Seminar: The Abnormal Pupil Flashcards
How may cataracts affect the pupil?
-> 2* phacolytic uveitis (phacoleaky) as exudes proteins from the cataract
How does posterior synechia appear clinically?
Rough pupil edges
How does glaucoma affect the pupils?
- fixed, mid dilated non responsive
+ episcleral pattern
How will all causes of retinal atrophy appear eventually?
- hyperlucent/reflective tapetum (one zone only, ratehr than equally reflective as it should be)
- atrophied retinal BVs
- dark optic disk
How can ataracts be distinguished from nuclear sclerosis?
- DDO
- cataracts will -> shadow when reflected from behind
- nuclear sclerosis allows light thtough
What are iris rests?
- posterior synechia where the stuck on bits break off
- leave a ring/splodgy ring of pigment = iris colour r black around the lens
What is the only possible cause of pigment being left in the centre of the pupil?
Persistent pupllary membranes
- pupil doesnt constrict enough to leave pigment in the exact centre
What colour are the backs of all irises?
Black
Where do iris cysts arise? Why?
- always arise on BACK of iris
- as made of EPITHELIUM, whih is only present on the back (front = stroma)
What may occour 2* d/t iris cysts?
> free floating anterior uveal cyst if i pinches off and is carried forward in the aqueous humour
- can fill up nterior chamber and block vision (will sink to the bottom)
golden retrievers and great danes cysts can build up behind the iris and push iris forward -> blockage of the ICA and 2* glaucoma
What are the ddx for melanotic growth in the anterior chamber in cats? How cna benign and malignant be distinguished?
- Benign melanosis ->
- Anterior Uveal Melanoma (benign/melignant)
- no way to distinguish benign v. malignant*
How cna progression from benign melanosis to AUM (anterior uveal melanoma) in cats be identified?
- very difficult
- look for hanges in surface architecture as well as colour
- look for pupillary changes at rest and with dilation
Tx AUM?
- enucleation
- but metastassi uncommon and v slow (happens years later) so sometimes best to leave?
- look at speed of progression and age of patient to decide
What sign often correlates with presence of mets in uveal melanoma in cats?
- presence of glaucoma
What pupil changes can be seen with AUM?
- slow and sluggish PLR as iris musculature has been affected
- dyscoria (funny shaped pupil)
What can be given to diagnostically dilate the pupil?
- Tropicamide (short acting version of atropine)
- doesnt affect ciliary body as much as iris
What potential causes can affect PLR?
- synechia
- glaucoma
- PRA
- cysts
- melanoma/cytoma/iridoepithelial adenoma/sarcoma/lymphoma
What is the Marcus-Gunn sign? What does it indicate?
- absent direct PLR, and no response in other eye when affected eye tested
- consensual PLR still present when unaffected eye tested
> indicates damage to retina or pre-chiasmal optic nerve (afferent only) - retina, optic nerve head, optic nerve
Outline the visual pathway
- retina, optic nerve, chiasm, optic tract, lateral geniculate body (brain), optic radiation, cerebral cortex
What does menace test?
- vision
- a prechiasmal lesion should have no menace response on affeced side
- NB. do not elicit blink by touching hairs/creating a draft
What types of reflex is PLR? Where is the pathway?
Subcortical
- travels sae as visual pathway past chiasm and for a short distance in the optic tract
- pretectal nucleus
- Edinger-WEstfal Nuclei (?)
Why is Marcus Gunn sign not seen with unilateral glaucoma?
???
- fixed pupil seen with glaucoma
What may affect the PLR that is not of neural basis?
- catecholamine release
- iris problems
- senile iris atrophy (rough jagged edges of iris around pupil)
- posterior synchiae
What do post-chiasmal lesions of the visual pathway cause?
- “central blindness” (even though not necessarily in the brain)
- hard to pinpoint location if post-chiasmal
How do the visual fields relate to the optic tracts?
- right visual field is detected by left hemisphere in both eyes and is carried as the left optic tract
- left visual field is detected by right hemisphere in both eyes and carried as right optic tract
What is hemianopia?
Single optic TRACT affected -> loss of one visual field (not one eye!!)
- NB: will be the opposite visual field to thhe damaged tract
Potntial causes of central blindness?
- neoplasia
- MUO/MUE/GME (meningtis or unknown origin)
- post anaesthetic ischaemia (cortical necrosis) in cats
> if concurrent signs - imaging/neuro consult!!
Do anterior uveal cysts block ICA?
No
What signs make you suspicious of more malignant melanoma?
PLR and dyscoria
- indicate deeper muscles affected
What are the 2 potential causes of an abnormal pupil?
- iris
- PLR pathway
