Muscles of the Eye Flashcards
What are the different categories of the occular muscles?
Intrinsic muscles
Extrinsic muscles
What do the intrinsic muscles do?
Controls the pupil diameter and helps lens curvature to enable us to see near objects
What do the extrinsic muscles do?
Move the eye
What are the 6 extrinsic muscles?
4 straight muscles called recti:
medial rectus
lateral rectus
inferior rectus
superior rectus
2 oblique msucles:
superior oblique
inferior oblique
Where do the recti extrinsic muscles arise from?
Apex of the orbit from an annular fibrous ring
Where does the superior oblique muscle arise from?
Roof of the orbit posteriorly
Where does the inferior oblique muscle arise from?
Floor of orbit anteriorly
What muscle runs to the upper eyelid and elevates it?
Levator palpebrae superioris
Where does the levator palpebrae superioris lie?
Above the superior rectus muscle
What is the origin of the levator palpebrae superioris?
Roof of orbit
What is the insertion of the levator palpebrae superioris?
Upper eyelid
What is the origin of all recti muscles?
Tendinous ring
What is the insertion of all recti muscles?
Sclera anteriorly
What is the origin of the superior oblique muscle?
Lesser wing of sphenoid
What is the insertion of the superior oblique muscle?
Sclera posteriorly
What is the origin of the inferior oblique muscle?
Medial part of orbit floor
What is the insertion of the inferior oblique muscle?
Sclera posteriorly
What are factors that affect the way muscles pull the eye?
Axis of orbit vs eyeball (muscles are attached along orbital axis not optical axis, so they pull at an angle and each muscle has more than one action)
Where the muscles attaches to sclera in relation to the equator of the eye (oblique muscles are attached to posterior part fo they pull posterior part up/down and anterior part moves in the opposite direction)
What are uniocular eye movements?
What are binocular eye movements?
What is intorsion?
When the top of the eyeball rotates towards the nose
What is extorsion?
When the top of the eyeball rotates away from the nose
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the medial rectus?
Primary - adduction
Secondary - none
Tertiary - none
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the lateral rectus?
Primary - abduction
Secondary - none
Tertiary - none
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the superior rectus?
Primary - elevation
Secondary - adduction
Tertiary - intorsion
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the inferior rectus?
Primary - depressoin
Secondary - adduction
Tertiary - extorsion
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the superior oblique?
Primary - intorsion
Secondary - depression
Tertiary - abduction
Each muscle has a primary, maybe secondary, and maybe tertiary action. What are the action(s) of the inferior oblique?
Primary - extorsion
Secondary - elevation
Tertiary - abduction
Why do muscles have more than one action?
They are attached along the orbital axis not the optical axis
What is the only elevator of the abducted eye?
Superior rectus
In the abducted position what muscle elevates/depresses the eye?
Superior and inferior obliques
In the adducted position, what muscles elevate/depress the eye?
Superior and inferior recti
What is the clinical condition where the muscles of the eye do not work properly?
Strabismus (squint)
What is a strabismus?
Misalignment of the eyes
What are the 2 kinds of strabismus?
Esotropia (manifest convergent squint)
Exotropia (manifest divergent squint)
What are the functional consequences of a strabismus?
Ambylopia (lazy eye)
Diplopia (double vision)
What is ambylopia?
The brain suppresses the image of one eye leading to poor vision in that eye without any pathology (lazy eye)
What is diplopia?
Double vision, usually occurs in quints occuring as a result of nerve palsies
What is the medical term for a lazy eye?
Amblyopia
What are the 3 intrinsic muscles of the eye?
Cilaris muscle
Constrictor pupullae
Dilator pupillae
What is the ciliaris muscle for?
Focussing on near objects
What is the ciliaris muscle innervated by?
Parasympathetic nervous system (CN III)
What is the constrictor pupillae innervated by?
Parasympathetic nervous system (CN III)
Where is the ciliaris muscle found?
In ciliary body
Where is the constrictor pupillae muscle found?
In iris at pupillary border
What shape of muscle is the constrictor pupillae?
Circular muscle
Where is the dilator pupillae found?
Radially running muscle in iris
What is the dilator pupillae innervated by?
Sympathetic nervous system fom plexus around blood vessels
What shape is the dilator pupillae muscle?
Radially running longitudinal muscle
How does increased illumination impact the pupil?
Activates parasympathetic nervous system that leads to both pupils constricting
How does decreased illumination impact the pupil?
Activates the sympathetic nervous system that leads to both pupils dilating
Explain the process of eliciting the pupillary reflex?
1) Start in a dimly lit room (pupils dilated)
2) Pen torch in front of one eye checking both pupils constricting (direct and consensual reflex)
3) Swing the light to the other side, both pupils should remain constricted
What are the 2 pathways for light reflex?
Afferent limb
Efferent limb
Explain the process of the afferent limb pathway for light reflex?
1) Light falls on the retina causing impulses to travel along the optic nerve -> optic chiasma -> optic tract
2) Fibres destined to activate the pupillar reflex do not go to the LGB, instead they leave the optic tract and go to the midbrain where the IIIn nucleus is situated)
3) Part of the IIIn (CN III) nucleus is the Edinger-Westphal nucleus (EWN) for parasympathetic fibres, the pupillary reflec fibres go to EWN of both sides
What does EWN stand for?
Edinger-Westphal nucleus
Explain the process of the efferent limb for light reflex?
1) From EWN (part of IIIn nucleus)
2) Preganglionic parasympahetic pass through IIIn into orbit
3) Parasympathetic fibres go to and synapse in ciliary ganglion
4) Postganglionic fibres go through short ciliary nerves to constrictor papillae
5) Pupillary constriction of both sides
What is the medical term for pupils being different sizes?
Anisocoria
What is an example of an abnormality where the pupils are different sizes?
Horner’s syndrome
What is Horner syndrome?
Rare disorder characterised by constricted pupil (miosis), drooping of the upper eyelid (ptosis), absence of sweating of the face (anhidrosis) and sinking of the eyeball into the bony cavity that protects the eye (enophthalmos)
How can pupils be abnormal but look normal?
May look normal but react to light abnormally (abnormal light reflex)
What are some examples of causes of absent/abnormal pupillary reflex?
Any abnormality of afferent limb/centre/efferent limb of the reflex
Diseases of the retina (detachment, degernation, dystrophies)
Diseases of the optic nerve (such as optic neuritis)
Diseases of CN III (efferent limb problem)
What is an example of a medical cause that can cause IIIn palsy?
Diabetes
What is the medical term for drooping of the eyelids?
Ptosis
What is the medical term for loss of sweating?
Anhidrosis
In Horner’s syndrome, which pupil is constricted?
Pupil of the affected eye
Explain the sympathetic innervaiton of the eye?
Thoracolumbar outflow of the sympathetic
Sympathetic cain and cervical ganglia
In head and neck postganglionic fibres travel along with blood vessels
What is an example of something that can cause Horner’s syndrome?
A disruption at any point of the sympathetic pathway, an example being Pancoast’s tumour of the lungs
