Vision 2 Flashcards
Visual field
Everything you see with one eye (including in the periphery)
How is the visual field tested?
- Confrontation test (outpatient screening)
- Automated perimetry
What should visual field testing not be confused with?
-Visual acuity testing
How are images of objects in your field of vision formed?
Upside down and inverted on your retina
Where do all fibres from the eye pass through?
Optic nerve to the optic chiasma
What happens at the optic chiasma?
The (medial) nasal fibres cross to the opposite side
What fibres does the optic tract contain?
- 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
Where do fibres from the optic tract synapse?
LGB of the thalamus
What happens after the optic tract synapses?
The optic radiation passes behind the internal capsule (retro-lentiform fibres) to reach the primary visual cortex in the occipital lobe (area 17)
What damage do you expect when the right optic nerve is damaged?
Blindness right eye
What damage do you expect when the optic chiasma is disrupted in the middle?
Bitemporal hemianopia
What damage do you expect if the right optic tract is damaged?
Contralateral homonymous hemanopia
What type of damage do you expect if the optic radiation is damaged?
Contralateral homonymous hemianopia
What do intrinsic ocular muscles do?
- Control pupil diameter
- Helps alter lens curvature to enables us to see near objects
What do the extrinsic ocular muscles do?
Move the eye
What are the 6 extra ocular muscles?
- Medial rectus
- Lateral rectus
- Superior rectus
- Inferior rectus
- Superior oblique
- Inferior oblique
Where do the recti muscles arise from?
The apex of the orbit from an annular fibrous ring
Where does the superior oblique muscle arise from?
The roof (lesser wing of sphenoid) of the orbit posteriorly
Where does the inferior oblique arise from?
The floor of the orbit anteriorly
What muscle runs to the superior eyelid?
Levator palpebrae superioris
Where do the recti muscles insert anteriorly?
Sclera
Where do the oblique muscles insert?
Posteriorly
Where does the LPS originate?
Roof of orbit
What muscles are supplied by the oculomotor nerve?
- Medial rectus
- Superior rectus
- Inferior rectus
- Inferior oblique
- Levator palpebrae superioris
What muscle is supplied by the trochlear nerve?
Superior oblique
What muscle is supplied by the abducent nerve?
Lateral rectus
What are the actions of the extra ocular muscles influenced by?
- The muscles are attached along the orbital axis and not the optical axis so they pull o the eyeball at an angle. This means a muscle has more than 1 action
- 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
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?
- Introsion
- Depression
- Abduction
What are the acts of the inferior oblique?
- Extorsion
- Elevation
- Abduction
Strabismus
- Squint
- Misalignment of the eyes
Esotropia
Manifests convergent squint
Exotopia
Manifests divergent squint
What are the functional consequences of squint?
- Amblyopia
- Diplopia
Amblyopia
- Lazy eye
- Brain suppresses 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 are the 3 intrinsic muscles of the eye?
- Ciliaris muscle
- Constrictor pupillae
- Dilator pupillae
Where is the ciliaris muscle found?
Ciliary body
Where is the constrictor pupillae muscle found?
In the iris at the pupillary border
Where is the dilator pupillae muscle found?
Radially running muscle in the iris
What innervates the ciliaris muscle?
Parasympathetic fibres via oculomotor nerve
What innervates the constrictor pupillae muscle?
Parasympathetic fibres via oculomotor nerve
What innervates the dilator pupillae muscle?
Sympathetic fibres from the plexus around the blood vessels
What does pathology of innervation of the intrinsic muscles lead to?
Pupillary abnormalities
What is the ciliaris muscle for?
Focussing on near objects
What is the pupillary response to increased illumination?
- Parasympathetic
- Both pupils constrict
What is the pupillary response to decreased illumination?
- Sympathetic
- Pupils dilate
How should the pupillary reflex be elicited?
- Start in a dimly lit room (pupils dilated)
- Pen torch in front of one eye then check for both pupils constricting (direct and consensual reflex)
- Swing light to other side and both pupils should remain constricted
Describe the afferent limb aspect of the pathway of light reflex.
- Light falls on the retina
- Impulses travel along the optic nerve, chiasma and tract
- Fibres destined to activate the pupillary reflex do not go to the LGB, Instead they leave the optic tract to go to the midbrain (IIIn nucleus)
- Part of the IIIn nucleus is the Edinger-Westphal nucleus for parasympathetic fibres.
- The pupillary reflex fibres go to the EWN of both sides
Describe the efferent limb of the pathway for light reflex.
- From EWN, preganglionic parasympathetic fibres pass through IIIn into orbit
- Parasympathetic fibres go to and synapse in ciliary ganglion
- Postganglionic fibres go through short ciliary nerves to constrictor pupillary
- Pupillary constriction of both sides
Abnormal light reflex
Pupils look normal but react abnormally to light
Anisocoria
Different sized pupils
Give 2 examples of when anisocoria may occur.
- Horner’s syndrome
- Injury
What may cause an 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)
Why should you check pupillary reflex if someone presents with IIIn palsy?
- In IIIn palsy due to a medical cause such as diabetes, there is usually no damage to parasympathetic fibres
- Therefore if the reflex is absent suspect a cerebral artery aneurysm and treat it as an emergency
Ptosis
Drooping of the eyelid
Anhidrosis
Loss of sweating on affected side
Miosis
Excessive constriction of the pupil
What region is sympathetic outflow?
Thoracolumbar
