Pupils Flashcards
What is mydriasis?
Widening of the pupil
What is miosis?
Constriction of pupil
What is anisocoria?
The condition of one pupil being more dilated than the other
What muscle is responsible for pupillary dilatation?
The radial muscle
What nervous system controls the radial muscle?
SNS- activation –> pupillary dilatation (fight or flight- advantageous to see more if running away from predator etc)
What muscle is responsible for pupillary constriction?
The circular muscle
What nervous system controls the circular muscle?
PNS
Where is the afferent limb of the pupillarylight reflex?
Within CN II
Where is the efferent limb of the pupillary light reflex?
WIthin CN III
What nuclei are involved in the pupillary light reflex?
Pretectal
Edinger-Westphal
Describe the pathway involved in pupillary light responses
- Afferent: Optic nerve –> lateral geniculate body –> pretectum (midbrain)
- Efferent: Edinger-Westphal nucleus (midbrain) –> oculomotor nerve
What are the signs and symptoms of Horner’s syndrome?
Partial ptosis
Enophthalmos
Anhydrosis
Small pupil (miosis)
What is the pathology causing Horner’s syndrome?
Interruption of the sympathetic pathway starting at the hypothalamus
Will the pupillary reflexes (light and accommodation) be impaired in Horner’s syndrome?
No, however there is reduced or delayed dilatation of the eye due to interruption of the sympathetic pathway pupillodilator muscles.
What are the causes of Horner’s syndrome?
- Central:
- Demyelination e.g. MS
- Brainstem or sc tumour or haemorrhage/infarct
- Pre-ganglionic:
- Pancoast’s tumour: T1 nerve root lesion
- Trauma: Central venous catheterisation or carotid endarterectomy
- Neck surgery (thyroid or laryngeal)
- Post-ganglionic:
- Cavernous sinus thrombosis: Associated with CN 3,4, 5 and 6 palsies.
- Herpes zoster