What is also known as Dark Focus?
What is the cause of night myopia under total or relative darkness?
What is the expected amount of tonic accommodation?
1/2 to 1.5 diopters
What is the cause of tonic accommodation?
the balance between the parasympatheric and sympathetic nervous system
What type of accommodation is used to obtain clear focus and is linked to changes in stimulus distance?
What is also known as Psychic accommodation or instrument myopia?
What is a normal AC/a ratio?
What is a normal CA/c ratio?
0.06 D/ change in PD
What is the average latency of accommodation?
What is the response time for accommodation?
about 1 sec
What are three stimuli for accommodation?
In the accommodative stimulus -response curve, at what point is the hard saturation met?
amplitude of accommodation
What are the components of an accommodative lead?
tonic accommodation plus depth of focus
What are three factors that can affect the accommodative response?
True or False
The accommodative response is greatest when the stimulation is peripheral.
What factors determine the accommodative response?
depth of focus/pupil size
physical properties of the lens
Describe the neural pathway until the FEF?
Optic nerve-Optic tract-LGN-Optic radiations-Visual Cortex-Frontal eye Fields
Describe the efferent pathway of accommodation?
FEF-EW nucleus-CN III- ciliary ganglion- short ciliary nerve
What neural input is thought to relax accommodation?
What is the maximum motor output of the accommodative system known as?
amplitude of accommodation
What are the two methods to determine amplitude of accommodation?
Donders Push up
Minus Lens Blur
How is facility of accommodation measured?
True or False,
For most patients, the accommodative response is greater than the stimulus to accommodate.
False most have a lag not a lead
What is the expected lag of accommodation?
1/2 to 3/4 a diopter
What are four tests of posture of accommodation?
What effect do minus lenses have on accommodative vergence?
Minus lens induce accommodation, increase accommodative vergence and result in an eso deviation
What effect do plus lenses have on accommodative vergence?
Plus lens reduce accommodative vergence because they relax accommodation and therefore result in an exo deviation
What is a test that measures accommodation for computer users?
the PRIO System
What condition includes a high lag and can respond well to VT?
What condition of accommodation is characterized by a lead of accommodation and is harder to treat with VT?
The inability to shift accommodation rapidly is know as _____?
What are three common conditions that will present with errors in the accommodation system?
What do the high level cortical processes control in saccades?
calculation of eye position
modifies the final signal
What do lower level cortical control processes control in saccades?
the structures involved in the actual pulse step signal- the ocular motor neurons
What structures control when to generate a saccade?
cortex and the superior colliculus
What do the frontal eye fields and parietal lobe do during saccades?
They receive information about where to move the eyes and pass it to the superior colliculus
What is the primary function of the frontal eye field during saccades?
select the targets for future foveation
The frontal eye fields are associated with (voluntary/involuntary) saccades?
What is responsible for involuntary or reflex saccades?
The posterior parietal cortex, POT jxn
A lesion in the FEF or the POT junction will have what effect on saccades?
What acts to calibrate saccades?
What does the superior colliculus do in saccades?
processes information form the FEF, encodes the desired change and then sends it to the brainstem
Where do superior colliculus projections terminate?
The amplitude and direction of a saccade information is sent from what structure?
the parietal lobe
Lower level processing of in the saccade is the synchronization of what two elements?
Burst and pause neurons
Burst Neurons in the PPRF are responsible for what type of saccade?
Where do burst neurons reside?
PPRF and riMLF
Where are pause neurons located?
nucleus raphe interpositus
What is the role of the excitatory burst neuron?
they generate the pulse signal just before and during the saccade
What is the role of the inhibitory burst neuron?
they inhibit the antagonist muscles
The pulse signal is the peak________ of a saccade?
velocity and amplitude
When do pause neurons fire?
in the absence of saccades, ie during fixation
What is the key function of the pause neuron of the saccade?
they allow the saccade to occur, only after the pause neurons are inhibited can the burst neurons activate
What neurons produce the step signal?
Where are tonic neurons located?
in the nucleus prepositus hypoglossi (NPH)
What happens at the NPH during a saccade?
the burst signal is integrated to step signal
What are four classes of saccades?
What type of saccade is used attend to a remembered location, to command, or to perform an antisaccade?
When are quick phase saccades performed?
VOR and OKN
What are four reasons that saccades may have reduced velocity?
Meds side effects
Peripheral Nerve Palsy
Inaccurate saccades can likely be traced to what area for a pathology?
Why can one predict that parkinsons disease will affect saccades?
because the substania nigra is primarily affected and it projects to the superior colliculus
What saccadic test is used in dementia patients?
