Lecture 03 - Vision 2 Flashcards Preview

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Flashcards in Lecture 03 - Vision 2 Deck (14):
1

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)

2

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)

3

Confrontational methods

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

4

Machine methods

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

5

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

6

Pupillary light reflex afferent pathway

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

7

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

8

Pupillary light reflex efferent pathway

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

9

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

10

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

11

Retinal Detachment

1/1000/year
-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

12

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

13

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

14

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