10 - Visual System 4: Pupillary Reflex Pathways Flashcards
What is the primary visual/geniculostriate pathway?
Retina > LGN > optic radiations > primary visual cortex (perception of vision).
What is the eye movement pathway?
Retina > superior colliculus > pulvinar >parieto-occipital cortex > CN nuclei of extraocular muscles (visual attention)
What are the three pupillary reflexs?
Direct and consensual light reflex (parasympathetic) Accomodation reflex (parasympathetic) Pupil dilation pathway (sympathetic)
What is the afferent limb, the central pathway, and the efferent limb of the direct and consensual light reflexes?
Afferent limb: CN II through bilateral retinal ganglion cells. Central pathway: midbrain bilateral pre-tectal areas Efferent limb: CN III - Edinger westphal nucleus > ciliary ganglia > sphincter pupillae
What is a consensual light reflex?
Shining a light in one eye also causes the other eye’s pupil to constrict.
Describe the anatomy of the oculomotor nerve? What insults do and don’t affect this?
Parasymp fibers are located peripherally in CN III; therefore compression lesions such as aneurysms preferentially affect these parasympathetic fibers. Blood vessels supplying CN III are located centrally, therefore ischemic lesions can spare the parasympathetic fibers.
What three reflexes are used to determine coma and brain death?
Corneal reflex: CN V sensory and CN VII motor. Pupillary light reflex: bilaterally unreactive pupils usually occur because of direct midbrain lesions or midbrain lesions secondary to compression by a supratentorial mass or herniation (drug overdose and hypothermia can mimic this). Vestibuloocular reflex (VOR).
What is the accommodation reflex? What type of stimulus is this used for?
- Pupil constriction - sphincter pupillae contracts 2. Lens accommodation - ciliary muscles contract 3. Eyes converge - medial rectus muscles contract Used for stimulus moving closer to the eyes. To keep focused you want pupil constriction for acuity and lens accommodation and convergence to maintain foveation.
What is the light vs. Accommodation reflex pathway?
AFFERENT: 1. Perception of object by visual cortex to retinal ganglion cells bilaterally 2. LGN via optic radiations to primary visual cortex 3. Visual associated cortices 4. Midbrain reticular formation (*accommodation center*) projects to the edinger westphal nucleus EFFERENT: 5. Edinger westphal causes changing of lens shape and accommadation. Oculomotor causes convergence of the eyes.
What is Argyll Robertson Pupil?
ARP: Accommodation Reflex Present, Pupillary (light) Reflex Absent Rare; associated with neurosyphillis or tumors that impinge on the third ventricle.
What are the afferent and efferent portions of the pupillary dilation reflex? Is this sympathetic or parasympathetic?
Afferent: perception of object by visual cortex goes to the hypothalamus Efferent: 1. Regulatory nuclei in hypothalamus to lateral horn of spinal cord 2. Superior cervical ganglion to internal carotid plexus 3. Long and short ciliary nerves to the dilator pupillae. Sympathetic.
What is horners syndrome? What are the three potential causes?
Miosis (pupil constriction), ptosis (drooping eyelids), anhidrosis (lack of sweating), erythematosis (blushing). Pancoast tumor of apical lung. First neuron from hypothalamus can be injured by a brainstem stroke that causes horners. Third neurons from the internal carotid plexus can be affected by an aneurysm.
What is aniscoria?
Pupil asymmetry. Can be benign or pathological.
What would you expect to see in ambient light, a dark room, light in the left eye, and light in the right eye for someone with a parasympathetic lesion of the left eye?
Ambient light: Left pupil larger than right (anisocoria)
Dark room: Left pupil does not appear to dilate further
Light in the left eye: Left eye is detecting the light stimulus becasue there’s a consensual constriction in the right eye. But the left eye is still dilated when the light is on it showing that the direct light reflex is abnormal.
Light in the right: Right eye is detecting the light stimulus normally, but the consensual light refles in the left eye is abnormal and it does not constrict.
What would you expect to see in ambient light, a dark room, light in the left eye, and light in the right eye for someone with a left afferent pupillary defect (Marcus Gunn pupil)?
Ambient light: pupils are normal
Dark room: both dilate, sympathetic system functioning normally
Light in the Left eye: Left eye ability to sense the signal is reduced; minimal pupil constiction.
Light in right eye: Right eye is detecting light stimulus, normal response. Consensual reflex is normal and Left eye constricts.
What would you expect to see in ambient light, a dark room, light in the left eye, and light in the right eye for someone with a left Horner’s Syndrome?
Ambient light: Right pupil larger than the left (anisocoria)
Dark room: Right dilates, left does NOT dilate (sympathetic not functioning normally)
Light on Left eye: Left eye constricts because it is detectin the stimulus. For the consensual reflex, the right eye is not as consticted as the left eye.
Light on right eye: Right eye has normal response. Left eye isn’t as constricted as the right.
