Eye Muscles Flashcards
Name the two main types of strabismus (squint)
- Esotropia (manifest convergent squint)
- Exotropia (manifest divergent squint)
Name the functional consequences of a squint
- Amblyopia (lazy eye): where the brain suppresses the image of one eye leading to poor vision in that eye
- Diplopia (double vision): usually occurs as a result of nerve palsies
What does anisocoria mean?
Pupils of different sizes
Name some common causes of absent/abnormal pupillary reflexes
- Diseases of the retina: detachment, degenerations or dystrophies
- Diseases of the optic nerve e.g. optic neuritis
- Diseases of CrN III (not medical causes such as diabetes)
Describe the features of Horner’s syndrome
- Anisocoria due to damage to the sympathetic innervation to the pupils
- Ptosis (drooping of the eyelid)
- Miosis (constriction of the pupil) on the affected side
- Anhidrosis
What is the function of the intrinsic ocular muscles?
Controls pupil diameter and helps alter the lens curvature (allows us to see near objects)
What is the function of the extrinsic ocular muscles?
They move the eye
Name the six extrinsic ocular muscles
- Medial rectus
- Lateral rectus
- Inferior rectus
- Superior rectus
- Superior oblique
- Inferior oblique
Where do the recti muscles arise from?
An annular fibrous ring at the apex of the orbit
Where does the superior oblique muscle arise from?
The roof of the orbit posteriorly
Where does the inferior oblique muscle arise from?
The roof of the orbit anteriorly
Which muscle elevates the eyelid?
levetator palpebrae superioris
Which muscle is supplied by the trochlear nerve?
Superior oblique
Which muscle is supplied by the abducent nerve?
Lateral rectus
Which nerve supplies most of the extrinsic ocular muscles?
Oculomotor nerve
What is the action of the medial rectus muscle?
Adduction
What is the action of the lateral rectus muscle?
Abduction
What are the functions of the superior rectus muscle?
- Elevation
- Adduction
- Intorsion
What are the functions of the inferior rectus muscle?
- Depression
- Adduction
- Extorsion
What are the functions of the superior oblique muscle?
- Intorsion
- Depression
- Abduction
What are the functions of the inferior oblique muscle?
- Extorsion
- Elevation
- Abduction
Name the three intrinsic eye muscles
- Ciliaris muscle
- Constrictor pupillae
- DIlator pupillae
How are the intrinsic eye muscles innervated?
- Ciliaris and constrictor pupillae are innervated by parasympathetic fibres from CrN III
- Dilator pupillae is innervated by sympathetic fibres
Describe the pathway of the light reflex
- Light falls on the retina and travels through the optic nerve and chiasma to the optic tract
- The fibres for the pupillary reflex go to the midbrain to the CrN III nucleus where the Edringer-Westphal nucleus (parasympathetic) is located
- Preganglionic parasympathetic fibres pass through CrN III into the orbit
- These fibres synapse in the ciliary ganglion
- Postganglionic fibres go through the short ciliary nerves to constrictor pupillae
- Pupillary constriction on both sides
