Eyes: Reflexes and movement Flashcards
Describe the pupillary light reflex pathway.
Light - retina - rods & cones - ganglion cells
Optic nerve - optic chiasm - optic tract
Pretectal nucleus (midbrain)
Edinger-Westphal nucleus
Oculomotor nerve (III) - ciliary ganglion
Sphincter pupillae muscle
What symptom would result if an Edinger-Westphal nucleus was damaged?
No direct or consensual pupillary light reflex on the damaged side - pupil is dilated and unreactive
What could cause damage to an Edinger-Westphal nucleus?
Midbrain tumour
Marcus-Gunn pupil is a pathology related to which CN?
CN II
What pupillary response will be seen in Marcus-Gunn pupil?
Both pupils will dilate slightly instead of constricting when light is shined in the affected eye
A complete lesion of CN III will result in what eye symptoms?
No direct or consensual pupillary light reflex on the damaged side
Eye is abducted, depressed, and eyelid closed (ptosis)
How do symptoms differ between a CN III compression lesion and a CN III vascular lesion and why?
CN III compression lesion - loss of all functions
CN III vascular lesion - sparing of pupillary functions
The parasympathetic fibres that control the pupil run along the superficial portion of the nerve. In an ischaemic lesion, the core of the nerve is primarily affected, sparing the peripheral fibres
What is the key symptom seen in an Argyll-Robertson pupil?
Pupillary light reflex is absent but accommodation reflex is normal
Which region is damaged in an Argyll-Robertson pupil?
Pretectal region of the midbrain
What is the eye movement called when the eyes track a moving target?
Smooth pursuit
What is the eye movement called when the eyes track from target to target?
Saccadic
Which mechanism stabilises gaze during head movement?
Vestibulo-ocular reflex
What is the medial longitudinal fasciculus?
An interneuron tract that connects the nuclei of CN III, IV, and VI
The medial longitudinal fasciculus enables the eyes to do what?
Move both eyes in the same direction at the same time (conjugate gaze)
Damage to the medial longitudinal fasciculus results in what pathology?
What is the main symptom?
Internuclear ophthalmoplegia (INOP)
When looking left and right only one eye with move, the other remains central
If right-sided eye movement control systems are damaged, in which direction will the eyes drift / look? Why is this?
Drift / look right
Because right-sided control systems make the eyes look left
If left-sided eye movement control systems are damaged, in which direction will the eyes drift / look? Why is this?
Drift / look left
Because left-sided control systems make the eyes look right