What patients will have marked difficulty in the antisaccade test?
frontal lobe lesions
What is the super imposition of unlike targets?
first degree fusion
What is second degree fusion?
Fusion of targets that have like contours
What is also known as flat fusion or fusion without depth?
What is the third degree of fusion?
What two things will the visual system use if two images can't be fused?
Anamalous retinal correspondence or suppression
If a strabismic patient suppresses what are the states of his motor and sensory fusion?
both are bad
If a strabismic patient uses anomalous correspondence to compensate what is the state of his motor and sensory fusion?
motor is bad but sensory is good
The theory that two monocular views will mutually inhibit each other is called what?
Alternation theory of fusion or the suppression theory
An example of the alternation in the alternation theory is_____
When does alternation occur?
when grossly dissimilar objects are presented to each eye
What is horror-fusionalis?
the inability to maintain sensory fusion
Images that are formed on corresponding retinal points are seen as________?
True or False
Only images that fall on corresponding points can be fused to a single image?
What is the region around the horopter that allows single vision?
Panum's Fusional Area
Panums fusional area size is measured in what?
minutes of arc
The magnitude of fixation disparity cannot exceed __________ if one is to maintain single vision?
True or False
Panums Fusional Area is larger vertically than horizontally?
False- 3-6X larger horizontally
What is the size of PFA at the fovea?
5 to 20 moa
What is the relationship between low temporal and spatial frequencies and PFA?
they both allow for a larger PFA
High temporal and spatial frequencies have what effect of PFA?
they both cause a reduction in PFA
What three things allow for a large panums fusional area?
peripheral retina stimulation
low spatial frequency
low temporal frequency
What is Utroclur discrimination?
the ability to determine which eye has been stimulated
True or False
Humans cannot make untrocular discriminations?
true- monocular information is lost
What is dichoptic stimulation?
presenting targets to each eye independently
What are two clinical applications dichoptic stimulation?
binocular refraction and testing suppression
What is responsible for the maintenance of binocular vision in the presence of a phoria?
When will fixation disparity be seen as single?
when it is inside panums fusional area
How many MOA equal one prism diopter?
A clinical measurement of a fixation disparity will have what two parts?
a binocular fusion lock and two nonius lines
What are some clinical tests to measure fixation disparity?
Bernell test Lantern
What is the distances used for the bernell test lantern?
distance and near
The borish card is used only at what distances?
near and intermediate
On a wesson card if the bottom line is seen to the right of the top line it is consistent with what type of deviation?
How long can the fast fusional system maintain control?
about one second
What activates the fast fusional system?
True or False
A patient that presents with prism adaptation does not have a healthy vergence system
false, PA is a sign of a good vergence system
Describe a fixation disparity curve type I?
Sine wave with a flatter central region and steeper peripheral, most patients
What is a type II fixation disparity curve?
doesn't cross into the exo portion, 20 to 25 percent of pts, most are esophoria, highly adaptive to base out prism
What is a type III fixation disparity curve?
doesn't cross into the eso portion, about 10 percent of patients, most likely exophoric
WHat is a type IV fixation disparity curve?
small flat sine wave, no phoria, possible anisokonia
What are the effects of vision therapy on the FD curve?
flattens the slope
Which patient will be more likely to be symptomatic on the FDC on with a flatter or steeper slope?
What is a good starting point for prism prescription from the FD curve?
1/2 the associated phoria
What is the point at which the FD curve crosses the Y axis?
What is the x intercept in the FD curve?
The ability of a visual neuron to process direction is referred to as?
Where are local signs referenced to?
What is the fovea's local sign?
principle visual direction
What is the neurological remapping where the PVD is no longer defined by the fovea, involuntarily?
What is the difference in eccentric viewing and eccentric fixation?
in viewing the fovea is still in control of PVD but in EF a new spot is reassigned to be the fovea
What is the egocenter or cyclopean eye theory?
that under binocular conditions we see directions relative to a single point within our head
Two points lying on the Vieth-Muller circle should be seen as_______?
single points without depth
Points nearer than the vieth-muller circle will result in what?
Points distant to the vieth-muller circle will result in what?
Objects that don;t stimulate corresponding points are said to be?
How much binocular disparity is perceived by corresponding retinal points?
Horizontal binocular disparity allows for the perception of what?
What is the spatial map of all corresponding retinal points?
Objects located on the horopter fall on _______ points?
What theory states that all corresponding points are evenly spaced with equal angles relative to the PVD?
What are the methods for measuring the horopter?
AFPP aka stereoscopic matching
What is more curved the horopter or the Vieth-Muller circle?
the Vieth-Muller circle
The distance between the Horopter and the VM circle?
At a point H>0 where is the horopter in relation to the V-M circle?
