Vision Pathology Flashcards
Draw out the optic visual pathway, and indicate the possible sites of lesions + what their respective losses of vision would appear like.
- Monocular blindness
- Bitemporal hemianopia
- Nasal hemianopia
- Homonymous hemianopia
- Homonymous hemianopia with macular sparing
What are the four types of refractive error defects?
- Myopia
- Astigmatism
- Hyperopia
- Age-related presbyopia
How does myopia work?
- Axial length is too long / Lens refractive power is too high
- Distant objects appear blurry
- Corrected with divergent spectacles
How does hyperopia work?
- Axial length is too short, leading to images being focused behind the retina
- Near / Distant objects appear blurry
- Corrected with convergent lens
How does age-related presbyopia work?
- Lens accommodation reflex gradually declines with age, leading to poor image focusing
- Near / Distant objects appear blurry
- Corrected with convergent lens
How does astigmatism work?
- Cornea / Lens is not fully round, leading to two different convergent radii
- One spot of light is focused into two lines + a blur
What are the four visual acuity defects?
- Vitamin A deficiency
- Macular oedema / Submacular Haemorrhage
- Rod-cone dystrophy
- Retinal detachment
How does vitamin A deficiency affect visual acuity?
- Rods depend on vitamin A
- Loss of night vision
How does macular oedema / submacular haemorrhage affect visual acuity?
- Loss of visual acuity
How does rod-cone dystrophy affect visual acuity?
- Dysfunction in protein required for rods and cones
- Loss of function
How does retinal detachment affect visual acuity?
- Retina detaches from RPE
- Loss of function
What CN lesions affect which extraocular muscles?
- A3 SO4 LR6
- CN III - All
- CN IV - SO
- CN VI - LR
What does a CN IV lesion result in?
- Superior Oblique affected
- SO normally intorts (minor - outward movement, medial depression), so at rest, eye extorts outward and upward
What does a lesion of CN VI do?
- Lateral rectus affected
- LR normally performs outward movement, so a lesion leads to inward deviation
What does a CN III lesion affect?
- All eye muscles except lateral rectus and superior oblique, leading to outward and downward deviation of eye
- Levator palpebrae superioris, leading to ptosis
- Parasympathetic fibers, leading to mydriasis
What is anisocoria?
- Abnormally-sized pupil; large or small
How does an abnormally-large pupil arise in anisocoria?
- More apparent in light, due to parasympathetic failure
- CN III lesion (pupil constricts with 1% pilocarpine) / Adie’s tonic pupil (pupil constricts with 0.1% pilocarpine)
How does an abnormally-small pupil arise in anisocoria?
- Sympathetic failure, more apparent in the dark
- Horner’s syndrome
How does internuclear ophthalmoplegia occur?
- Lesion of medial longitudinal fasciculus, which coordinates both eyes’ conjugated abduction / adduction
- Leads to one eye not responding to lateral movement / response being slow (demyelination)
