The Eye Flashcards
role of lacrimal gland
produce secretions (tears) that lubricate, clean and protect the surface of the anterior eye
route of tears
pass medially over the eye towards the puncta on upper and lower eyelids where they drain down the nasolacrimal duct which passes through the skull into the nasal cavity
role of anterior eye
protect sensitive inner eye and focus and funnel light inwards
what is the cornea?
transparent layer over iris and pupil
transparent layer of eye
cornea
role of cornea
light enters the eye
white of the eye
sclera
sclera role
tough outer protective layer
gives shape to eyeball
sclera is covered by what?
conjunctiva
conjunctiva
transparent mucous membrane covering the sclera and internal eyelid
doesn’t cover cornea
bulbar conjunctiva
(superficial to sclera (on top of))
○ Protective
○ Small blood vessels
(palpebral conjunctiva)
○ Continuous with the bulbar conjunctiva
○ Makes the conjunctival fornix (fold)
common damage to conjunctiva
inflammation and infection - conunctivitis
Palpebral fissures
gap between the upper and lower eyelids (where the eyeball is)
- Palpebri = eyelids
Where the palpebral fissures meet in the corner of the eyes are called…
the canthus/palpebral commissures:
○ Medial canthus/palpebral commissure (inner corner of eye).
○ Lateral canthus/palpebral commissure (outer corner of eye).
Epicanthic fold
fold of skin upon the canthus
CN for sclera
CNI
nutrient supply to cornea
aqueous humor
iris
- Pigmented epithelia laying on the lens
- Deep in the cornea
- Diaphragm with a pupil on top
- Iris changes the diameter of the pupil
- Contains intrinsic eye muscles which constrict and dilate the pupil to change its diameter and therefore the amount of light that enters the eye
lens
- Bends and focus light onto the back of the eye
- Acted on by ciliary muscles attached by suspensory ligaments
- Less malleable and more cloudy as you get older (ability to see up close deteriorates)
○ Cloudy = cateracts
cloudy lens indicates…
cateracts
retina
- Has photosensitive cells called rods and cones which detect light and colour respectively
○ Convert light into neural activity which is transmitted via the optic nerve to the occipital lobe- At the centre is the macula focuses the most light and the centre is the fovea (focuses central vision)
centre of retina is…
- At the centre is the macula focuses the most light and the centre is the fovea (focuses central vision)
fluids filling the eye
2 fluids called humors filling the eye and maintain the shape and pressure of the eyeball
- Anterior to the lens is the water like one which is aqueous humor
- Gel like vitreous humour posterior
- Pathology of either of these puts pressure on the optic nerve and causes conditions like glycoma
how is diameter of pupil adjusted?
by sphincter and dilated pupillae muscles
what happens to pupil in bright light or to focus on near objects and how?
contraction of sphincter pupillae reduces pupil aperture
what happens to pupil in dark light or in response to fright?
dilator pupillae increases pupil diameter
innervation of sphincter muscles
parasympathetic
innervation of dilator pupillae
sympathetic
shape of lens at rest
bulges
shape of lens when contracted
flattens
what changes the shape of the lens
contraction of the ciliary body causes pulling on the suspensory ligaments attached to the lens
shape change of the lens is called what?
accommodation
what does accommodation allow?
eye to focus on near or far objects by focusing incoming light
where is lens
posterior ro pupil
where is the anterior chamber
between cornea and iris
what is between cornea and iris
anterior chamber
where is posterior chamber
between iris and lens
what is between iris and lens
posterior chamber
what are the anterior and posterior chambers filled with?
aqueous humour
where is aqueous humour produced?
by ciliary body
where does aqueous humour drain
between cornea and sclera
ciliary muscle
ring of smooth muscles surrounding the lens inside the eye
- Autonomic muscle
- Can contract (smaller ring)
○ Zonular fibres relax so lens can shrink and become fact
○ Focus on near objects
- Can relax (larger ring)
○ Fibres under tension and pull the lens thin
○ Focus on distant objects
- Lens sits inside the ring and is strung from it by zonular fibres
- Parasympathetic innervation via cranial nerve 3 - oculomotor nerve
sphincter pupillae
smooth muscle cells in iris
- Contraction causes pupil to be smaller so less light into eye
- Innervated by parasympathetic fibres from cranial nerve 3
- Constriction of the pupil is called miosis
pupillae light reflex
- If lots of light goes into the eye and falls on the retina, this is carried to the midbrain by cranial nerve 2 (optic nerve) and the reflex arc says lots of light is coming in and then the cranial nerve 3 (parasympathetic fibres) tell sphincter pupillae to contract and constrict the pupil so less light goes into the eye.
- Happens to both eyes at the same time regardless of which eye the light is going into
- If cranial nerve 3 is damaged or compressed or if midbrain is injured then the reflex may be absent
- Need 2 muscles: this one does the opposite
○ Dilator pupillae - dilator muscles (smooth muscle cells in the iris)
§ Pull on edge of iris to make pupil bigger to let more light in
§ Innervated by sympathetic fibres - mediated by noradrenaline so the fight or flight response can cause pupil dilation (some drugs can also cause this as they contain noradrenaline)
□ Spinal nerves in chest so damage in chest or neck may affect this function and only on one side maybe.
