vision 3+4

Question 1

what happens at the optic chasm

Answer 1

the nasal retinal fibres decussate - they cross over to the contralateral side

• the temporal retinal fibres do not decussate

Question 2

what is the temporal half of the visual field detected by

Answer 2

• detected by the nasal half of the retina
• that information then travels from the nasal part of the retina down the optic nerve to the optic chiasm
• at the optic chiasm the nasal retinal fibers Decussate ( they cross over to the contralateral side)
• Then from there it’s the usual path. So they’ll go in the optic tract to the lateral geniculate nucleus, then through the optic radiation go to the visual cortex in the occipital part of the brain.

Question 3

where are the nasal halves of the visual fields detected

Answer 3

the nasal halves of the visual fields are detected on the temporal half of the retina on the left and right side.

- From here the information travels down the optic nerve.
- And it gets to the optic chiasm but these red fibres do not cross over so they don't decussate. They remain ipsilateral
- and from there We'll go through the usual lgn, optic radiation and then brain.

Question 4

optic chiasm

Answer 4

lies within the circle of Willis
- inferior to the chiasm is the pituitary gland
- superior to the chiasm is the 3rd ventricle
- nasal optic nerve fibres travel contralaterally here

Question 5

optic nerve

Answer 5

• subarachnoid space surrounding it is continuous with intracranial subarachnoid space
• fibres only become myelinated after going through lamina cribrosa
• exits orbital cavity through optic canal

Question 6

lateral geniculate nucleus

Answer 6

• located on posterior surface of thalamus

Question 7

optic radiation

Answer 7

• also called geniculocalcarine tract
• located in the white matter of cerebral hemispheres
• travels to occipital lobe

Question 8

visual cortex

Answer 8

• located in occipita lobe
• surrounds calcarine sulcus (located on medial surface)
• receives input from LGN

Question 9

visual pathway - sensory pathway

Answer 9

1. photoreceptors - Rods and cones Detect light
   Become activated andPass info to bipolar cells
2. bipolar cells - 1st order neurons
3. ganglion cells - 2nd order
4. cells of the lateral geniculate body - 3rd order

Question 10

extraocular muscles

Answer 10

lie outside the eyeball
- trochlea
- superior oblique
- superior rectus
- lateral rectus
- medial rectus
- inferior rectus
- inferior oblique

Question 11

superior rectus

Answer 11

origin: annulus of Zinn
insertion - superior anterior sclera
primary action - elevation
secondary action - intorsion, adduction

Question 12

inferior rectus

Answer 12

origin: annulus of Zinn
insertion - inferior anterior sclera
primary action - depression
secondary action - extorsion, adduction

Question 13

medial rectus

Answer 13

origin: annulus of Zinn
insertion - medial anterior sclera
primary action - adduction

Question 14

lateral rectus

Answer 14

origin: annulus of Zinn
insertion - lateral anterior sclera
primary action - abduction

Question 15

superior oblique

Answer 15

origin: body of sphenoid
insertion - superior posterolateral sclera
primary action -intorsion
secondary action - abduction depression

Question 16

inferior oblique

Answer 16

origin: anterior oblique
insertion - inferior posterolateral sclera
primary action - extortion
secondary action - abduction, elevation

Question 17

Annulus of Zion

Answer 17

thickening of periosteum surrounding optic canal and superior orbital fissure

Question 18

muscles of the eyebrow

Answer 18

occipitofrontalis
procerus
orbicularis oculi
corrugator supercillaris

Question 19

occipitofrontalis

Answer 19

raises brow
- origin - highest nuchal line occipital bone
- insertion - epicranial aponeurosis

Question 20

procerus

Answer 20

pulls medial brow inferiorly
- origin - nasal bone
- insertion - medial side frontalis

Question 21

orbicularis oculi

Answer 21

lowers brow
- sphincter muscle of the eye
- can only blink due to this muscle
- origin: palpebral: medial palpebral ligament
orbital: medial palpebral ligament and bone
- insertion: palpebral: lateral palpebral raphe
orbital: loops to origin

Question 22

corrugator supercillaris

Answer 22

pulls brow medially
- origin - superciliary arch on frontal bone
insertion - skin medial eyebrow

Question 23

what are all the brow muscles innervated by

Answer 23

cranial VII

Question 24

features of the medial canthus

Answer 24

medial caruncle - modified skin

plica semilunaris -fold of the conjuctiva - allows full lateral movement of globe

Question 25

conjunctiva

Answer 25

• Conjunctiva is A mucous membrane that stretches across the anterior aspect of the eyeball

Question 26

eyelid components

Answer 26

1. skin - most superficial
2. subcutaneous tissue
3. orbicularis oculi
4. tarsal plate
5. tarsal muscle (smooth)
6. conjunctiva - most deep

Question 27

tarsal plates

Answer 27

• strengthened bands of connective tissue
• provide structure and shape

Question 28

tarsal glands

Answer 28

• sebaceous glands
• secrete outer layer of tear film

Question 29

palpebral ligaments

Answer 29

medial logament attaches onto lacrimal crest
lateral ligament attaches onto zygomatic bone

Question 30

lacrimal apparatus

Answer 30

apparatus associated with tears
- sac
- puncta
- canaliculi
- nasolacrimal duct

Question 31

lacrimal apparatus - sac

Answer 31

• sits in lacrimal fossa
• composed of fibroelastic tissue
• medial palpebral ligament straddles sac

Question 32

lacrimal apparatus- puncta

Answer 32

• tear drainage holes
• located on lacrimal papillae

Question 33

lacrimal apparatus - nasolacrimal duct

Answer 33

• delivers tears into the inferior nasal meatus
• valve prevent reflux of tears into duct

Question 34

lacrimal apparatus - canaliculi

Answer 34

tubes that drain tears from puncta into lacrimal sac
- walls contain elastic tissue
- surrounded by fibres of OO

Question 35

composition of the tear film

Answer 35

oil on top then water then mucin

Question 36

oil in tear film

Answer 36

produced by the tarsal, sweat and sebaceous glands
- 0.2-0.9 micrometres thick
- stops watery layer from evaporating
- enables smooth eye movements

Question 37

water in tear film

Answer 37

• produced by the lacrimal gland
• 6.5-7.5 micrometres thick
• protects against infection (due to presence of beta lysin, immunoglobulins and lysozyme)

Question 38

mucin in tear film

Answer 38

• produced by the conjunctival goblet cells
• 0.5 micrometres
• wets microvilli of corneal epithelium
• helps adhesion of tears to ocular surface
• traps bacteria/ dirt

Question 39

ophthalmic artery

Answer 39

Branch of the internal carotid artery
- Comes off just lateral to the optic chiasm

Question 40

long and short posterior ciliary arteries

Answer 40

• shorts ones anastomose to form the ring of Zion