Vision lectures Flashcards
what is refraction?
when light rays bend to form a sharp image on the retina
what is accommodation?
the changes occurring in both eyes as it changes focus from a distant to a close object
what causes refractive errors?
when there is a mismatch between how much we bend light rays in each eye
what are the refractive media in the eyeball?
cornea
aqueous humor
lens
vitreous humor
what does the eye need to do when an object is closer to you to maintain a clear image on the retina?
needs to bend light rays more
what 3 processes occur simultaneously that comprise accommodation?
lens changes shape to become more spherical and thicker
pupil constricts
eyes converge
how does the lens thicken during accommodation?
1/ ciliary muscle contracts making the ciliary body bulge space in the middle decreases suspensory ligaments become lax lens is no longer under stretch lens becomes thicker
what muscle causes the pupil to constrict?
sphincter pupillae
what branch of the autonomic nervous system innervates the sphincter pupillae?
parasympathetic
where is the sphincter pupillae located?
around the border of the pupil
what muscles are responsible for the eyes converging during accommodation?
medial rectus muscles
what is myopia?
short sightedness
what is hyperopia?
long sightedness
what is astigmatism?
non spherical curvature of cornea (or lens)
what is presbyopia?
long sightedness of old age
what is the most common cause of myopia?
eyeball too long
what are symptoms of myopia?
divergent squint in infants
headaches, complain of not being able to see blackboards/distant objects
how is myopia corrected?
bending power is decreased using biconcave lenses:
spectacles
contact lenses
laser eye surgery
what is the most common cause of hyperopia?
eyeball too short or cornea + lens too flat
what objects appear hazy in astigmatism?
both close and distant objects
why does the chance of developing long sightedness increase with old age?
lens gets less mobile/elastic so when the ciliary muscle contracts it is not as capable of changing shape as it was before
what is phototransduction?
conversion of light energy to an electrochemical response by photoreceptors
what do rods and cones have to do in order to illicit an electrochemical response?
activate optic nerve neurons (generate an action potential)
what visual pigment is integrated in the lamellae of rods?
rhodopsin
what visual pigments are integrated in the lamellae of cones?
opsins S, M and L
what type of protein is rhodopsin?
integral transmembrane helical protein
what is the chromophore of rhodopsin formed from?
vitamin A
what happens when light forms on the 11-cis retinal?
it isomerises to all trans retinal
what happens to photoreceptors in the dark?
the are kept depolarised by open sodium/calcium channels
what happens in the phototransduction cascade when the Na+ channels close?
there is RELATIVE hyperpolarisation of photoreceptor cells
how are the photoreceptor cells truly hyperpoolarised?
flux of Ca+ ions to the synapse with bipolar cell, which ultimately stimulates the retinal cell
what will happen in any condition that affects vitamin A absorption?
vision will be affected, possibly leading to blindness. there will also be abnormal conjunctiva and corneal epithelium
what can corneal melting lead to?
future opacification of the cornea
what is the function of the intrinsic ocular muscles?
control pupil diameter and helps alter lens curvature to enable us to see near objects
what is the function of the extrinsic muscles of the eye?
they move the eye
what are the 4 straight muscles of the eye?
medial rectus
lateral rectus
inferior rectus
superior rectus
what are the 2 oblique muscles of the eye?
superior oblique
inferior oblique
where do the recti muscles arise from?
the apex of the orbit from an annular fibrous ring
where does the superior oblique muscle arise from?
the roof of the orbit posteriorly
where does the inferior oblique muscle arise from?
floor of the orbit anteriorly
what muscle elevates the eyelid?
levator palpebrae superioris
where does the LPS lie?
above the superior rectus
what nerve supplies everything except the superior orbit and the lateral rectus muscle?
oculomotor nerve
what does the trochlear nerve supply?
superior orbit
what does the abductent nerve supply?
lateral rectus
where does the LPS muscle originate?
roof of orbit
where do all recti muscles originate from?
tendinous ring
where does the superior oblique originate from?
lesser wing of sphenoid
where does the inferior oblique originate from?
medial part of orbit floor
where do both oblique muscles of the eye insert?
sclera posteriorly
where do all rectus muscles insert?
sclera anteriorly
what is the action of the superior rectus?
elevation when abducted
intorsion when adducted
what is the action of the inferior rectus?
depression when abducted
extorsion when adducted
what is the action of the superior oblique?
depression when adducted
intorsion
abduction
what is the action of the inferior oblique?
elevation when adducted
extorsion
abduction
what are some signs of right third nerve palsy?
drooping eyelid
eye only able to move laterally and slightly downwards
what are some signs of left fourth nerve palsy?
eye moves up when adducted
what are some signs of abducent nerve palsy?
eye being adducted
eye not able to abduct
what is the medical term for a squint?
strabismus
what is esotropia?
manifest convergent squint
what is exotropia?
manifest divergent squint
what is ambylopia?
“lazy eye” where brain supresses the image of one eye leading to poor vision in that eye without any pathology
what is diplopia?
double vision which usually occurs in squints occuring as a result of nerve palsies
what is your visual field?
everything you see with one eye including the periphery
where do all nerve fibres from the eye pass through?
the optic nerve and then to the optic chiasma
where do fibres from the optic tract synapse?
lateral geniculate body of the thalamus
what kind of nerve fibres does the optic tract contain?
fibres from the temporal half of the ipslateral eye and nasal fibres from the contralateral eye
where is the primary visual cortex?
occipital lobe
what does the right visual cortex see?
left half of the visual field and vice versa
what would you expect to happen if the right optic nerve is damaged?
blindness in one eye
what would you expect to happen if the optic chiasma was disrupted in the middle?
bitemporal hemianopia (blindness)
what would you expect to happen if the right optic tract was damaged
left sides of both eyes will be blind
what would you expect to happen if the right optic radiation was damaged?
contralateral homonymous hemianopia
what are the 3 intrinsic eye muscles?
ciliaris muscle
constrictor pupillae
dilator pupillae
what are the ciliaris and constrictor pupillae muscles innervated by?
cranial nerve 3 (parasympathetic)
what is the dilator pupillae innervated by?
plexus around blood vessels (sympathetic)
where do fibres destined to activate the pupillary reflex travel to?
midbrain - to the edinger westphal nucleus of both sides
what is the clinical term for when both pupils are different sizes?
anisocoria
what are the steps in pupillary constriction?
EWN > preganglionic parasympathetic fibres pass through 3rd CN into orbit > parasympathetic fibres go to and synapse in the ciliary ganglion > postganglionic fibres go through short ciliary nerves to constrictor pupillae
all of this leads to pupillary constriction of both sides
what can cause an abnormal/absent pupillary reflex?
diseases of the retina - detachment/degenerations or dystrophies
any abnormality of the afferent limb centre/efferent limb of the reflex
diseases of the optic nerve - optic neuritis
diseases of the 3rd cranial nerve
what is horners syndrome?
anisocoria due to damage to the sympathetic innervation to the pupil
