Pupil Flashcards
What is the diameter of the pupil?
Dilated 9mm
Constricted 2mmW
here is the pupil situated?
Slightly inferonasally
What is hippus?
Physiological tremor of the pupil
What happens when light intensity increases?
Up to 9 log units, stregth and duration of puillary contraction increases and latency period decreases
At intensity above 9 log units, pupillary response plateaus
What is purkinje shift?
Pupil constriction occurs in response to light of any colour but the reposnse is related to the apparent brightness
What effect does dilation have on depth of focus, depth of field?
Decreased depth of focus and depth of field with larger pupil
Decreased diffraction
Small pupil causes greater depth of focus, decreased chromatic aberration but also increase in diffraction
What is the stiles crawford effect?
Light entering eye at edge of pupil is less effective at stimulating photoreceptors than light entering at centre as it enters at an oblique angle
Light entering from periphery increases with mydriasis
What happens in dilation to chromatic aberration
Diffraction of light decreases with wider pupil and so chromatic aberration increases
What do you get in an efferent pupillary defect
Fixed dilated pupil
What are causes of efferent defect?
Brainstem lesion at level of superior colliculus and red nucleus
Fascicular third nerve lesions
Compressive third nerve lesions
Lesions of the cilairy ganglion or short ciliary nerves
Iris damage secondary to previous surgery or grossly elevated IOP
Drugs - inadvertent exposure to mydriatic agent such as atropine (pilocarpine ineffective on mydriatic agent dilated pupil)
What stimulates mydriasis?
Contraction of dilator pupillae
Stimualted by noradrenergic sympathetic nerves that pass through the ciliary ganglion
Sympathomimetic agents cause dilation
What do cholinergic agonists cause?
Constriction of the pupil miosis by stimulating sphincter muslce
How does coaine exert mydraitic effect
Prevent noradrenaline reuptake
What are duration of action of mydraitics, anticholinergics
Tropicamide - 6 hours
Cyclopentolate - 12 hours
Homatropine - 2 days
Atropine - days
How does diamorphine afafect pupil
Miosis by reducing cortical inhibition of edinger-westphal nucleus -
What effect does nicotine and alcohol have on pupil
Mydriasis
How does miosis occur?
Stimualtion of sphinter pupillae via cholinergic postganglionic parasympathetic neurones from the ciliary ganglion
How does carbachol cause miosis? Physostigmine? Thymoxamine?
Carbachol increases ACh release
Physostigmine/edrophonium inhibit AChesterase
Thymoxamine is an alpha blocker taht paralyses dilator pupillar
What is honer’s syndrome?
Miosis, partial ptosis, anhidrosis and enophthalmos
Interruption of sympathetic chain
What occurs in postganglionic horner’s sydnrome?
Normal facial sweating as they travel on the ECA not ICA
What are preganglionic causes of Horners
Pancoast lung tumour
How to test for Honers?
cocaine has nor effect on Horner’s pupil
Hydroxyamphetamine will dilate pregnalgionic Horner if postganglionic pathway is intact
What happens in Argyll Robertson pupil
Accommodates but does not react to light
Small pupils - do not dilate with atropine
Causes syphylis tabes dorsalis
Diabetes
What happesn in Adie’s Holme pupil
Light reaction is sluggish
Accommodation strong and tonic
Supersensitvity to cholinergics
Cilairy ganglion lesion
