Part 2

• What does the central retinal artery supply?

  Inner retinal layers
• What does the posterior ciliary artery supply?

  Supplies the optic nerve & feeds into the choroid which supplied the RPE & photoreceptors & the optice nerve
• What are the possible optic nerve problems?

  Inflammation (optic neuritis)

  Glaucoma

  Ischaemia

  Compression

  Papilloedema
• What can optic nerve problems cause?

  Reduced visual acuity

  Altered colour vision

  Visual field defects

  Relative Afferent Pupil Defects
• What is optic neuritis?

  Inflammation of optic nerve

  Can result in variable visual loss, but usually recovers within a few months

  50% due to MS, can be post-viral
• What is shown in these images?

  Optic neuritis

  
• What is glaucoma?

  Progressive optic neuropathy

  Causes loss of the nerve fibre layer -> cupped optic disc appearance & corresponding visual field defects

  Commonly associated with raised intra-ocular pressure
• What is shown in the image?

  Glaucoma

  
• What is anterior ischaemic optic neuropathy?

  Loss of vision due to problem with posterior ciliary artery

  Get pale optic disc, but normal looking retina

  Most commonly due to microvascular occlusion related to diabetes, HTN & atherosclerotic disease, can be due to inflammatory causes (Giant Cell Arteritis)
• What can cause optic nerve compression?

  Inflammatory conditions (thyroid eye disease)

  Infection (orbital cellulitis)

  Haemorrhage

  Tumours
• What is orbital cellulitis?

  Bacterial infection of skin, fat & muscles around eye
• NOTE: Not all disc swelling is papilloedema!
• What is papilloedema?

  Swollen optic disc with raised intracranial pressure

  Usually bilateral & vision is minimally disturbed

  Increased blind spot & increased peripheral field loss may occur
• Fill in the blanks

  A) Retina

  B) Optic nerve

  C) Optic chiasm

  D) Optic tract

  E) Lateral geniculate nucleus

  F) Optic radiation

  G) Visual cortex

  
• Fill in the blanks

  A) Superior rectus

  B) Superior oblique

  C) Lateral rectus

  D) Inferior rectus

  E) Inferior oblique

  F) Medial rectus

  
• How does raised intra-cranial pressure papilloedema?

  Optic nerve is surrounded by a sheath containing CSF, continuous with subarachnoid space

  Increased intra-cranial pressure -> pressure on optic nerve -> reducing axoplasmic flow at optic nerve head -> oedema -> venous stasis & haemorrhages
• Pupil constriction

  Parasympathetic NS -> stimulates contraction of circular muscles (sphincter pupillae)

  Light enters eye -> stimulates retina -> signals travel via optic nerve & synapse with the pre-tectal nucleus -> synapses with Edinger-Westphal (oculomotor) nucleus -> gives rise to bilateral oculomotor outputs to ciliary ganglion -> short ciliary nerve innervates the sphincter pupillae (circular muscle) -> pupil constriction 
• What is the accommodation reflex?

  Visual response to focus on nearby objects
• What does the accommodation reflex involve?

  Pupil constriction

  Accommodation of lens (change in lens shape) -> via short ciliary nerve

  Convergence -> via CN III, media rectus muscle action
• What are the potential causes of abnormal pupils?

  Marcus Gunn (RAPD)

  Holmes-Adie

  Argyll-Robertson

  Horner's

  3rd nerve palsy

  Pharmacological
• Pupil dilation

  Sympathetic NS -> stimulates contraction of radial muscles (dilator pupillae) 

  Begins in hypothalamus & descends through midbrain -> synapses in spinal cord (C8-T2) -> preganglionic sympathetic neuron exits spinal cord (through ventral roots) -> projects to superior cervical ganglion & synapses -> long ciliary nerve projects to dilator pupillae (radial muscle) -> pupil dilation 
• What is Marcus Gunn pupil (RAPD)?

  Equally sized pupils

  Light -> dilates to direct light & constricts to indirect in swinging light test

  Accommodation -> same as light

  Optic nerve pathology
• What is Holmes-Adie pupil?

  Dilated pupils

  Light -> minimal constriction

  Accommodation -> some constriction

  Ciliary ganglion damage
• What is Argyll-Robertson pupil?

  Bilateral irregular small pupils

  Light -> no reaction

  Accommodation -> constriction

  Due to tertiary syphilis
• What are the pupils like in Horner's?

  Small

  Light -> constriction

  Accommodation -> constriction

  Due to sympathetic chain damage -> ipsilateral ptosis & anhydrosis
• What is ptosis?

  Drooping or sagging of the upper eyelid
• What are the pupils like in 3rd nerve palsy?

  Big pupuls

  Light -> no reaction

  Accommodation -> no reaction

  Ptosis & eye deviated down & out
• How do we turn electrical signals from the optic nerve into 'what we see'?

  Electrical signals travel along optic nerve -> thalamus (LGN) -> occipital lobe
• How does 'what we see' coordinate eye movements?

  Occiptial lobe sends projects to brainstem nuclei (superior colliculus, EW nuclei, III, IV & VI nuclei) -> signals to extraocular muscles -> pursuit movements or accommodation movements -> reflexes 
• How do we stabilise our gaze?

  Vestibular nuclei feed into the visual system
• What is the ventral stream responsible for?

  Recognition of objects

  Facial recognition

  Colour memory
• What is the dorsal stream responsible for?

  Spatial awareness

  Looking for things
• What is the frontal lobe responsible for, in terms of vision?

  Voluntary eye movements
• Describe unconscious vision.

  Inputs from optic nerve -> several nuclei in the brainstem -> frontal lobe -> causes movement 

  ^^ Used quite often when driving (esp. when driving to work or driving the same route very regularly) 

  Also quite spooky…

  If you have someone who has bilateral cortical blindness (bilateral strokes) -> lost all vision -> if you put a big letter on a board & hand them a piece of paper and a pen, they can copy what is on the board -> from the unconscious vision reflex 
• Fill in the blanks

  A) Unilateral vision loss

  B) Bitemporal hemianopia

  C) Right homonymous hemianopia

  D) Right inferior quadrantanopia

  E) Right superior quadrantanopia

  F) Right homonymous hemianopia with macular sparing