Eye muscles Flashcards
what are the two groups of ocular muscles
intrinsic and extrinsic
what do intrinsic muscles do
control pupil diameter and help alter lens curvature to enable us to see near objects
what do extrinsic muscles do
move the eye (also known as extraoccular muscles or EOMs)
what are the 6 extrinsic muscles that move the eye and one extrinsic muscle that moves the eyelid
4 straight muscles called RECTI:
- medial rectus
- lateral rectus
- inferior rectus
- superior rectus
2 OBLIQUE muscles:
- superior oblique
- inferior oblique
moves eyelid
- Levator palpebrae superioris
where do the recti muscles arise from and insert
the apex of the orbit from an annular fibrous ring
insert at the sclera anteriorly
where does the superior oblique muscle arise from and insert
the roof of the orbit posteriorly (lesser wing of sphenoid
inserts at sclera posteriorly
where does the inferior oblique muscle arise from and insert
the floor of the orbit anteriorly
inserts at sclera posteriorly
what muscle elevates the eyelid
levator palpebra superioris
what is the origin of the LPS and where does it insert
roof of the orbit
inserts into the upper eyelid
what muscle closes the eyelid
obicularis oculi (NOT AN EOM)
what nerve supplies the superior oblique
trochlear (IV)
what nerve supplies the lateral rectus
abducens (VI)
causes abduction of eye
what nerve supplies all other extrinsic eye muscles
occulomotor (III)
What does RADSIN stand for
Recti ADduct
Superiors INtort
What are the actions on the eye of the medial recuts
adduction
What are the actions on the eye of the lateral rectus
abduction
What are the actions on the eye of the superior rectus
- elevation
- adduction
- intorsion
What are the actions on the eye of the inferior rectus
- depression
- adduction
- extorison
What are the actions on the eye of the superior obliques
- introrsion
- depression
- abduction
What are the actions on the eye of the inferior obliques
- extorsion
- elevation
- abduction
what is strabismus
squint - misalignment of the eyes
what are the two types of squint
- esotropia (manifest convergent squint)
2. exotropia (manifest divergent squint)
what are the 2 functional consequences of squint
- amblyopia (lazy eye) - brain suppress image of one eye leading to poor vision in that eye (no pathology)
- diplopia (double vision) - usually occurs in squints occurring as a result of nerve palsies
what are the three intrinsic muscles of the eye
- ciliaris muscle (in ciliary body)
- constrictor pupillae (in iria at pupillary border)
- dilator pupillae (radially running muscle in iris)
what innervates the ciliary muscle
parasympathetic oculomotor (III) nerve
what innervates the constrictor pupillae
parasympathetic oculomotor (III) nerve
what innervates the dilator papillae
sympathetic plexus around blood vessels
what is the pupillary reaction to increased light
parasympathetic innervation = both pupils constrict
what is the pupillary reaction to decreased light
sympathetic innervation = both pupils dilate
what is the AFFERENT limb pathway of the light reflex
light falls on retina - impulses travel along optic nerve - optic chiasma - optic tract
fibres don’t go to the lentiform geniculate body - instead leave optic tract and go straight to midbrain (oculomotor III nucleus)
part of III nucleus is the Edinger-westphal nucleus for parasympathetic fibres -
what is the EFFERENT limb pathway of the light reflex
from EWN (part of III nucleus) - preganglionic parasympathetic pass through III into orbit
parasympathetic fibres for to and synapes in ciliary ganglion
post ganglionic fibres go through short ciliary nerves to constrictor pupillae
pupillary constriction of BOTH EYES
what are 2 examples of pupil abnormalities
- pupils may be different size - anisocoria e.g. corners syndrome
- pupils may look normal but react abnormally to light (abnormal light reflex)
what can cause absent/abnormal pupillary reflexes
- any abnormality of the afferent limb/ centre / efferent limb of the reflex
- diseases of the retina - detachment, degeneration, dystrophy
- diseases of the optic nerve - e.g. optic neuritis in MS
- diseases of the III cranial nerve (efferent limb)
what must you check for if there is a III nerve palsy due to a medical cause e.g. diabetes
medical cause = no damage to parasympathetic fibres
check pupillary reflex - if absent - suspect cerebral artery aneurysm = EMERGENCY
what is anisocoria that occurs in horners syndrome
damage to the sympathetic innervation of the pupil - causes pupil to be unable to dilate in dark conditions
what is the triad of eye symptoms in horners syndrome
anisocoria - pupils different size
ptosis - drooping of eyelid on affected side
anhidrosis - loss of sweating on the affected side
what can cause horners syndrome
any disruption along sympathetic chain innervation - e.g. pancoasts tumour of the lung
(thoracolumbar outflow, sympathetic chain, cervical ganglia, postganglionic sympathetic fibres travelling with blood vessels in head and neck)
