The Visual Pathway and Eye Muscles

Question 1

What is your visual field?

Answer 1

Everything you see with one eye including the periphery

Question 2

How is visual field tested?

Answer 2

Confrontation test (outpatient screening) or automated perimetry

Question 3

How are images of objects seen in field of vision?

Answer 3

Upside down and inverted
Left half of visual field seen on right part of eye and right half seen on left side

Question 4

Where do all fibres of the eye pass through?

Answer 4

Through optic nerve into optic chiasma

Question 5

What happens to the fibres at the optic chiasma?

Answer 5

Medial nasal fibres cross to opposite side

Question 6

What fibres does the optic tract contain?

Answer 6

Fibres from lateral temporal half of ipsilateral eye and crossed over nasal fibres from contralateral eye
Corresponds to all fibres from opposite half of visual field

Question 7

Where do the fibres from the optic nerve synapse?

Answer 7

At LGB - lateral geniculate body of the thalamus

Question 8

What happens after lateral geniculate body?

Answer 8

Optic radiation passes behind internal capsule to reach primary visual cortex in occipital lobe - area 17

Question 9

What happens is right optic nerve is damaged?

Answer 9

Blindness in one eye - right

Question 10

What happens if optic chiasma is disrupted in the middle?

Answer 10

Bitemporal hemianopia - lateral half of eye on both side are blind

Question 11

What happens if right optic tract is damaged?

Answer 11

Homonymous hemianopia - left visual field is affected

Question 12

What happens if optic radiation is damaged?

Answer 12

Contralateral homonymous hemianopia - if right optic tract then left side of both eyes have blindness

Question 13

When do recti muscles arise from?

Answer 13

Apex of orbit from annular fibrous ring

Question 14

Where do recti and oblique muscles insert?

Answer 14

Recti - sclera anteriorly
Obliques - posteriorly

Question 15

What is the origin of superior and inferior oblique muscles?

Answer 15

SO - lesser wing of sphenoid
IO - medial part of orbital floor

Question 16

What are the terms for eye movement?

Answer 16

Elevation, depression, levoversion, dextroversion, dextrodepression, dextroelevation, levodepression and levoelevation
Intorsion and extorsion

Question 17

What does RADSIN stand for?

Answer 17

Recti Adduct and Superior Intortors
SR and IR adduct and SO and IO abduct
SR and SO intorsion

Question 18

What are the actions of individual EOMs influenced by?

Answer 18

Muscles attached along orbital axis not optical so pull eyeball on angle
Oblique muscles are attached at posterior part of sclera - pull posterior part up and down and anterior moves in opposite direction

Question 19

What happens to the obliques when eye is adducted?

Answer 19

Elevate/ Depress

Question 20

What happens to the superior and inferior obliques when eye is abducted?

Answer 20

Elevate/ depress

Question 21

What is strabismus?

Answer 21

Squint which is misalignment of the eyes
Can be esotropia (convergent) or exotropia (divergent)

Question 22

What are the functional consequences of a squint?

Answer 22

Amblyopia and diplopia

Question 23

What is amblyopia?

Answer 23

Lazy eye - brain supresses image of one eye leading to poor vision in eye without pathology - correctable in early years by eye patch to strengthen

Question 24

What is diplopia?

Answer 24

Double vision
Occurs in squints due to nerve palsies

Question 25

Describe the intrinsic muscles of the eye

Answer 25

Ciliaris muscle in ciliary body
Constrictor pupillae in iris at pupillary border
Dilator pupillae radially running muscle in iris
Ciliaris and constrictor are parasympathetic - CNIII
Dilator is sympathetic

Question 26

What does increased illumination cause?

Answer 26

Parasympathetic - both pupils constrict

Question 27

What does decreased illumination cause?

Answer 27

Sympathetic - both pupils dilate

Question 28

Describe the pupillary reflex

Answer 28

In dimly lit room - pen torch in front of one eye to check both are constricting
Swing light to both sides and both should remain constricted

Question 29

Describe the pathway of the light reflex - afferent limb

Answer 29

Fibres to activate pupillary reflex don’t go to LGB but leave optic tract to go to midbrain where IIIn nucleus is situated
Part of IIIn nucleus is Edinger-Westphal nucleus for parasympathetic fibres
Go to EWN of both sides

Question 30

Describe the pathway of the light reflex - efferent limb

Answer 30

From EWN - preganglionic parasympathetic fibres pass through IIIn into orbit
Then parasympathetic fibres synapse in ciliary region
Postganglionic fibres go through short ciliary nerves to constrictor pupillae

Question 31

What is anisocoria?

Answer 31

Pupils are different sizes - ex. Horner’s syndrome or result from injury
Pupils can look normal but act abnormally to light

Question 32

What are common causes of absent or abnormal pupillary reflex?

Answer 32

Diseases of the retina - detachment or degeneration
Diseases of optic nerve - optic neuritis
Diseases of III CN - efferent limb

Question 33

What do you check is patient has IIIn palsy?

Answer 33

Check pupillary reflex - if absent then suspect a cerebral artery aneurysm which is an emergency
Medical cause like diabetes usually has no effect on parasympathetic fibres

Question 34

Describe Horner’s Syndrome

Answer 34

Anisocoria due to damage of sympathetic innervation of the pupil
Symptoms - ptosis on affected side, miosis, anhidrosis (loss of sweating on affected side)

Question 35

What can be causes of Horner’s syndrome?

Answer 35

Disruption - thoracolumbar outflow, sympathetic chain and cervical ganglion, postganglionic sympathetic fibres travel along blood vessels in head and neck