vision 3+4 Flashcards
what happens at the optic chasm
the nasal retinal fibres decussate - they cross over to the contralateral side
- the temporal retinal fibres do not decussate
what is the temporal half of the visual field detected by
- 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.
where are the nasal halves of the visual fields detected
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.
optic chiasm
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
optic nerve
- 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
lateral geniculate nucleus
- located on posterior surface of thalamus
optic radiation
- also called geniculocalcarine tract
- located in the white matter of cerebral hemispheres
- travels to occipital lobe
visual cortex
- located in occipita lobe
- surrounds calcarine sulcus (located on medial surface)
- receives input from LGN
visual pathway - sensory pathway
- photoreceptors - Rods and cones Detect light
Become activated andPass info to bipolar cells - bipolar cells - 1st order neurons
- ganglion cells - 2nd order
- cells of the lateral geniculate body - 3rd order
extraocular muscles
lie outside the eyeball
- trochlea
- superior oblique
- superior rectus
- lateral rectus
- medial rectus
- inferior rectus
- inferior oblique
superior rectus
origin: annulus of Zinn
insertion - superior anterior sclera
primary action - elevation
secondary action - intorsion, adduction
inferior rectus
origin: annulus of Zinn
insertion - inferior anterior sclera
primary action - depression
secondary action - extorsion, adduction
medial rectus
origin: annulus of Zinn
insertion - medial anterior sclera
primary action - adduction
lateral rectus
origin: annulus of Zinn
insertion - lateral anterior sclera
primary action - abduction
superior oblique
origin: body of sphenoid
insertion - superior posterolateral sclera
primary action -intorsion
secondary action - abduction depression
inferior oblique
origin: anterior oblique
insertion - inferior posterolateral sclera
primary action - extortion
secondary action - abduction, elevation
Annulus of Zion
thickening of periosteum surrounding optic canal and superior orbital fissure
muscles of the eyebrow
occipitofrontalis
procerus
orbicularis oculi
corrugator supercillaris
occipitofrontalis
raises brow
- origin - highest nuchal line occipital bone
- insertion - epicranial aponeurosis
procerus
pulls medial brow inferiorly
- origin - nasal bone
- insertion - medial side frontalis
orbicularis oculi
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
corrugator supercillaris
pulls brow medially
- origin - superciliary arch on frontal bone
insertion - skin medial eyebrow
what are all the brow muscles innervated by
cranial VII
features of the medial canthus
medial caruncle - modified skin
plica semilunaris -fold of the conjuctiva - allows full lateral movement of globe
conjunctiva
- Conjunctiva is A mucous membrane that stretches across the anterior aspect of the eyeball
eyelid components
- skin - most superficial
- subcutaneous tissue
- orbicularis oculi
- tarsal plate
- tarsal muscle (smooth)
- conjunctiva - most deep
tarsal plates
- strengthened bands of connective tissue
- provide structure and shape
tarsal glands
- sebaceous glands
- secrete outer layer of tear film
palpebral ligaments
medial logament attaches onto lacrimal crest
lateral ligament attaches onto zygomatic bone
lacrimal apparatus
apparatus associated with tears
- sac
- puncta
- canaliculi
- nasolacrimal duct
lacrimal apparatus - sac
- sits in lacrimal fossa
- composed of fibroelastic tissue
- medial palpebral ligament straddles sac
lacrimal apparatus- puncta
- tear drainage holes
- located on lacrimal papillae
lacrimal apparatus - nasolacrimal duct
- delivers tears into the inferior nasal meatus
- valve prevent reflux of tears into duct
lacrimal apparatus - canaliculi
tubes that drain tears from puncta into lacrimal sac
- walls contain elastic tissue
- surrounded by fibres of OO
composition of the tear film
oil on top then water then mucin
oil in tear film
produced by the tarsal, sweat and sebaceous glands
- 0.2-0.9 micrometres thick
- stops watery layer from evaporating
- enables smooth eye movements
water in tear film
- produced by the lacrimal gland
- 6.5-7.5 micrometres thick
- protects against infection (due to presence of beta lysin, immunoglobulins and lysozyme)
mucin in tear film
- produced by the conjunctival goblet cells
- 0.5 micrometres
- wets microvilli of corneal epithelium
- helps adhesion of tears to ocular surface
- traps bacteria/ dirt
ophthalmic artery
Branch of the internal carotid artery
- Comes off just lateral to the optic chiasm
long and short posterior ciliary arteries
- shorts ones anastomose to form the ring of Zion
