is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), or bright light, though could result from any peripheral stimulus.
Corneal reflex
Because of their small magnitude, eye movements during fixation are also referred to as
Micro or miniature eye movements
Categories of steady fixation
Ocular microtremor
Ocular drifts
Microsaccades
Tremor is present when the amplitude of fixation tremor is on the order of the diameter of the smallest cone.
Ocular micrometer