Vision 2 - The visual pathway

Question 1

what is the visual field?

Answer 1

everything you see with one eye

Question 2

how can you test someones visual field?

Answer 2

confrontation test

automated perimetry

Question 3

is your visual field up right or upside down on your retina?

Answer 3

your visual field is formed upside down and inverted on your retina

Question 4

describe the visual pathway.

Answer 4

light rays enter each eye
travel through the optic nerve
both nasal fibres cross at the optic chasm
the optic tract now contains fibres from temporal half of the ipsilateral eye and the nasal fibres from the contralateral eye
the optic tract then synapses at the LGB
from here optic radiation passes behind internal capsule to reach the primary visual cortex

Question 5

where is the primary visual cortex found?

Answer 5

the occipital lobe

Question 6

where is the LGB found?

Answer 6

its part of the thalamus

Question 7

where is the optic chasm found?

Answer 7

directly onto of the pituitary gland

Question 8

what is the clinical significance of the optic chasm being found onto of the pituitary gland?

Answer 8

if someone has a pituitary tumour, one of the first symptoms is visual disturbances

Question 9

is someones optic nerve got damaged on the right side what would this cause?

Answer 9

blindness in the right eye

Question 10

if the optic chasm got damaged what would this result in?

Answer 10

bilateral hemianopia

Question 11

if the optic tract got damaged on the right side what would this result in?

Answer 11

contralateral homonymous hemianopia

Question 12

if the optic radiation is damaged what would this result in?

Answer 12

contralateral homonymous hemianopia

Question 13

what side of the visual field does the right visual cortex see?

Answer 13

the left side (from both eyes)

Question 14

what is the name for the condition in which there is misalignment of the eyes?

Answer 14

strabismus (squint)

Question 15

what are the different types of strabismus?

Answer 15

esotropia - convergent quint

exotropia = divergent squint

Question 16

how do you test for strabismus?

Answer 16

shine a light in their eyes

the light spot should be equal in both eyes

Question 17

what are the functional consequences of strabismus?

Answer 17

amblyopia (lazy eye)

diplopia (double vision)

Question 18

how does amblyopia occur as a consequence of strabismus and how is it corrected?

Answer 18

the brain suppresses the image of on eye which leads to poor vision without any pathology
corrected by wearing eye patch in early childhood to stimulate the lazy eye

Question 19

how does diplopia occur as a consequence of strabismus?

Answer 19

usually occurs as a result of nerve palsies which cause the strabismus

Question 20

describe the pathway way of fibres which activate the pupillary reflex.

Answer 20

fibres which activate the reflex don’t go to the LGB
they leave the optic tract and enter the midbrain
they stimulate the occulomotor nerve nucleus
part of the nucleus is EWN which has parasympathetic fibres
these parasympathetic fibres pass into the orbit and synapse of ciliary ganglion
post synaptic fibres then go through short ciliary nerves to the constrictor pupillae to constrict it on both side = pupillary reflex

Question 21

in the pupillary reflex, what nerve does the fibres stimulate?

Answer 21

occulomotor nerves nucleus

Question 22

what type of fibres does the pupillary reflex stimulate?

Answer 22

parasympathetic

Question 23

what is the term for pupils that are different sizes and what condition does this occur in?

Answer 23

Aniscoria

Horners syndrome

Question 24

what are the common causes for absent or abnormal pupillary reflex?

Answer 24

diseases of the retina - detachment , degeneration or dystrophies
diseases of optic nerve - optic neuritis (frequently seen in MS)
diseases of the CN III (efferent limb)

Question 25

CN III palsy can occur in which medical condition?

Answer 25

diabetes

Question 26

in CN III palsy due to diabetes, the pupillary reflex is normal, why?

Answer 26

the parasympathetic fibres aren’t damaged so the reflex is normal

Question 27

in someone with CN III palsy due to diabetes, if they didn’t have a pupillary reflex, what would you suspect?

Answer 27

cerebral artery aneurysm = emergency

Question 28

horners syndrome causes what eye abnormality?

Answer 28

aniscoria (pupils different sizes)

Question 29

why does aniscoria occur in corners syndrome?

Answer 29

due to damage of the sympathetic innervation of the pupil

Question 30

what are the main features of Horners syndrome?

Answer 30

aniscoria = pupils different sizes
mitosis (excessive constriction of the affected eye)
ptosis (drooping of the eyelid)
anhidrosis (loss of sweating on the affected side)

Question 31

why could a pan coast tumour of the lung cause horners syndrome?

Answer 31

horners syndrome can occur due to disruption of the sympathetic fibres at any point in the thoracolumbar outflow