You see Jeff a 10 YO Golden retriever for routine vaccination; no owner concerns, but appears to have visual deficits. What do you do?
Great start. All of you are mentioning history, but what specific things are you looking for?
Ok, lots of great suggestions there! Let's narrow down on one for now – the Maze test. What is this?
Yes! You perform a maze test in light and dim conditions. The dog always bumps into things on the left side. What next?
Really good – very important to ask the owners too about their version of the Maze at home – i.e. new obstacles etc
So how important do you think it is that we continue to investigate this or can we leave it?
Well done! It could be a sign of something much more sinister so we should try and help the owner to find out whats going on.
You start to perform a neuro-optho exam. The menace is negative on the left, positive on the right. What does this mean?
What are the neural pathways involved?
On optho exam the left pupil is mydriatic. Swinging flash light test is positive in left eye. What does that mean?
We call it a negative swinging flashlight test if it is normal (both pupils remain constricted) positive means abnormal.
Ok so now we can look at the fundus of both eyes.
What do you make of these?
Which eye is abnormal and what is the abnormality?
What are your differential diagnoses?
Great. Yes possible DDx: Optic Neuritis, retinal detachment, neoplasia
N.b.Remember glaucoma is unlikely as the optic nerve will cup rather than bulge. Also, optic neuritis doesn't have to be bilateral. Generalised progressive retinal atrophy (gPRA) is not a differential for Jeff.
N.b.Remember glaucoma is unlikely as the optic nerve will cup rather
So poor Jeff's owner is starting to worry now. They want to know whats going on and opt for further tests. What further diagnostic investigations would you like to do?
IOP is 12 mmHg (normal) in both eyes
Which imaging modality is better for soft tissue?
So here is Jeff's MRI. What is your diagnosis?
Brill… can you be even more specific? Which tissue in the retrobulbar area is affected?
Poor Jeff. Now we have to decide on what to do and help the client decide too. What are his treatment options?
Conservative management is one option, but why might it not be an ideal one for Jeff? (Hint: think of the left cornea)
Ok so the client decided to have an exenteration performed (don't worry, this isn't a #DayOneSkill!). What does this involve?
Quick question to clarify:
Consensual PLR is when a light is shone in the right eye the left pupil constricts and vise versa. This means that a consensual PLR from right to left means the left pupil constricts when a light is shone in the right eye.
In Jeff the direct PLR is present in the right eye and absent in the left eye. The consensual PLR in the right eye is absent and present in the left eye. The left optic nerve tumour prevents the light stimulus from the retina travelling down the optic nerve and therefore there is no direct PLR in the left eye and no consensual PLR from left to right. The light follows a normal path in the right eye, giving a direct PLR in the right eye and, due to crossing of fibres, a consensual in the left eye despite the left being blind.
What special concerns regarding anaesthesia or surgical technique must you keep in mind?
Histopathology results revealed an optic nerve meningioma. What is the prognosis for this dog?
Jeff is doing well with no swelling at the surgical site and no neurological signs have developed!