Term
| 3 components of the visual pathway |
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Definition
visual pathway = cornea --> posterior cerebral hemispheres
optical
retinocortical
perceptual |
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Term
| clinical manifestations of OPTICAL disorders |
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Definition
diffusely blurred vision
unfocused image forms on the retina
-uncorrected refractive error
-damage to cornea, lens, or vitreous |
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Term
| clinical manifestations of RETINOCORTICAL disorders |
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Definition
blurry vision or discrete (focal) regions on reduced/absent vision ("scotomas")
-mapping of scotomas by visual field testing is very important for localization of the lesion |
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Term
| clinical manifestations of PERCEPTUAL disorders |
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Definition
normal optical and retinocortical function - UNABLE to perform complex cognitive functions related to vision: recognizing color, faces, objects, judging distance/motion
-occipito-temporal pathway: difficulty recognizing objects and color
-occipito-parietal pathway: difficulty distribution attention across multiple elements in a visual scene and appreciating spatial relationships and motion |
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Term
| tests for detecting optical defects |
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Definition
visual acuity testing
refraction
pinhole
slit lamp biomicroscopy
ophthalmoscopy |
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Term
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Definition
starting point of all ophthalmic exams
assess ability to discriminate fine achromatic detail (governed by fovea) |
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Term
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Definition
place screen with multiple 2.5 mm holes in front of eye
visual acuity will IMPROVE if there is a refractive error, media irregularity, or opacity (corneal scar or cataract) |
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Term
| tests for localization of retinocortical defects |
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Definition
ophthalmoscopy
pupillary reactions
visual field examination |
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Term
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Definition
lack of constriction to light = pre-geniculate lesion, or purely efferent disturbance
swinging light test checks for relative afferent pupil defect |
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Term
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Definition
afferent pupil defect (APD) in pupil that dilates
APD is virtually diagnostic of an ipsilateral optic nerve lesion (although severe retina lesions can also cause it) |
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Term
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Definition
| complements visual acuity testing assesses NON-foveal vision finger confrontation or bowl perimetry |
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Term
| finger confrontation visual field exam |
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Definition
good for detecting large and dense visual field defects
young children, illiterate, mentally impaired, uncooperative patients |
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Term
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Definition
patient indicates when they see the light stimulus (static and kinetic stimuli versions exist)
print-out of defects represents shape of the visual field defects and can be used to localize a lesion in the pathway based on the pattern
-retinalganglion
-optic chiasm
-optic tracts, optic radiations, visual cortex |
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Term
| *nerve fiber bundle defects* |
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Definition
visual field defects of retinal ganglion and optic nerve lesions
many take several shapes, "scotomas" |
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Term
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Definition
anatomy of the retinal nerve fiber layer
1: pathway carrying the foveal fibers needed for high grad acuity and color discrimination
2: pathway of arcuate fibers, in two compartments, that arch over the foveal fibers and enter optic disk from N and S poles
3: pathway of nasal fibers entering side of optic diskin a radial fashin |
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Term
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Definition
cecocentral scotoma
loose axons from the intervening area between the fovea and the blind spot
caused by lesions affecting axons originating in the macular region and the region between the macula and optic disk
-hereditary degenerations
-toxins
-nutritional deficiencies |
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Term
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Definition
central scotoma
caused by lesions affecting the axons originating in the macular (foveal) region
-optic neuritis
-hereditary degenerations
-toxins |
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Term
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Definition
arcuate scotoma
caused by lesions affecting axons coming from temporal retina that arch above or belong the macular axons; have a border ("step") along the horizontal meridian in the nasal field
-optic nerve infarction
-glaucoma
see more in disorders that affect myelin more than axons |
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Term
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Definition
temporal wedge scotoma
caused by damage to nasal radial axon bundles
-congenital anomalies
-inflammation |
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Term
| visual field defects of optic chiasm lesions |
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Definition
fibers originating in the nasal retina cross to the contralateral optic tract -- this is where most lesions of the optic chiasm occur
lesions of crossing fibers cause vision defects confined to temporal vision field
defect border always abuts on the visual field vertical meridian but does NOT CROSS into the nasal field (unless chiasm is completely destroyed) |
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Term
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Definition
visual field defect whose borders abut on the VERTICAL meridian
the entire visual hemifield need not be obliterated |
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Term
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Definition
bitemporal hemianopia - visual field defect of optic chiasm lesion
most comon pattern created by chiasmal-area lesions; lesion to crossing nasal fibers, can't see temporal visual field
-pituitary tumor
-craniopharyngioma
-astrocytoma
-sphenoid meningioma
-carotid artery aneurysm
these tumor lesions often treatable! |
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Term
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Definition
VISUAL CORTEX
^
optic radiations
^
lateral geniculate nucleus (LGN)
^
optic tract |
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Term
| visual field defects of retrochiasmal lesions |
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Definition
the retro-chiasmal pathway carries fibers from temporal retina of one (ipsilateral to cortex) eye, and the nasal retinal of the other eye (contralateral to cortex)= visual information from only one visual space (contralateral to that cortex)
lesions anywhere in path produce visual defect of entire hemi-visual world on side contralateral to lesion |
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Term
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Definition
homonymous hemianopia from retrochiasmal lesion (anywhere behind optic chiasm in the visual pathway)
L-sided lesion, loss of vision:
