Lecture 10 Eye Muscles Flashcards
What do the intrinsic ocular muscles control
control pupil diameter & helps alter lens curvature to enable us to see near objects
What do the extrinsic ocular muscles do (extra ocular)
Move the eye
How many extra ocular muscles are there
6
Name the extra ocular muscles
Superior rectus Inferior rectus Lateral rectus Medial rectus Superior oblique Inferior oblique
Where do the recti muscles arise from
Arise from 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 the orbit anteriorly
Where does the elevator palpebral superiors lie and what is its purpose
Just above the superior rectus and elevates the eyelid
Where do the rectify muscles insert into the sclera
Anterioirly
Where do the oblique muscles insert into the sclera
Posteriorly
What are the muscles in the face that close the eyelids
Orbicularis oculi
What are the 2 parts of the orbicularis oculi
orbital and palpebral sections
Where does the orbicularis oculi arise from
It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short fibrous band, the medial palpebral ligament
Define uniocular
Movement of one eye
Define binocular
Movement of two eyes
Define intorsion
When the top of the eyeball rotates towards the nose
Define Extorsion
When the top of the eyeball rotates away from the nose
What is the action of the medial rectus
Adduction
What is the action of the lateral rectus
Abduction
What are the actions of the superior rectus
Elevation
Adduction
Intorsion
What are the actions of the inferior rectus
Depression
Adduction
Extorsion
What are the actions of the superior oblique
Intorsion
Depression
Abduction
What are the actions of the inferior oblique
Extorsion
Elevation
Abduction
Why do extra ocular muscles except for the medial and lateral rectus have more than one action
due to the angle they make with the optical axis of the eye while inserting into the eyeball.
Why do the muscles pull the eyeball at an angle
The muscles are attached to the orbital axis not the optical axis
What muscle is the only elevator of the abducted eye
Superior rectus
What is Strabismus
Squint (misalignment of the eyes)
What are the 2 types of Strabismus
- Esotropia (manifest convergent squint)
* Exotropia (manifest divergent squint)
What are the functional consequences of a squint
Amblyopia (brain surpasses the image of one eye)
Diplopia (nerve palsies)
Name the intrinsic muscles in the eye
Ciliaris
Sphincter Pupillae
Dilator Pupillae
What innervation of the intrinsic muscles
Ciliaris- parasympathetic (oculomotor, ciliary ggl.)
Sphincter- parasympathetic (oculomotor, ciliary ggl.)
Dilator- sympathetic. (T1, sup, cervical ggl.)
What happens to the pupils in increased illumination
Both pupils constrict
What happens to pupils in decreased illumination
Pupils dilate
Fibres destined to activate the pupillary reflex go where after the optic tract (afferent pathway)
Do not go to the LGB instead leave optic tract to go the midbrain (where IIIn nucleus is situated) Edinger-Westphal nucleus
Describe the efferent pathway of the light reflex
From EWN in IIIn nucleus, preganglionic parasympathetic pass through IIIn into orbit.
Parasympathetic fibres go to & synapse in ciliary ganglion.
Postganglionic fibres go through short ciliary nerves to constrictor pupillae
What is the LGB
Lateral Geniculate Nucleus
A relay centre in the thalamus for the visual pathway.
Receives major sensory input from the retina
What condition can cause pupil abnormalities
Horner’s Syndrome- pupils look different sizes anisocoria
What are some common causes of absent/abnormal pupillary reflex
- Any abnormality of the afferent limb/ centre / efferent limb of the reflex
- Diseases of the retina – detachment/ degenerations or dystrophies
- Diseases of the optic nerve – such as in optic neuritis (frequently seen in MS)
- Diseases of the III cranial nerve (efferent limb)
What is the afferent limb of the pupillary reflex made of
Retina, opic nerve, IIIn nucleus (EWN)
What is the efferent limb of the pupillary reflex made of
IIIn nucleus (EWN), ciliary ganglion, ciliary sphincter muscle
What innervation is damaged in Horner’s syndrome and what is the consequence
Sympathetic innervation
Affected pupil cannot dilate so is constricted
Horner’s syndrome can occur due to the disruption of
- Thoracolumbar outflow of the sympathetic
- Sympathetic chain and cervical ganglia
- Head and neck – postganglionic sympathetic fibres travel along with blood vessels
- E.g. Pancoast tumour of the lungs