At a point where H<0 where is the horopter in relation to the V-M circle?
What are three things that can effect the shape of the horopter?
At greater fixation distances the horopter becomes_______?
At near fixation the horopter is_____?
What is the Abathic distance?
The point where the perceived horopter is equal to the actual horopter
If the right eye image is larger what direction is the horopter moved towards?
toward the left
What is the direction of the vertical horopter?
top tilted away from the viewer
What direction does the horopter move in the presence of BO prism?
bows away from the observer
What direction does the horopter move in the presence of BI prism?
Horopter bows towards the observer
What is Flom's notch?
it is the notch of the horopter in some constant ET
What vergence is the difference in the anatomical position of rest and the physiological position of rest?
What is also known as dark vergence?
What is the clinically estimated measure of tonic vergence?
What is also known as psychic vergence?
At what point does proximity begin to influence vergence?
How is disparity vergence removed from the system?
occlude or prism
How is accommodative vergence system removed to measure proximal vergence?
use of a pinhole
Under an open loop condition how much can proximal vergence alter convergence
up to 40 percent
What is the effect on the target perception with increasing base out prism?
appears to be smaller and closer
If the target is percieved to be outside the intended target it appears?
What does SILO stand for?
Small in Large out
What is the most important type of vergence?
Fusional or disparity vergence
If two stimuli were suddenly moved forward together what is the effect on retinal disparity and accommodation?
disparity will increase but accommodation remains constant
Targets placed along the midline will stimulate what type of vergence?
symmetric disparity vergence
What disparity occurs when lines of sight cross in front of the OOR and requires a divergent movement to obtain fusion?
What type of disparity occurs when lines of sight cross behind the OOR and requires a convergence eye movement for fusion?
As the difficulty of the reading material increases so does_________?
What are the three types of regressions?
Clusters are two or more regressions for no apparent reason and are sometimes seen in what condition?
The directional attack is calculated using what formula?
regressions/number of fixations
What is the span of recognition for the average college student?
4 letters to the left of fixation and 7 to the left
True or false
Factors such as line length, topography, color and illumination have dramatic influence on fixation duration.
What is the typical college students reading rate?
200-350 words per minute
What type of scotoma is worst for reading eye movements?
right paracentral scotoma
A central scotoma has what effect on reading?
cause problems with identification and semantic processing
True or false
Dyslexics can have their eye movement disorders corrected by VT
It is a reading disability that shows with a least 2 years behind in reading level with at least a normal IQ
Which type of dyslexia is characterized by inability to uses phoenetics, has inaccurate return sweeps and clusters.
Which direction of the OKN is greater?
Nasal is greater than temporal
If the OKN remains markedly asymmetric after 3-6 months what is a problem?
binocular vision and neural system isn't maturing
What are the directions of the slow and fast phase of horizontal nystagmus when a lesion is present?
slow phase towards the lesion and fast away
What is the COWS mnemonic?
It refers to caloric testing. Cold water yields an opposite nystagmus. Warm is same side
The COWS mnemonic refers to what phase of the nystagmus?
What two things is the OKN response judged on?
nystagmus and after nystagmus
What part of the brain is stimulated in look nystagmus?
What part of the brain is stimulated in stare nystagmus?
What type of nystagmus has a well defined slow and fast phase?
What type of nystagmus has no defined fast phase?
When is the fovea not used in tracking of a pursuit?
under scotopic conditions and in patients using eccentric spots
True or False the pursuit system has a significant refractory period?
What is the average pursuit gain?
Pursuits are highly accurate up to what target velocities?
30-40 deg per second
What is a saccadic intrusion?
when the pursuit gain is either to high or too low and a saccade is used correctively
What are the two stages of a pursuit?
open vs closed loop
What is the open loop stage in a pursuit?
it is during the first 100 msec when the pursuit cannot be modified
What is the stimulus for pursuits?
pursuits are driven by velocity changes
Which pursuits are more accurate vertical or horizontal?
horizontal is more accurate
What are four factors that can effect pursuit function?
Aging has the most effect on what stage of the pursuits?
closed loop gain
When the pursuits are recalibrated, what portion of the brain is used in motor plasticity?
What is the pathway of a pursuit?
V1-MT, MST (POT jxn)-FEF-Contralateral floccus and dorsal vermis of the cerebellum-vestibular nuclei-ocular motor nuclei
What is the structure that first creates the pursuit signal?
the POT junction
What plays a role in the attention of motion in a pursuit?
the PPC ( posterior parietal cortex)
What are the two contralateral structures involved in the smooth pursuit?
cerebellum and Vestibular nuclei and NPH
What are the four classes of saccades?