Lecture 03 - Vision 2 Flashcards Preview

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Flashcards in Lecture 03 - Vision 2 Deck (14):

Visual Acuity Testing

Acuity - ability to distinguish object from background
20 foot lane = standard
objects of diminishing size, monocular
smallest line read = acuity
function of central photoreceptors (cones)
20/25 = person needs 20 ft, while normal = 25
acuity = combo of # cells, types of cells, # neuronal connections (density of rods and cones from macula center)


Visual Fields Testing Principles

testing function of peripheral retina
test objects are large
necessary to document location of test image (create map of function - retinotopy)


Confrontational methods

-coarse test of function
-documented from patient's perspective as s/he would draw it on paper
***not how you see it


Machine methods

easier to standardize
-target size, distance, brightness and bacgkround
-hill of vission 0 central retina more sensitive than peripheral retina
-objects not seen peripherally will be seen centrally


Hill of vision

document hill surface
-seeing/non-seeing itnerface --> test with light
-boundary = seen 50% of time
target crosses the boundary
-figuratively (brightness)
-literally (motion)

-contour map
- each concentric line - boundary of seeing different brightness and/or diameter of test light


Pupillary light reflex afferent pathway

Retina --> ganglion cells --> Optic Nerve --> Chiasm --> tract --> BYPASSES LGN --> pretectal nucleus


Pupillary light pathway processing center

Pretectal inputs bilateral
--> Edinger-Wesphal (bilateral and symmetric)

-effect is summation/averaging (both pupils contract when light is shown on only one)
-monocular blindness = pupils still symmetric


Pupillary light reflex efferent pathway

Edinger-Westphal --> CN3 --> Ciliary Ganglion --> ciliary nerves via sclera --> Pupillary sphincter


Afferent pupillary defect

Afferent defect: neither pupil constricts
-OUTPUT is redued in one eye
-pretectum gets less signal, and reacts as though light is dimmer
-pupils dilate slightly
-swinging light back to intact eye, both pupils constrict slightly


Efferent pupillary defect

Efferent defect: only opposite constricts (left eye motor impairment/signal to cord.cortex ok but MN not)
-Efferent arm injured: pupil cannot constrict well
-sphincter rupture/CN3 lesion
-Pupils likely are NOT symmetric in any condition


Retinal Detachment

-flashes (lightning), floaters (opaque, large), "shade"
-blood in vitreous (floaters)
-detached retina floating freely in vitreous cavity --> undulating with eye movement (like seaweeds)

-Thin retina - hole forms - vitreous fluid flows between retina and retinal pigment epithelium
-retina falls away from REP, away from choroidal blood supply and rod/cone layer becomes ischemic

-acuity normal unless central retina detaches
-visual field completely loss in area of detachment
-pupillary light reflex normal if


Vitreous detachment

vitreous loses hydration throughout life and contracts, pulling away from retina --> no adhesion = no damage

-if vitreous attached to retina, can pull a hole in retina


Cortical Stroke

incidence increases with age and CV disease
-symptoms most likely if stroke affects other systems (esp cranial nerve/ motor control)
-may notice loss of vision "to the side"
-blood flow interrupted --> blockage of blood flow = ischemia
-rupture of vessel = hemorrhage
-loss of blood flow = rapid loss of cortical nerve function
-edema from ischemia = further compromise adjacent areas

-Acuity usually normal
-Visual field loss corresponding to area affected by stroke, respects vertical midline
-pupillary light reflex is normal


Optic Nerve Compression

extremely rare
-nerve sheath meningioma, pituitary tumor, ant. comm. artery aneurysm
-bitemporal hemianopsea
-pallor of optic nerve
-not cupping (glaucoma)
-bilateral if compressed at chiasm
-compression of nerve fibers = gradual atrophy and death of fibers

-acuity has little loss of central vision early, but late = blindeness
-visual field shows constriction of field (bilateral hemianopia if chiasm is affected --> tempral field affected)
-pupillary light reflex affected if nerve sheath affected --> asymmetric damage, but not if at chiasm --> loss is equal