Visual System Lesions

Question 1

Pupillary light reflex

Answer 1

. Afferent: retinal relays from photoreceptors to bipolar cells to ganglion cells that enter brachium of sup. Colliculus to pretectal area
. Assoc. limb: pretectal nucleus sends axons to edinger-Westphal nuclei, projection to contralat. E-W nucleus decussate in post. Commissural
. Efferent limb: cells in E-W nuclei send axons cia CN III to postganglionic neuron in ciliary ganglia that cause PNS stim and pupil constriction

Question 2

Lesion in afferent limb of pupillary reflex

Answer 2

. Light shown into affected eye shows no response in either eye
. Light shown in healthy eye shows constriction in both eyes

Question 3

Lesion in efferent limb of pupillary reflex

Answer 3

. Affected eye shows no direct or consensual light reflex
. Healthy eye shows both response
. Pupil of affected eye is larger than healthy pupil due to unopposed pupillary dilator mm.

Question 4

Near (accommodation-convergence) reflex

Answer 4

. Brain sees an out-of-focus object and reflexively brings it into focus
. Reflex tests change in focus from a far object to a near object resulting in ocular convergence, lens thickening, and pupillary constriction

Question 5

Argyll-Robertson pupil

Answer 5

. Small, irregular, and fixed to light
. Constricts in response to accommodation
. Lesion in pretectum is presumed cause due to neurosyphilis or other tumors

Question 6

Scotoma

Answer 6

. Small visual field deficit

Question 7

Anopsia (anopia)

Answer 7

. Large visual field deficient
. Hemianopsia: 1/2 visual field lost
. Homonymous: visual field deficit is same for both eyes
. Heteronymous: visual field deficit occurs in opposite halves of the eyes
. Quadrantanopsia: deficit in 1/4 of visual field, designated and superior or inferior

Question 8

Optic n. Lesion

Answer 8

. Complete blindness in corresponding eye

. Caused by trauma or degenerative disease

Question 9

Optic chiasm lesion

Answer 9

. Bitemporal heteronymous hemianopsia
. Due to pituitary tumor impinging on decussating fibers from temporal visual fields of both eyes
. Tunnel vision
. Due to retinotopic organization of these fibers
. Early stages of tumor growth would affect inf. Fibers in decussation (sup. Temporal visual quadrants causing sup. Quadrantanopsia)

Question 10

Lateral optic chiasm lesion

Answer 10

. Ipsilat. Hemianopsia
. Due to aneurysm of ICA impinging on nasal visual field fibers that do not decussate in chiasm
. Difficult to detect due to binocular vision

Question 11

Optic tract lesion

Answer 11

. Contralat. Homonymous hemianopsia
. Loss of uncrossed nasal visual field fibers and decussate temporal visual fibers
. If lesion is proper to branching of projections to visual reflexes the pupillary reflex will be absent
. If lesion occurs after reflex projections have branched or in LGN the pupillary reflex will remind intact

Question 12

Optic radiations lesions

Answer 12

. Contralat. Homonymous hemianopsia
. Loss of all fibers in optic radiations (rare)
. Pupillary reflex remains intact

Question 13

Meyer’s loop lesion

Answer 13

. Contralat. Sup. Quadrantanopsia

. Loss of optic radiation that course most ant. Through temporal lobe

Question 14

Parietal portion of optic radiations lesion

Answer 14

. Loss of radiations through parietal lobe

. Contralat. Inf. Quadrantanopsia

Question 15

Unilateral lesion of primary visual cortex

Answer 15

. Contralat. Homonymous hemianopsia w/ macular sparing
. Cause: occlusion of PCA or its calcarine a. Branch
. Macular sparing due to disproportionately large representation of macula in primary visual cortex and presence of collateral circulation from MCA