Session 5: Case Studies on the Visual System Flashcards
You see a patient with albinism who complains that he is unable to see well in bright sunlight.
Why is this?
Pigmented cell epithelium usually contains melanin.
In albinism the melanin is absent and this causes light to not be absorbed. Instead the light will be reflected and cause a glare.
This is very irritating for the eye and painful.
Give some additional common causes of perception of excessive glare.
Problems with constriction of pupils
Digoxin
Meningitis
Surgery
Astigmatism
Following a stroke affecting her left hemisphere, a patient is finding the she keeps bumping into the wall, usually on her right side.
Name the (probable) defect and draw a diagram of the visual pathway, highlighting where the lesion is.
Right homonymous hemianopia.
Could be either optic tract lesion, primary visual cortex, both optic radiations or lateral geniculate nucleus.
All on the left side
A patient has a pituitary adenoma compressing the optic chiasm.
Name the visual field defect that may result and draw a diagram of the visual pathway to illustrate how this may have arisen.
Bitemporal hemianopia
A patient suffers from homonymous hemianopia caused by a stroke.
How might we determine whether the lesion is in the optic tract or the visual cortex?
Could have macular sparing in primary visual cortex.
If the lesion is of the optic tract then it would not have macular sparing.
Does this hold for non-vascular lesions of the visual cortex like tumours?
Non-vascular lesions usually do not spare the macula.
However they can if the only thing that is compressed is the geniculocalcarine tract.
An 8 year old boy is admitted with fever, neck stiffness, and photophobia. The boy has recently been receiving chemotherapy for leukaemia. Treatment is commenced immediately, but it is noted early on that sensation in the right half of his face is altered and that he has a right homonymous inferior quadrantopia.
Give three differential diagnoses.
Meningitis
Tumour
Subarachnoid aneurysm
Retropharyngeal abscess
The boy has focal neurology, what is the most likely site of the lesion?
Parietal lobe in the left hemisphere.
Laterally and in the postcentral gyrus.
A patient with multiple sclerosis presents to their GP with new onset of diplopia. The GP suspects that the patient has developed a new plaque in the brainstem that has interfered with conjugate eye movements.
In which pathway has this plaque formed?
In the medial longitudinal fasciculus.
Give some examples of how this pathway controls conjugate eye movements.
The CNs of the extra-ocular eye movements all converge here. This is in order to allow them to communicate and work in
coordination.
In the absence or damage of this fasciculus then there will be uncoordinated eye movements and resulting diplopia.
A patient has a tumour arising from the cerebral aqueduct in the midbrain.
How is this likely to affected the accommodation reflex and eye movements in general?
Tumour adjacent to EDW nucleus. This is because cerebral aqueduct can be found close by the EDW nucleus that is concerned with the accommodation reflex.