L nasal field
R temporal field |
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Term
| evaluating perceptual disorders |
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Definition
WHAT? - faces/places
lesions of occipito-TEMPORAL pathway - trouble recognizing colors, familiar faces, objects, places
WHERE? - spaces
lesions of occipito-PARIETAL pathway - misreaches for objects, has poor motion detection, trouble reading, constructing puzzles, interpreting pictures |
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Term
| tasks of the occulo-motor system |
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Definition
1. place the image of the object of regard onto the fovea of each retin
GAZE SHIFTING
2. keep the object there as the object or viewer moves
GAZE-HOLDING |
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Term
| subsystems of the ocular motor system to help accomplish gaze-shifting and gaze-holding |
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Definition
saccades
pursuit
vergence
vestibulo-ocular |
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Term
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Definition
predominantly volitional action to move the eyes from one quidistant target to another
visually or non-visually guided |
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Term
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Definition
REM
fast phases of nystagmus
random |
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Term
| control of horizontal saccades |
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Definition
2 main cerebral centers: frontal eye field, parieto-occipital
to PPRF (pontine paramedian reticular formation) via basal ganglia/superior colliculus
pons to CN VI nucleus (final common nucleus for control of horizontal gaze)
CN VI nuc to lateral rectus muscle and to contralateral medial rectus via MLF to contralateral CN III nucleus |
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Term
| control of vertical saccades |
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Definition
cerebrum (frontal eye field and parieto-occipital junction) to MIDBRAIN (rostral interstitial nucleus of the medial longitudinal fasciculus-riMLF)
anatomical dissociation from upwards and downwards gaze
up: riMLF through nucleus of Cahal and posterior commisure to superior rectus subnucleus (CN III); inferior oblique subnucleus(CN III)
down: riMLF to inferior rectus subnucleus (CN III) and superior oblique nucleus (CN IV) |
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Term
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Definition
pathway between CN VI and III nuclei
very important pathway
very vulnerable, especially in MS (white matter tract that gets hit) |
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Term
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Definition
internucleal ophthalmoplegia
can move eye lateral, but can't move contralateral eye medial
often seen in MS patients |
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Term
| problems with horizontal vs. vertical gaze |
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Definition
if horizontal, indicates pontine lesion
if vertical, indicates midbrain lesion |
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Term
| lesions of saccadic pathway |
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Definition
casue saccades that are:
too small (hypometric)
too slow
inaccurate (dysmetric)
delayed in onset
completely absent (gaze palsy)
intrusive |
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Term
large, acute cerebral hemisphere lesion
-saccadic effect |
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Definition
absent, small, or slow saccades in the direction CONTRALATERAL to the side of the lesion
eyes are often initially deviated toward the side of the lesion |
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Term
bilateral cerebral lesion
-saccadic effect |
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Definition
| impair saccades in all directions |
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Term
pontine lesion
-saccadic effect |
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Definition
deficits ipsilateral to the side of the lesion
impair both volitional and reflex gaze |
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Term
| supranuclear gaze distrubance |
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Definition
dissociation between impaired volitional and intact reflex eye movement
no voluntary saccade, but can get eyes to move horizontal with doll's eye reflex maneuver |
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Term
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Definition
maintains fixation of slowly moving targets
saccades catch up if this fails
most vulnerable of all subsystems to diffuse brain insult (metabolic, traumatic, toxic, fatigue, meds, aging) |
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Term
| features of pursuit system |
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Definition
hemispheric control is ipsilateral
PPRF and riMLF centers are NOT involved |
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Term
| control of horizontal pursuit |
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Definition
generated in occipito-parietal region; must be able to see in order to pursue
parieto-occipital junction (POJ) and some visual cortex input to temporo-occipital junciton that then gets sent down the brainstem to ipsilateral dorsolateral pontine nucleus (DLPN)
distributed to cerebellar vermis, nucleus prepositus hypoglossi, medial vestibular and then to CN VI nucleus for horizontal pursuit (and to midbrain to vertical pursuit) |
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Term
| lesions of pursuit pathway |
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Definition
cause "cogwheel" or "saccadic" eye movements
pursuit is affected in all directions with neuro disease that effect the brain diffusely or symmetrically |
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Term
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Definition
move eyes closer together = convergence
-looking from far to near
move eyes farther apart = divergence |
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Term
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Definition
(less understood)
eye movement command prob originates in occipito-parietal area bilaterally
conveyed to a midbrain centers
on to CN III and IV |
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Term
| lesions affecting vergence subsystem |
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Definition
usually located in the diencephalon or midbrain
excessive of insufficient vergence, excessive accommodation |
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Term
| vestibulo-ocular subsystem |
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Definition
| presents image slip during head movements |
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Term
| control of vestibulo-ocular reflex |
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Definition
generated in labyrinths; pathway does not reach cerebrum (goes directly to output centers)
signal from semi circular canals goes to medial vestibular nuclei and to CN VI for horizontal eye movements, to CN III & IV for vertical eye movements |
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Term
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Definition
assess VOR in unconscious patient and in alert patients who have very reduced volitional excursions of eyes
if positive (eyes stay fixed with head turn), lesion gasuing gaze disturbance must lie rostral to the brainstem gaze centers |
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Term
| vestibulo-ocular disorders |
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Definition
bilateral symmetric hyofunction --> "oscillopsia"
sense that the image is jiggling
lesion of only ONE VOR pathway creates nystagmus |
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