Lecture 03 - Vision 2

Question 1

Visual Acuity Testing

Answer 1

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)

Question 2

Visual Fields Testing Principles

Answer 2

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

Question 3

Confrontational methods

Answer 3

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

Question 4

Machine methods

Answer 4

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

Question 5

Hill of vision

Answer 5

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

Question 6

Pupillary light reflex afferent pathway

Answer 6

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

Question 7

Pupillary light pathway processing center

Answer 7

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

Question 8

Pupillary light reflex efferent pathway

Answer 8

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

Question 9

Afferent pupillary defect

Answer 9

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

Question 10

Efferent pupillary defect

Answer 10

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

Question 11

Retinal Detachment

Answer 11

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

Question 12

Vitreous detachment

Answer 12

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

Question 13

Cortical Stroke

Answer 13

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

Question 14

Optic Nerve Compression

Answer 14

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