Visual System Flashcards
how are lesions of the visual system described?
- in terms of their visual field deficits
- visual field deficits are described from the perspective o the pt’s right or left
what are the four quadrants of the retina and what visual quadrants do they receive?
- upper nasal visual quadrant–projects to lower temporal retinal quadrant
- lower nasal visual quadrant–projects to upper temporal retinal quadrant
- upper temporal visual quadrant–projects to lower nasal retinal quadrant
- lower temporal visual quadrant–projects to upper nasal retinal quadreant
where do axons of the ganglion cells terminate?
- majority terminate in the lateral geniculate body
- rest terminate in the superior colliculus as part of the tectal and visual reflex pathways
rules of retinotopic projection
- fibers from the temporal hemiretina do not cross in the optic chasm
- fibers from the nasal hemiretina cross in the optic chimes
Rule of L’s
- info from the lower hemiretina projects to:
- lateral part of the lateral geniculate body
- loop of meyer
- lingual gyrus
homonymous visual fields
- refer to corresponding halves of visual fields such as the temporal field of one eye and the nasal field of other
- Left temporal and R Nasal
- R temporal and L Nasal
heteronymous visual fields
- refer to non corresponding visual fields
- temporal field in the L and temporal field in the R
- nasal field in the L and temporal field in the R
hemianopsia
- blindness in one half of the visual field
* *nasal hemianopsia of the L eye indicates a lesion of the temporal hemiretina of the L eye
quadrantanopia
- blindness of a quadrant of the visual field
- most common involves the upper nasal quadrant of one eye and the upper temporal quadrant of the other eye called superior quadrantanopia–homonymous condition
binasal hemianopsia
- cause: bilateral lesion of the lateral aspect of the optic chiasm
- results: heteronymous blindness in the nasal fields of each eye
- may also be unilateral due to atherosclerosis of ICA
- ex: if bilateral lesion of the lateral aspect of optic chasm, blindness in the R and L nasal visual fields
unilateral nasal hemianopsia
- cause: unilateral lesion of the lateral aspect of the optic chiasm
- results: nasal hemianopsia (blindness) of the ipsilateral eye
- ex: lesion of the lateral aspect of the L optic chiasm results in (right) nasal hemianopsia of the left eye
- blindness in the nasal field of the left eye
bitemporal hemianopsia
- cause: midline lesion of the medial portion of the optic chiasm
- one type is due to a pituitary tumor
- results: bitemporal hemianopsia (blindness)
- ex: so if lesion to the medial aspect of the optic chasm, then blindness occurs in the temporal fields of both eyes
contralateral homonymous hemianopsia
- cause: unilateral lesion of the lateral geniculate body, complete optic radiations, or visual cortex
- results: contralateral homonymous hemianopsia
- ex: left homonymous hemianopsia due to a lesion on the R visual pathway (ie. optic tract, lateral geniculate body, optic radiations)
contralateral superior quadrantanopia
- cause: unilateral lesions of the loop of Meyer
- possibly due to a tumor of infarction of the posterior temporal lobe
- results: homonymous deficit
- ex: left superior quadrantanopia–due to a lesion in the R loop of Meyer causing blindness in the L temporal visual field and R nasal visual field
incongruent contralateral homonymous hemianopsia with macular sparing
- cause: unilateral lesion of the visual cortex
- possibly due to obstruction of the posterior cerebral artery
- results: contralateral hemianopsia that is not symmetrical in both eyes and does not occur in the macula
- lesions of the visual cortex are incongruous while lesions of the LGB or optic radiations are congruous
- ex: left incongruent homonymous hemianopsia with macular sparing–due to a lesion with the R primary visual cortex
- causes blindness in the L half of each eye (L temporal field and R nasal field) leaving the macula spared–not symmetrical on each side
visual agnosia
- pts are unable to visually recognize objects or pictures
- may be due to bilateral damage in the visual assoc cortices secondary to anoxia
associative visual agnosia
- infarction of the L occipital lobe and posterior corpus callous secondary to occlusion of the PCA
- disconnects the language area from the visual assoc cortex
- pt cannot name or describe an object in the visual field, but they can recognize and demonstrate their use
- visual perception intact
- pts are usually alexic (unable to read) and writing ability may be affected (agraphia)
prosopagnosia
- once a visual field is processed in the primary and associative visual cortices, it may be correlated with memory
- bilateral lesions in the occipito-temporal regions may result in bizarre disturbance of fine visual discrimination and ability to recognize extremely familiar faces
light reflex
-pupillary compression assoc with a normal response to shining an exam light into the pt’s eye is a PS mediated response that is processed thru the PRETECTUM
-shining a light in an eye results in ipsilateral constriction of the pupil–>direct light reflex
light into R eye–>R retina–>optic N–>optic tract–>brachium of superior colliculus–>superior colliculus–>pretectum–>Edinger Westphal Nucleus–>Oculomotor N–>Ciliary Ganglion–>pupillary constrictor M–>ipsilateral pupillary constriction
-unilateral stimulus will also normally elicit pupillary constriction of the contralateral eye–consensual pupillary reflex
light into R eye->R retina–>optic N–>optic tract–>brachium of superior colliculus–>superior colliculus–>pretectum–>posterior commissure–>Edinger Westphal Nucleus–>Oculomotor N–>Ciliary Ganglion–>pupillary constrictor M–>ipsilateral pupillary constriction
pupillary dilation response
- dec in the amount of light reaching retina results in bilateral reflex dilation of the pupils
- sympathetic response mediated by brainstem and upper SC
dec light–>retina–>optic N–>superior colliculus–>pretectum–>reticular formation–>lateral reticulospinal tract–>preganglionic sympathetic neurons–>superior cervical ganglion–>pupillary dilator Ms–>pupillary dilation
accomodation
- cortically mediated visual response
- originates in frontal eye field of frontal lobe
- triad of accommodation: convergence of vision, pupillary constriction, thickening of lens
Argyll Robertson pupil
- result of syphilis infection
- pupils are unreactive to light but constrict during accommodation
- due to destruction of pretectum–important in light reflex but not accommodation
- accomodating but unreactive–Prostitute’s Pupil
Holmes Adie Pupil
- benign condition
- may be due to lesion of ciliary ganglion
- may confused with Argyll Robertson b/c of similar rxn to light, but distinguished by different rxns to accomodation
voluntary movements of the eye
- controlled by frontal eye fields in the posterior portion of the middle frontal gyrus
- corticotectal fibers descend to superior colliculus which in turn influences the motor neurons of III, IV, and VI
convolutional movements of eye
- controlled by occipital eye fields in the visual assoc cortex
- fibers from the occipital cortex descend as corticotectal fibers to superior colliculus which influence the LMNs of III, IV, VI
