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?
In the accommodative stimulus -response curve, at what point is the hard saturation met?
amplitude of accommodation
What are three factors that can affect the accommodative response?
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
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 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 condition of accommodation is characterized by a lead of accommodation and is harder to treat with VT?
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 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
A lesion in the FEF or the POT junction will have what effect on 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
Lower level processing of in the saccade is the synchronization of what two elements?
Burst and pause neurons
What is the role of the excitatory burst neuron?
they generate the pulse signal just before and during the saccade
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 type of saccade is used attend to a remembered location, to command, or to perform an antisaccade?
What are four reasons that saccades may have reduced velocity?
Meds side effects
Peripheral Nerve Palsy
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 patients will have marked difficulty in the antisaccade test?
frontal lobe lesions
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
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 relationship between low temporal and spatial frequencies and PFA?
they both allow for a larger PFA
What three things allow for a large panums fusional area?
peripheral retina stimulation
low spatial frequency
low temporal frequency
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?
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
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?
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
Which patient will be more likely to be symptomatic on the FDC on with a flatter or steeper slope?
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
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 are three things that can effect the shape of the horopter?
What is the Abathic distance?
The point where the perceived horopter is equal to the actual horopter
What direction does the horopter move in the presence of BI prism?
Horopter bows towards the observer
What vergence is the difference in the anatomical position of rest and the physiological position of rest?
What is the effect on the target perception with increasing base out prism?
appears to be smaller and closer
If two stimuli were suddenly moved forward together what is the effect on retinal disparity and accommodation?
disparity will increase but accommodation remains constant
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?
Clusters are two or more regressions for no apparent reason and are sometimes seen in what condition?
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.
A central scotoma has what effect on reading?
cause problems with identification and semantic processing
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.
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
When is the fovea not used in tracking of a pursuit?
under scotopic conditions and in patients using eccentric spots
What is a saccadic intrusion?
when the pursuit gain is either to high or too low and a saccade is used correctively
What is the open loop stage in a pursuit?
it is during the first 100 msec when the pursuit cannot be modified
What are four factors that can effect pursuit function?
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 are the two contralateral structures involved in the smooth pursuit?
cerebellum and Vestibular nuclei and NPH