Pupil

Question 1

What is the diameter of the pupil?

Answer 1

Dilated 9mm
Constricted 2mmW

Question 2

here is the pupil situated?

Answer 2

Slightly inferonasally

Question 3

What is hippus?

Answer 3

Physiological tremor of the pupil

Question 4

What happens when light intensity increases?

Answer 4

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

Question 5

What is purkinje shift?

Answer 5

Pupil constriction occurs in response to light of any colour but the reposnse is related to the apparent brightness

Question 6

What effect does dilation have on depth of focus, depth of field?

Answer 6

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

Question 7

What is the stiles crawford effect?

Answer 7

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

Question 8

What happens in dilation to chromatic aberration

Answer 8

Diffraction of light decreases with wider pupil and so chromatic aberration increases

Question 9

What do you get in an efferent pupillary defect

Answer 9

Fixed dilated pupil

Question 10

What are causes of efferent defect?

Answer 10

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)

Question 11

What stimulates mydriasis?

Answer 11

Contraction of dilator pupillae
Stimualted by noradrenergic sympathetic nerves that pass through the ciliary ganglion

Sympathomimetic agents cause dilation

Question 12

What do cholinergic agonists cause?

Answer 12

Constriction of the pupil miosis by stimulating sphincter muslce

Question 13

How does coaine exert mydraitic effect

Answer 13

Prevent noradrenaline reuptake

Question 14

What are duration of action of mydraitics, anticholinergics

Answer 14

Tropicamide - 6 hours
Cyclopentolate - 12 hours
Homatropine - 2 days
Atropine - days

Question 15

How does diamorphine afafect pupil

Answer 15

Miosis by reducing cortical inhibition of edinger-westphal nucleus -

Question 16

What effect does nicotine and alcohol have on pupil

Answer 16

Mydriasis

Question 17

How does miosis occur?

Answer 17

Stimualtion of sphinter pupillae via cholinergic postganglionic parasympathetic neurones from the ciliary ganglion

Question 18

How does carbachol cause miosis? Physostigmine? Thymoxamine?

Answer 18

Carbachol increases ACh release
Physostigmine/edrophonium inhibit AChesterase
Thymoxamine is an alpha blocker taht paralyses dilator pupillar

Question 19

What is honer’s syndrome?

Answer 19

Miosis, partial ptosis, anhidrosis and enophthalmos

Interruption of sympathetic chain

Question 20

What occurs in postganglionic horner’s sydnrome?

Answer 20

Normal facial sweating as they travel on the ECA not ICA

Question 21

What are preganglionic causes of Horners

Answer 21

Pancoast lung tumour

Question 22

How to test for Honers?

Answer 22

cocaine has nor effect on Horner’s pupil

Hydroxyamphetamine will dilate pregnalgionic Horner if postganglionic pathway is intact

Question 23

What happens in Argyll Robertson pupil

Answer 23

Accommodates but does not react to light

Small pupils - do not dilate with atropine

Causes syphylis tabes dorsalis
Diabetes

Question 24

What happesn in Adie’s Holme pupil

Answer 24

Light reaction is sluggish
Accommodation strong and tonic

Supersensitvity to cholinergics

Cilairy ganglion lesion

Question 25

What does accommodation occur in repsonse to?

Answer 25

Blur (e.g if myopic lens placed infront of eye)
Convergence (e.g. base out prism)

Question 26

What is the power of accommodation at rest

Answer 26

1.5 D
Tonic accommodation

Question 27

What are ciliary msucles?

Answer 27

Smooth msucle arranged longitudinally, radially and circularly

Contraction by parasympathetic innervation by M3 muscarinic receptors

Relaxation by sympathetic adrenergic beta 2 receptors

Question 28

How do cyclopegics work?

Answer 28

Competitively bind M3 receptors in ciliary muscles but block them blcoking accommodation

Question 29

Innervation of ciliary msucle for accommodation?

Answer 29

Parasympathetic from Edingerwestphal nucleus - ciliary ganglion - short ciliary nerves

Question 30

Pathway of light reflex

Answer 30

REtinal ganglion cells
Opic nerves
Optic chiasm (nasal fibres decussate)
Pretectal nuclei of dorsal midbrain (each from both eyes)
Edinger-Westphal nuclei
Parasympathetic fibres for pupillary constriction travel with CNIII to ipsilateral ciliary ganglion
Pupillary sphincter muscles via short ciliary nerves

Question 31

Ho

Question 32

How does light and near reflex differ?

Answer 32

Afferent is first processed in striate cortex (17) , preoccipital cortex (19 and 22)
Nerve pathways for three components of near merge in midbrain at Edinger westphal
Pathway bypasses pretectal nuclei of dorsal midbrain - this results in dichotomy between light and near.
Third cranial nerve and ciliary ganglion