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
Compared to tremor, it is larger and slower.
Amplitudes are 2 to 5 minutes.
Direction of drifts is apparently uncorrelated between two eyes
Ocular drift
Are kind of fixational eye movement. They are small, jerk-like involuntary eye movements, similar to miniature versions of voluntary saccades.
They typically occur during prolonged visual fixation
Range an amplitude from 1 to 23 seconds
Microsaccades
Saccades subtypes
Volitional
Reflexive
Express saccades
Spontaneous
Quick phase of nystagmus
Exaggerated convergence is called
Cross eyed viewing
changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation, sometimes known as the
accommodation-convergence reflex.
Classification of Vergence According to Maddox:
1.) Tonic Vergence
2.) Accommodative Vergence
3.) Fusional Vergence
4.) Proximal Vergence
Vergence due to normal extraocular muscle tone, with no accommodation and no stimulus to binocular fusion.
Tonic vergence
blur-driven vergence
is that portion of the range of inward rotation of both eyes that occurs in response to an increase in optical power for focusing by the crystalline lens.
Minus lens stimulate accommodation and caused a vergence response in covered eye.
Accommodative vergence
Also known as:
disparity vergence
disparity-driven vergence
reflex vergence
Fusional vergence
vergence due to the awareness of a fixation object being near or far in the absence of disparity and of cues for accommodation. This includes also vergence that is due to a subject’s intent to fixate an object in the dark.
Proximal vergence
sometimes also called voluntary vergence
Fusional vergence
is measured by bringing an object to the nose and observing when the patient sees double, or one eye deviates out.
NPC
The simultaneous occurring cyclorotation (torsional movement) of both eyes which is performed in opposite directions to obtain or maintain single binocular vision.
Cyclovergence
A condition in which the eyes do not point in the same direction.
Strabismus
A sensorimotor anomaly of binocular integration resulting in the failure to maintain bifoveal alignment manifesting in a divergent (exotropia), convergent (esotropia), or vertical deviation of nonfixating eye.
Strabismus
a condition of involuntary eye movement, acquired in infancy or later in life, that may result in reduced or limited vision. Due to the involuntary movement of the eye, it is often called “dancing eyes”
Nystagmus
the eye movement elicited by the tracking of a moving field.
Optokinetic nystagmus
caused by dysfunction of the vestibular part of the inner ear, the nerve, the vestibular nucleus within the brainstem, or parts of the cerebellum that transmit signals to the vestibular nucleus
Vestibular Nystagmus
Is defined as nystagmus with the fast phase beating in a downward direction
Downbeat
defined as nystagmus with the fast phase beating in an upward direction.
Upbeat nystagmus
Nystagmus resulting from malfunction in the saccade and pursuit gaze systems is much less common than that due to fixation malfunction
is a rhythmic rotation of the eyes in which the 12 o’clock meridian of the limbus rotates, causing either intortion or extortion
Torsional nystagmus
Vergence dysfunctions
Convergence Insufficiency
Convergence Excess
Divergence Insufficiency
Divergence
Basic Eso
Basic
Mixed
Causes: Lesions of the vestibulocerebellum and underlying
medulla (eg, Arnold-Chiari malformation, microvascular disease with vertebrobasilar insufficiency, multiple sclerosis, Wernicke encephalopathy, encephalitis, lithium intoxication), Heat stroke
Downbeat
Causes: Medullary lesions, including perihypoglossal nuclei, the
adjacent medial vestibular nucleus, and the nucleus intercalatus (structures important in gaze holding), Lesions of the anterior vermis of the cerebellum, Benign paroxysmal positional vertigo
Upbeat
Causes: Lateral medullary syndrome (Wallenberg syndrome)
Torsional nystagmus
is a multivectorial nystagmus (ie, horizontal, vertical, circular, elliptical) with an equal velocity in each direction that may reflect brainstem or cerebellar dysfunction.
Congenital or acquired
Causes: Demyelinating disease, Monocular or binocular visual deprivation, Oculopalatal myoclonus, Internuclear ophthalmoplegia, Brainstem or cerebellar dysfunction
Pendular nystagmus
a well-recognized finding in patients with a unilateral disease of the cerebral hemispheres, especially with large, posterior lesions.
Horizontal nystagmus
consists of elevation and intorsion of one eye and depression and extorsion of the fellow eye that alternates every half cycle.
Seesaw nystagmus
eyes cannot be maintained at an eccentric orbital position and are pulled back toward primary position by the elastic forces of the orbital fascia.
Congenital nystagmus
Causes: Sedatives, tranquilizers, ethanol, and “Recreational drugs” can all cause nystagmus, Central (cerebellar or brainstem) lesion.
Gaze-evoked nystagmus
The presumed mechanism is disruption of the vestibulo-ocular tracts at the pontomedullary junction.
Periodic alternating nystagmus
nystagmus in the abducting eye
abnormalities of the abducting eye in internuclear ophthalmoplegia reflect an adaptive process (Hering’s law of equal innervation) that helps overcome the adduction weakness of the opposite eye.
Abducting Nystagmus of internuclear ophthalmoplegia
Subjective direction w/ the fovea when a given object is fixated
Principal visual direction
locus of all object points that are imaged on corresponding retinal elements at a given fixation distance.
Horopter
A.k.a. Theoretical horopter curve
Vieth-muller curve
This means that the distribution of the elements that correspond to each other is not the same in the nasal and temporal parts of the two retinas.
Empirical horopter curve
The region in front and back of the horopter in which single vision is present is known
Panum’s area of single binocular vision
refers to the direction of an object in space relative to one self, rather than the eyes.
Egocentric visual direction
Superimposed retinal images will be seen as being in alignment in the visual field, but at a different distance from the eye
Oculocentric visual direction
In which the angle of anomaly is equal to the objective angle of deviation. This indicates that the ARC fully corresponds to the strabismus.
Harmonius ARC
In which the angle of anomaly is less than the objective angle of deviation
Unharmonius ARC
When the angle of anomaly is greater than the objective angle of deviation
Paradoxical ARC
Assessment of relationship between the fovea of the fixing eye and the retinal area stimulated in the squinting eye.
Bagolinis striated glasses test
Worth 4 dot test
Red filter test
Synaptophore
Assessment of the visual directions of the two foveas. Included in this are:
After image test
Ophthalmoscopy
the hallmark of retinal correspondence
Single vision
the hallmark of retinal disparity
Diplopia
defined as the way that your left eye and your right eye view slightly different images.
Retinal disparity
is the basic instrument used for measuring or training binocular vision, for stimulating vision in an amblyopic eye and for increasing fusion of the eyes.
Major amblyoscope
Diagnostic uses of major amblyoscope
- Measurement of the objective and subjective angle of deviation.
- Measurement of angle kappa.
- Measurement of primary and secondary deviation.
- Measurement of deviation in cardinal directions of gaze.
- Estimation of status of binocular vision.
Therapeutic uses
- Suppression.
- ARC.
- Eccentric fixation (only in models that have special attachments with Haidinger Brushes).
- Accommodative esotropia (dissociation training).
- Heterophorias and intermittent heterotropias (improvement of fusional amplitudes)
