Visual Pathways Flashcards
What is visual acuity and how would you test for it?
Ability of the visual system to distinguish a gap between 2 objects
- Snellen’s chart: stand 6m away and test one eye at a time, recorded as distance (m)/ x (line of smallest text read)
- LogMAR test chart: stand 3m away, test one eye at a time, recorded as a number
What are the advantages of the LogMAR chart over Snellen’s chart for testing visual acuity?
- there are the same number of letters on each row
- the spacing between the letters are proportional to its size (decreases ‘crowding’ effect)
- equal logarithmic changes in size of letter and all equally as easy to read
If a patient is unable to read the largest letters on Snellen’s chart?`
- half the distance (3m, then 1m)
- ‘tell me the number of fingers I am holding up’
- ‘follow my hand movements’
- light perception
Define the scores for a blind and partially sighted patient, and the visual acuity required for driving
- blind: less or equal to 3/60
- partially sighted: over 6/60 - 3/60
- driving: over or equal to 6/12
Describe the pupillary constriction reflex arc
- light comes into eye and travels in optic nerve
- info crosses over in optic chiasm, synapses in LGN
- travels to brainstem to ciliary pre-tectal nucleus
- passes to Edinger-Westphal nucleus bilaterally (consensual reflex)
- nerve responds to ciliary ganglion
- short ciliary nerve innervates iris and causes pupillary constriction
What would you look for and test when examining the pupils?
- observe for changes in size, shape or colour (efferent problem)
- light reflexes (check for consensual)
- check for RAPD (afferent problem)
- look at far then near object for miosis
What are the causes of a RAPD?
- retinal detachment
- optic neuritis
- anterior ischaemic optic neuropathy (vascular)
- tumour pressing on the optic nerve
What things are you looking for in the fundal reflex test?
compare eyes for:
- brightness and colour (red/white eyes)
- any dark patches or absence of reflex
- position of corneal reflections
What things are you checking for in direct opthalmoscopy?
- optic nerve (margin, colour cup)
- neuroretinal rim (pale or opaque = atrophy)
- any new vessels (diabetic retinopathy)
- disc swelling ( pseudo = small disc, Ca2+ deposits, genuine = optic neuritis, increased ICP)
- retina: 4 quadrants
CN III palsy
- vertical diplopia
- eye is ‘down and out’
- pupil dilation and ptosis
CN IV palsy
- oblique diplopia
- head tilts away from side of lesion
- diplopia worse looking away from side of lesion
CN VI palsy
- horizontal diplopia
- worse in distance and towards side of lesion
Describe the pathophysiology of diabetic eye disease
- chronic hyperglycaemia
- glycosylation of protein/basement membrane
- loss of pericytes
- decreased O2 transport leading to tissue hypoxia
- vasoformative factors produced
- neovascularisation and leakage
- haemorrhage, retinal detachment and glaucoma
- loss of sight
