Eye Movements, Pupils, and Vision

posterior communicating artery (PCOM)

An aneurysm of the ________ can result in a compressive injury to CN III.

Compressive

_____ injuries to CN III can result in mydriasis but normal eye movements.

Ischemic

______ injuries (diabetic infarct) to CN III can result in diplopia but normal pupils.

horizontal

The _____ gaze center is located in the pons at the level of the facial colliculus

Vertical

The _____ gaze center is located in the midbrain; compressed in Parinaud syndrome (pineal tumor; vertical gaze palsy, obstructive hydrocephalus)

Sunset sign

damage to vertical gaze center; patient has paralysis of upgaze and eyes appear to look downward with pupils partially covered by lower eyelids

Intranuclear ophthalmoplegia (INO)

characterized by an eye that fails to adduct on testing of horizontal gaze despite normal convergence (and PERRLA). This results from injury to the IPSILATERAL (IL to eye with impaired adduction) medial longitudinal fasciculus (MLF)

Medial longitudinal fasciculus

This is a mixed tract, carrying both ascending and descending axons, but the MLF carries intranuclear axons between the abducens nucleus and the oculomotor nucleus to couple the IL medial and CL lateral rectus muscles for horizontal gaze. This is commonly affected in MS and medial pontine syndromes

One-and-a-half syndrome

results from injury to both right and left MLFs and one abducens nucleus (See Caudal Medial Pontine Syndrome). This syndrome is characterized by, on testing of horizontal gaze, one eye that can only abduct and the other eye that cannot abduct or adduct.

Anisocornia

(unequal pupils) can be caused by: CN III (mydriasis), sympathetics (miosis), physiological (10% of patients)

Argyll-Robertson pupil

seen in tabes dorsalis (but also in diabetes and Lyme disease) and is characterized by small, irregular pupils that constrict on accommodation but have a weak or absent pupillary light reflex (light-near dissociation – pupils don’t respond to light); often referred to as prostitute’s pupil because of the association with syphilis and that the pupils accommodate but don’t react; believed to be caused by damage/interruption to the circuit from the retina → pretectal nucleus → Edinger-Westphal

Tonic (Adie) pupils

Pupils (usually bilateral) are slightly enlarged in ambient light, but constrict slowly and incompletely to direct light; respond normally to accommodation but once constricted, the pupil is tonic – it redilates very slowly; believed to be caused by damage to postganglionic parasympathetic axons (cell bodies in ciliary ganglion)

Same

With visual pathway lesions pupils are [same/different] size

Retina or optic nerve

lesion to ______ results in ipsilateral blindness/blind spot; scotoma (multiple sclerosis)

Midline optic chiasm

Lesion to _____ results in bitemporal hemianopsia (pituitary tumor)

Tiny

A ____ lesion to the lateral optic chiasm (aneurysm) will result in ipsilateral hemianopsia

Big

A ____ lesion to the lateral optic chiasm (aneurysm) will result in IL scotoma + hemianopsia

Optic tract

Lesion to _____ results in contralateral homonymous hemianopsia (anterior choroidal artery infarct) and an afferent pupillary defect in the CL eye. The pupillary defect is in the eye with vision loss in the temporal field

lateral geniculate body (LGB)

Lesion to _____ results in contralateral homonymous hemianopsia (thalamic hemorrhage or infarct (PCA)

visual cortex

Lesion to _____ results in contralateral homonymous hemianopsia with macular sparing (PCA infarct, macular sparing results from collateral supply of the visual cortex from the middle cerebral artery)

Entire optic radiation

Lesion to _____ results in contralateral homonymous hemianopsia (MS, tumor). There are no pupillary axons in the lateral geniculate or optic radiations – lesion in these locations result in vision loss, but no afferent pupillary defect

Meyer’s Loop

Lesion to _____ results in contralateral quadrantanopia (“pie in the sky”; inferior division MCA infarct)

Marcus Gunn Pupil

(afferent pupillary defect) = observed with lesion to the retina (infarct) or optic nerve (multiple sclerosis) and with the swinging light test: shine light in bad eye = no pupillary response in either eye; shine light in good eye = both pupils constrict; move light from good eye to bad eye = both pupils dilate (i.e. they dilate because the good eye is experiencing a decrease in the amount of light than with it shown directly into the eye and the bad eye cannot detect any light)