Vision 2 Flashcards
How does visual acuity vary over the visual field?
Closer to the periphery the lower the visual acuity
How would we test someones visual field
Confrontation testing for outpatient screening
Automated Perimetry
Describe the visual pathway?
- > Right Eye
- > Right nasal and temporal fibres pass along optic nerve
- > At optic chiasma nasal fibres from each eye swap
- > Right temporal and left nasal fibres pass along right optic tract
- > Synapses at Lateral Geniculate Body (LGB)
- > All fibres pass through right optic radiation
- > Reach Right Primary Visual Cortex
How is the visual field divvied up between eyes?
Nasal fibres see the temporal field for that eye
Temporal fibres see the nasal field for that eye
What would right optic nerve damage cause?
Blindness in the right eye
What does damage to the middle of the optic chiasma cause?
Youll lose both your nasal fibres resulting in loss of the temporal part of both fields of view.
Bitemporal Hemianopia
What happens if theres damage to the right optic tract?
The left nasal and right temporal fibres are damaged
Resulting in loss of the entire left visual field,
Contralateral Homonymous Hemianopia
What happens if theres damage to the right optic radiation?
Contralateral Homonymous Hemianopia
Contralateral (left field of vision)
Homonymous (same on both sides)
Hemianopia (loss of half the field)
So you’d lose left field of vision on both eyes if you damaeg the right optic radiation
Whats the function of the eyes intrinsic muscles and their nerve supply?
They control pupil diameter & lens curvature
Ciliaris & constricter pupillae get parasympathetic innervation from Cr N III.
Dilator Pupillae gets sympathetic innervation
Whats the function of extrinsic muscles of the eye and their innervation?
Also known as extraocular muscles.
They move the eye
Most are supplied by ophthalmic branch of the trigeminal nerve (Cr N V1).
The Sup oblique is supplied by the trochlear nerve (IV), because it has a trochlea
The main abducting muscle (Lateral Rectus) is supplied by the VI nerve (Abducens)
List the extrinsic eye muscles?
4 straight (recti):
- Medial rectus
- Lateral “
- Superior “
- Inferior “
2 Obliques:
- Superior Oblique
- Inferior “
From where do the recti muscles arise and insert?
They all arise from the annular fibrous ring at the apex of the orbit and insert onto the sclera anteriorly
Describe the path of the sup oblique muscle
Sup Oblique arises from roof of the orbit posteriorly (lesser wing of sphenoid).
It is slung to the superomedial front of the orbit and crosses by the superior rectus, inserting on the sclera lateral to the sup rectus
Describe the path of the inferior oblique
Arises from the maxillary bone and crosses under the eye to insert onto the lateral, inferior, posterior surface of the sclera.
What muscle elevates the eyelid?
The Levator Palpebrae Superioris
It runs from the roof of the orbit to the upper eyelid, basically on top of the sup rectus
There are two important things to remember when working out how muscles move the eye
1) That the orbital axis and optical axis are not in line. The muscles are in the orbital axis which points somewhat lateral whereas the optical is straight forward.
2) The oblique muscles attach to the posterior part of the eye so e.g. when the inf oblique contracts it will pull the posterior part down and ant part up.
Define the eye movements
Elevation
Depression
Abduction - Away from midline
Adduction - Towards midline
Intorsion - Top of eyeball rotates towards midline
Extorsion - Top of eyeball rotates away from midline
How do we remember the movements of the extraocular muscles?
RADSIN
Recti ADductors, Superiors Intortors
This means all the recti adduct (apart from the obvious lateral rectus which abducts)
And all the superiors intort
The opposite is also true:
- All the obliques abduct
- All the inferiors extort
This just leaves elevation and depression:
- IR depresses while SR elevates
- SO depresses while IO elevates
How would we test each of the recti muscles?
Lateral and medial recti are tested by abduction/adduction.
Sup/inf rectus elevate/depress when the eye is abducted.
Sup/Inf Obliques depress/elevate when the eye is adducted
Define Strabismus and its types
A squint, essentially misalignment of the eyes.
Esotropia - Manifest Convergent Squint
Exotropia - Manifest Divergent squint
A strabismus can have functional consequences, what are these?
Amblyopia (lazy eye)
Diplopia (double Vision)
How does Amblyopia occur and how do we treat it?
A lazy eye occurs when the brain suppresses the image of one eye
This causes poor vision in that eye without any pathology.
Its correctable when young with an eye patch to stimulate the lazy eye
How does diplopia arise from squint?
Strabismus occuring due to nerve palsy can lead to double vision.
What are the intrinsic eye muscles
- Ciliaris Muscle in the ciliary body
- Constrictor Pupillae in the iris at the pupillary border
- Dilator Pupillae, radially running in the iris
Disorders of these muscles or their innervation lead to pupillary abnormalities
What kind of innervation causes the pupils to dilate/constrict
Decreased light -> Sympathetic stimulation -> Pupillary dilation
And vice versa
How do you test the pupillary reflex?
Dimly lit room so pupils are dilated
Move the pen torch in front of one eye checking for direct and consensual constriction of the pupils.
Then swing the torch to the other eye, both pupils should remain constricted
Describe the afferent nerve path of the pupillary reflex
Optic Nerve -> Optic Chiasma -> Optic tract
Then leaves optic tract to enter midbrain, specifically the Cr III nucleus.
Within in the Cr III nucleus is the Edinger-Westphal Nucleus (EWN) which contains parasympathetic fibres.
That’s where the pupillary reflex passes.
Describe the efferent nerve path of the pupillary reflex?
EWN aka accessory oculomotor nucleus recieves fibres from the optic tract
- -> Pre-ganglionic parasympathetic fibres in Oculomotor nerve
- -> Synapses in Ciliary Ganglion
- -> Post-ganglionic parasympathetic fibres in short ciliary nerves
- -> Constrictor Pupillae
Summary of pupillary reflex path:
Optic Nerve -> Optic Chiasma -> Optic Tract -> EWN (within Cr III nuclues within midbrain)
EWN -> Pre-ganglionic parasympathetic fibres in Oculomotor nerve -> Ciliary ganglion -> Post-ganglionic sympathetic fibres in short ciliary nerves -> Constrictor Pupillae
List some pupil abnormalities?
Aniscoria - Pupils of different sizes
Abnormal Light Reflex
What could cause Anisocoria?
Pupils of different sizes is most commonly caused by Horner’s Syndrome or Injury
How does Horner’s Syndrome occur?
Damage to the sympathetic innervation of the eye at any stage:
- Outflow from spine
- Symp Chain
- Cervical Ganglia
- Postganglionic Symp Fibres
E.g. a pancoast tumour
What are the symptoms of Horner’s syndrome?
- Ptosis (drooping or falling of the upper eyelid)
- Miosis (Excess pupil constriction)
- Anhidrosis (Inability to sweat normally)
All on one side of the face
Define the abnormal light reflex?
The pupils appear normal at rest but react abnormally to light
What could cause Abnormal Light Reflex?
Diseases of the optic nerve e.g. neuritis (often found in MS)
Diseases of the oculomotor nerve
Diseases of the retina
e.g. Detachment, Degeneration or Dystrophy
