Vision 2 Flashcards
What are the two types of ocular muscle?
Intrinsic and extrinsic
What are the functions of intrinsic ocular muscles?
Controlling pupil diameter, altering lens curvature to enable short range focus
What is the function of extrinsic ocular muscles?
Moving the eye
What are the four straight extrinsic ocular muscles?
Medial, lateral, superior and inferior rectus
What are the two oblique extrinsic muscles?
Superior and inferior oblique
Where do the recti muscles arise from?
The apex of the orbit from an annular fibrous ring called the trochlea
Where does the superior oblique muscle arise from?
The roof of the orbit posteriorly
Where does the inferior oblique arise from?
The floor of the orbit anteriorly
What muscle runs above the SR elevating the eyelid?
Levator palpebrae superioris
What nerve innervates the superior oblique?
Tochlear
What nerve supply the lateral rectus?
Abducent
What nerve supples the majority of the muscles of the eye?
Oculomotor
What is the action of the superior rectus?
when the eye is abducted the SR causes elevation
When the eye is adducted the SR causes intorsion
What is the action of the inferior rectus?
When the eye is abducted the IR causes depression
When the eye is adducted the IR causes extortion
What is the action of the superior oblique?
When the eye is adducted the SO causes depression
Overall it causes intorsion, depression, abduction
What is the action of the inferior oblique?
When the eye is adducted the IO causes elevation
Overall, the IO causes extorsion, elevation, abduction
What should looked for in suspected right third nerve palsy?
Drooping eyelid, eye only has full movement laterally
What should be looked for in suspected left fourth nerve palsy?
Eye moving up when adducted
What should be looked for in suspected abucent nerve palsy?
Eye being adducted, eye not able to adduct
What is strabismus?
Squint
What are the two kinds of strabismus?
Esotropia - convergent
Exotropia - divergent
What is amblyopia?
Lazy eye - where the brain suppress the image of one eye leading to poor vision in that eye without any pathology
What is diplopia?
Double vision - usually occurs in squints occurring as a result of nerve palsies
Describe the visual field
Everything that can be seen with one eye, including the periphery
In what orientation do images form on the retina?
Upside down, they are inverted in the retina
Describe the optic pathway
All fibres from the eye pass through the optic nerve tot he optic chiasm
At the chasm the medial nasal fibres cross to the opposite side
So the optic tract contents fibres from the lateral/temporal half of the ipsilateral eye and the crossed-over fibres from the contralateral side
This corresponds to all fibres from the opposite side of the visual field
Fibres from the optic tract synapse at the LGB (lateral geniculate body) of the thalamus
From here the optic radiation passes behind the internal capsule (retro-lentiform) to reach the Primary Visual Cortex area in the Occipital lobe
i.e. the right visual cortex sees the let half of the visual field and vice versa
What would be the effect of a lesion to the right optic nerve?
Blindness in the right eye
What would be the effect of the optic chasm being disrupted in the middle?
Bitemporal hemianopia
What would the effect be of a right optic tract lesion?
Contralateral homonymous hemianopia
What would the effect of damage to the optic radiation?
Contralateral homonymous hemianopia
What are the intrinsic muscles of the eye?
Ciliaris
Constrictor pupillae - circular
Dilator pupillae - radial
Does increased illumination lead to a parasympathetic or sympathetic response?
Parasympathetic - pupils contract
Does decreased illumination lead to a parasympathetic or sympathetic response?
Sympathetic - pupils dilate
Do the fibres relating to pupillary reflex activation use the same pathway as the normal fibres?
No, they do not go to the LGB but instead leave the optic tract to go to the midbrain where the IIIn nucleus is situated. Part of it is the EWN for parasympathetic fibres. The fibres go to both sides of the EWN
What is anisocoria?
Pupils of differing size
Describe the efferent pathway of the light reflex
From the EWN nucleus, preganglionic fibres pass through IIIn into the orbit. Parasympathetic fibres go to synapse at the ciliary ganglion. Postganglionic fibres go through short ciliary nerves to constrictor pupilae = pupillary constriction on both sides
What is Horner’s syndrome?
Anisocoria due to damage to the sympathetic innervation to the pupil - therefore affected pupil constricted
