Problem solving - abnormal pupil Flashcards
What does nuclear sclerosis need to be differentiated from and how?
Cataracts with DDO (look for retroillumination)
Broad principles - cataract sx
Make small incision into lens capsule, remove the contents of lens, put implant within lens capsule
What is a cyst?
a free-floating anterior uveal cyst (i.e. moves to anterior chamber with aqueous humor). Note that these don’t float to iridocorneal angle and cause cataracts.
Tx - free-floating anterior uveal cyst
- aspirate
- laser burn (but risk of causing cataracts)
What is AUM in cats?
= Anterior Uveal Melanoma
- It is what benign melanosis leads to.
- When the change happens is hard to define
When may feline benign melanosis lead to AUM inc ats
- look for changes in surface architecture, not just colour
- look for pupillary changes at rest and with dilation (i.e. when it affects the ciliary and other mm, the benign melanoma is transitioning into a malignant melanoma. At this point you can’t be sure how soon a metastasis will occur). example = dyscoria
- presence of 1st makes it suspicious, the 2nd confirms it
- presence of glaucoma indicates metastases are already likely
Tx - feline benign melanosis
Enucleation (usually) BUT metastasis is uncommon and happens years later. Look at speed of progression and age of patient to make decision.
T/F: not all PLR abnormalities are due to tumours
True, can also be caused by:
- synechia
- glaucoma
- PRA
What does the Marcus Gunn sign indicate?
A prechiasmal lesion - i.e. in the optic nerve or in the retina or optic nerve head. It is a unilateral, afferent lesion
Where is the lateral geniculate body (LGB)?
Located within brain but remember that diagrammatically and functionally is not in the cortex.
What does the menace response test?
Tests whole visual pathway as it is a learned response so requires cortical processing
What should you remember when doing a menace response?
don’t elicit a blink response by touching hairs or creating air flow that contacts the cornea
Describe a Marcus Gunn sign (i.e. of a prechiasmal lesion)
should have NO menace response on the affected side. The PLR should confirm this as it is not associated with the brain, well brain but not cortical so absence is not a brain problem).
” A Marcus Gunn sign: A prechiasmal lesion with have no direct PLR in the affected side or indirect from affected to unaffected but will have normal direct PLR in the unaffected side and a normal indirect from the unaffected to affected side. “
This is because the PLR is processed in the Edinger Westphal nucleus outside the cortex.
Why doesn’t a Marcus Gunn sign/prechiasmal lesions lead to a unilateral glaucoma?
due to a fixed mid-dilated pupil
What might affect the PLR other than a prechiasmal lesion?
- catecholamine release
- iris problems : senile iris atrophy or posterior synechiae
What is senile iris atrophy?
Something that occurs with age. Seen well with retroillumination (ragged pupil edge)
What happens if a lesion is post-chiasmal?
- Central blindness
- More difficult to pinpoint after cross-over of fibres
Define hemianopia
blindness over half the field of vision
What happens if there is a left optic tract lesion (i.e. post-chiasmal)?
there will be RIGHT visual field loss
How do you determine the location of a lesion that is post-chiasmal causing central blindness?
More difficult to pinpoint than pre-chiasmal.
If with other CS, you must refer to neuro and imaging, possible Ddx include:
- neoplasia
- MUO/MUE/GME (Meningitis of Unknown Etiology)
- post-anaesthetic ischaemia.
What is the difference between a mild form of PPMs and posterior synechiae leaving iris rests?
PPM - leaves central part of pupil
Iris rests - affects eccentric part of pupil therefore it cannot constrict to a small point.
What does glaucoma present with?
Glaucoma presents with a fixed mid-dilated pupil, pressure
damage to the retina and optic nerve head. T
Why does an anterior uveal cyst form?
They are cystic
structures that form when, for some reason, a
sheet of cells of the posterior iridal
epithelium or the ciliary body epithelium
pinch off the surface and form a ball-like
structure that is filled with aqueous humor
