Vision 2 Flashcards
What are the two types of ocular muscles?
Intrinsic muscles:
- Control pupil diameter
- helps alter lens curvature
- Enable us to see near objects
Extrinsic muscles:
- Also called extra ocular muscles or EOMs)
- Move the eye
What are the 4 straight and 2 oblique extrinsic ocular muscles that move the eye?
Straight muscles called recti:
- Medial rectus
- Lateral rectus
- Inferior rectus
- Superior rectus
Oblique muscles:
- Superior Oblique
- Inferior Oblique
Where do the extrinsic muscles of the eye arise from in the orbit?
The recti muscles arise from the apex of the orbit from an annular fibrous ring.
The superior oblique muscles arise from the roof of the orbit posteriorly
The inferior oblique muscles arise from the floor of the orbit anteriorly
What muscle closes the eyelid?
Levator Palpebrae Superioris
It lies just superiorly to the superior rectus muscle
Where do the extrinsic ocular muscles attach to the eye?
The recti muscles insert onto the sclera anteriorly
Obliques insert posteriorly
What is the origin and insertion of the Levator palpebrae superioris?
Origin: roof of orbit
Insertion: upper eyelid
What is the origin and insertion of all the recti muscles of the eye?
Origin: tendinous ring
Insertion: sclera posteriorly
What is the origin and insertion of the superior oblique muscle?
Origin: lesser wing of sphenoid
Insertion: Sclera posteriorly
What is the origin and insertion of the inferior oblique muscle?
Origin: medial part of orbit floor
Insertion: sclera posteriorly
Is the obicularis oculi an EOM?
No
Muscle of facial expression
What is the nerve supply to the extrinsic ocular muscles?
Trochlear (IV) nerve supplies muscle with trochlea (SO)
-Only muscle it supplies in the whole body
Abducent (VI) nerve supplies muscle which abducts (LR)
Everything else
-Oculomotor (III) nerve
The action of individual EOMs are influenced by 2 factors. What are they?
The muscles are attached along the orbital axis and not the optical axis, so they pull on the eyeball at an angle.
This is why the superior and inferior recti have more than 1 function.
The oblique muscles are attached to the posterior part of the sclera, so they pull the posterior part of the eyeball up/down and the anterior part moves in the OPPOSITE direction
How do you test the actions of EOMs?
The obliques elevate/depress when the eye is adducted.
The recti (SR and IR) elevate/depress when the eye is abducted
What is a sign of right third nerve palsy?
Drooping eyelid
Eye can move only laterally (and slightly down)
What is a sign of left fourth nerve palsy?
Eye moving up when adducted
What is a sign of Abducent (6th) nerve palsy?
Eye being adducted
Eye not able to abduct
What is Strabismus?
Squint (misalignment of the eyes)
What are the two types of Strabismus?
Esotropia (manifest convergent squint)
Exotropia (manifest divergent squint)
What are the functional consequences of strabismus?
Amblyopia (lazy eye)
- Where brain surpasses the image of one eye leading to poor vision in that eye without any pathology
- Correctable in early years using eye patches to stimulate the “lazy” eye to work
Diplopia (double vision)
-Usually occurs in squints occurring as a result of nerve palsies
What is a visual field?
Everything you see with one eye (including in the periphery) is your visual field.
Images of objects in your field of vision is formed in upside down and inverted on your retina
Describe the visual pathway in depth up to the formation of the optic tract
All fibres from the eye pass through the optic nerve to the optic chiasma.
At the optic chiasma the (medial) nasal fibres cross to the opposite side.
So the optic tract contains fibres from the (lateral) temporal half of the ipsilateral eye and the crossed over nasal fibres from the contralateral eye.
This corresponds to ALL fibres from the opposite half of the visual field.
Describe the visual pathway in depth from the formation of the optic tract
Fibres from the optic tract synapse at the lateral geniculate body of the thalamus.
From here the optic radiation passes behind the Internal Capsule (retro-lentiform fibres) to reach the Primary Visual Cortex in the Occipital lobe (Area 17)
Thus the right visual cortex sees the left half of the visual field and vice versa.
Describe the visual pathway very basically
Image -> optic nerve -> optic chiasma -> optic tract -> lateral geniculate body of thalamus -> optic radiation -> visual cortex
What symptom/sign would someone have if their right optic nerve was damaged?
Blindness in one eye