§ Mydriasis = dilation of the pupil
main chamber of eye
vitreous chamber
vitreous chamber
main chamber of eye lined by retina
lights path through the eye
enters through pupil
projected via lens onto retina where there are Rods and cones
nerve fibres from the retina combine to form an optic nerve in the optic disk (blind spot)
rod cells
in retina
black and white vision
cone cells
in retina
colour vision
retina is supported by…
choroid layer providing oxygenated blood and nutrients via BV
optic nerve innervates the…
optic disk
choroid layer
(posterior to the retina) - rich blood filled layer that stops light bouncing around in the eye
rod and cone cells wiring
Rod and cone cells are wired so that the neurons pass in front but where the nerves join in the optic disk means there is a blind spot
macula lutea
high-res focus area of eye
high-res focus area of eye
macula lutea
central part of macula
fovea
fovea
central part of macula with the highest density of cones
Macula lutea with fovea centralis
centre of focus. (the macula contains the fovea)
which cranial nerves are eye related?
2
3
4
6
fibres from retina converge to create….
CNII - optic nerve
what forms the optic nerve
fibres from retina
optic nerve route
optic nerve travels through optic canal of the orbit tor enter the cranial cavity.
left and right optic nerves join to form the optic chiasm
here, some nerve fibres decussate to opposite side of brain
2 nerve structures again form, a left and right optic tract which pass posteriorly to the lateral geniculate nucleus of the thalamus and project onto occipital lobe where image is processed
where is optic chiasm
posterior to pituitary gland
pituitary tumours and the optic chiasm
tumours can compress the chaism, causing a pattern of visual loss called bitemporal hemianopia
damage at optic chiasm results in…
bitemporal hemianopia
bitemporal hemianopia
damage to optic chiasm
loss of lateral field of vision (see medial vision only)
tunnel vision
damage to optic nerve from one eye results in…
blindness in eye
damage to optic tract results in…
homonymous hemianopia
homonymous hemianopia
damage to optic tract
loss of vision on the same side of each eye
where is the damage if bilndess of the eye is the result
optic nerve of that eye
how many extraocular muscles
6-7
2 types of extraocular muscle
rectus
oblique
rectus muscles
travel straight backwards posteriorly alongside the eye
oblique muscles
more obtuse insertion (rotate eye)
4 rectus muscles
superior
inferior
medial
lateral
2 oblique muscles
superior
inferior
small cinnective tissue that the superior oblique runs through
trochlear
which eye muscle runs through the trochlear
superior oblique
nerve innervating the superior oblique
trochlear nerve (CNIV)
shape of the orbit
conical
direction of eye at rest
forwards
upwards gaze
elevation
downwards gaze
depression
outwards gaze
abduction
inwards gaze
adduction
inward rotation
intorsion
outward rotation
extorsion
superior rectus movement
elevation and adduction
medial rectus movement
adduction
inferior rectus movement
depression
inferior oblique movement
depression and adduction
superior oblique movement
depression and abduction
lateral rectus movement
abduction
muscle for elevation and adduction
superior rectus
muscle for adduction
medial rectus
muscle for depression
inferior rectus
muscle for depression and adduction
inferior oblique
muscle for depression and abduction
superior oblique
muscle for abduction
lateral rectus
nerve innervation for superior rectus
oculomotor
nerve innervation for medial rectus
olucomotor
nerve innervation for inferior rectus
oculomotor
nerve innervation for inferior oblique
oculomotor
nerve innervation for superior oblique
trochlear nerve
nerve innervation for lateral rectus
abducens nerve
oculomotor nerve innervates which eye muscles
superior, medial and inferior rectus
inferior oblique
trochlear nerve innervates which eye muscles
superior oblique
abducens nerve innervates which eye muscles
lateral rectus
what is conjugate eye movement?
e.g. as one eye adducts, the other abducts simultaneously
3 ways conjugate eye movement occurs
scanning
tracking
compensation
scanning
from one visual target to another at high speed (saccades)
tracking
eyes follow a slow-moving object across your vision
compensation
eyes remain on target despite body moving
vestibular ocular reflex (VOR)
vestibular ocular reflex (VOR)
compensation - eyes remain on target despite body moving
what are gaze centres/nuclei and what do they do?
found in brainstem (midbrain and pons)
conjugating eye movements
vertical and horizontal gaze centres activated either consciously or automatically
gaze centres in pons
left and right horizontal gaze centre
paramedian pontine reticular formation (PPRF) - signals CN to fire for conjugation
horizontal scanning/saccades
- muscles
- gaze centres
- nerves
medial and lateral rectus muscles on opposite sides are linked
nerves controlling these muscles are wired to each other via horizontal gaze centre
CNIII and CNVI
midbrain and gaze centres
paired upward gaze centre in median longitudinal fasciculus (MLF)
paired downward gaze centre ventral to this
nuclei pair of elevators or depressions conjugate eye movements
automatic scanning/smooth pursuit and the brain
visual info from the eye activates the superior colliculus, which activates the nuclei of corresponding gaze centres to initiate rapid eye movement - accuracy fine-tuned by the cerebellum
voluntary ocular saccades and the brain
frontal eye fields in motor cortex initiate signal for eyes to move (conscious signal)
signal decussates to the opposite, side of the brainstem where it stimulates a gaze centre
tracking and the brain
in addition to gaze centres, other nucleus in pons (nucleus prepositus hypoglossi) triggers head movement
labyrinth and cerebellum fine tune eye movements to keep focus on target
