Vision 2 Flashcards
How does visual acuity vary over the visual field? [1]
Closer to the periphery the lower the visual acuity
How would we test someones visual field [2]
Confrontation testing for outpatient screening
Automated Perimetry
Describe the visual pathway of the right eye? [7]
- > Right Eye
- > Right nasal and temporal fibres pass along optic nerve
- > At optic chiasma, nasal fibres from each eye decussate
- > 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? [4]
Nasal fibres process the temporal field [2]
Temporal fibres process the nasal field [2]
What would right optic nerve damage cause? [1]
Blindness in the right eye
What does damage to the middle of the optic chiasma cause? [3]
Youll lose both your nasal retinal fibres [1] resulting in loss of the temporal part of both fields of view [1]
Bitemporal Hemianopia [1]
What happens if theres damage to the right optic tract? [4]
What happens if theres damage to the right optic radiation? [1]
The left nasal [1] and right temporal fibres [1] are damaged
Resulting in loss of the entire left visual field [1]
Contralateral Homonymous Hemianopia [1]
Damage to right optic radiation would result in contralateral homonymous hemianopia
Explain the term Contralateral Homonymous Hemianopia [3]
Contralateral (left field of vision)
Homonymous (same on both sides)
Hemianopia (loss of half the field)
Whats the function [2] of the eyes intrinsic muscles and their nerve supply? [5]
They control pupil diameter & lens curvature
Ciliaris & constricter pupillae get parasympathetic innervation from Cr N III [3]
Dilator Pupillae gets sympathetic innervation [2]
EOM - innervation [3]
Most are supplied by ophthalmic branch of the trigeminal nerve (Cr N V).
The Sup oblique is supplied by the trochlear nerve (IV),
The main abducting muscle (Lateral Rectus) is supplied by the VI nerve (Abducens)
List the extrinsic eye muscles [6]
4 straight (recti):
- Medial rectus
- Lateral “
- Superior “
- Inferior “
2 Obliques:
- Superior Oblique
- Inferior “
From where do the recti muscles arise and insert? [3]
They all arise from the annular fibrous ring [1] at the apex of the orbit [1] and insert onto the sclera anteriorly [1]
What muscle elevates the eyelid? [2]
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 [6]
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
Define Strabismus [2] and its types [2]
A squint, essentially misalignment of the eyes [2]
Esotropia - Convergent Squint
Exotropia - Divergent squint
A strabismus can have functional consequences, what are these? [2]
How is strabismus diagnosed [4]
Ambylopia (lazy eye)
Diplopia (double Vision)
- Corneal reflection: reflection from bright light [1] falls centrally and symmetrically on each cornea if no squint [1] and asymmetrically if there is a squint
- Cover test: movement of uncovered eye [1] to take up fixation [1] as other eye is covered demonstrates manifest squint
Strabismus arises from amblyopia. What is amblyopia?
Management - describe 3 modes of treatment [6]
A lazy eye occurs when the brain suppresses the image of one eye (visual deprivation [1])
This causes poor vision in that eye
Management
Start treatment as soon as squint is noticed, earlier the better
- Optical - assess refractive state after cylcopenatolate drops (cyclopedia), correct refractive errors
- Orthoptic exercises
- Occlusion: patching good eye encourage use of one which squints
- Operation - resection/recession of rectus muscles, botulinum toxin
How does diplopia arise from squint? [1]
Strabismus occuring due to nerve palsy can lead to double vision.
What kind of innervation causes the pupils to dilate/constrict [3]
Decreased light -> Sympathetic stimulation -> Pupillary dilation
And vice versa
What pupillary tests can you do in a clinical setting? [2]
Direct and consensual pupillary reflex
Describe the afferent nerve path of the pupillary reflex [3]
Optic Nerve -> Optic Chiasma -> Optic tract [1]
Then leaves optic tract to enter midbrain, specifically the Cr III nucleus. [1]
Within in the Cr III nucleus is the Edinger-Westphal Nucleus (EWN) which contains parasympathetic fibres. [1]
That’s where the pupillary reflex passes.
Describe the efferent nerve path of the pupillary reflex? [5]
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? [2]
Aniscoria - Pupils of different sizes
Abnormal Light Reflex
What could cause Anisocoria? [2]
Horner’s Syndrome
Injury
How does Horner’s Syndrome occur? [5]
Give one cause for Horner’s syndrome
Damage to the sympathetic innervation of the eye at any stage: [1]
- Outflow from spine
- Symp Chain
- Cervical Ganglia
- Postganglionic Symp Fibres
Pancoast tumour
What are the symptoms of Horner’s syndrome? [4]
- 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? [2]
The pupils appear normal at rest but react abnormally to light
Describe the light reflex you would expect in:
Lesion on left optic nerve [1]
No pupillary response bilaterally
Describe the light reflex you would expect in:
Damage to optic chiasm [1]
Light reflex still normal
Describe the light reflex you would expect in:
Lesion on left occulomotor nerve [2]
Direct reflex absent
Consensual reflex present
Describe the light reflex you would expect in:
Lesion on right oculomotor nerve [2]
Direct reflex present
Consensual reflex absent
Cover test in squints [4]
Convergent/divergent squint
Manifest squint: present when eyes open and being used
Latent squint: present only when eyes have been closed; affected eye moves after cover has been removed from the affected eye
Eccentric fixation: foveal vision is so poor that deviated eye doesn’t move to take up fixation
