We’re halfway through our ophthalmic series presented by Ron Ofri DVM PhD DECVO, preceded by the August webinar about the Anatomy of the Fundus. That’s an almost essential pre-watch if you’re thinking of watching this webinar, how else are you going to understand the abnormalities that can occur? It’s not a massive task though, because all of Ron’s webinars are fascinating to watch and his enthusiasm is infectious. He breaks down the topics into easily understandable chunks. The images and cartoons that are on the slides make everything easy to remember as well!
Do you see it?
History & Clinical Exam
The first part of this webinar on sudden blindness- the first ‘section’, I suppose – is focused on history and clinical exam.
It starts off by emphasising the importance of a good history. Not just that, but a history which doesn’t lead the owner down a predetermined path. This means instead of asking ‘can your pet see at night’, asking ‘are there any differences between your pets vision in darkness and light?’. Other important aspects of the case to determine is the onset of duration (was it a sudden blindness or a gradual onset?) and the animal’s general state of health. A cat that’s been circling after being hit by a car is going to have different differentials to a collie that’s gone suddenly blind.
The second part of your process should include a clinical exam, as is routine. In an optical exam, essential tests include the PLR, and the consensual PLR, as well as the dazzle reflex. These are broken down into their neurological pathways and whether the results mean the animal is visual or not. After all, if a dog has a normal PLR or dazzle then surely it means they’re visual? Ah hah! But no, it doesn’t because they’re subcortical reflexes. Even with advanced cataracts, these reflexes will still be present.
Your neurological test results will determine what your investigations and differentials are. There’s a handy table that Ron created, which becomes our template through the rest of the webinar.
Getting to the bottom of things:
First thing you should know about retinal haemorrhage? That it’s a clinical sign, not a diagnosis. In a normal patient, as you know, there’s no ‘normal’ amount of blood that pools on the retina. Ideally you get a nice clear retinal image with no blood outside of the vessels! Retinal haemorrhage is of the top three categories of reasons for acute blindness, and you can easily spot it with a simple ophthalmoscope. Getting to the bottom of it is a bit more challenging, and Ron gives us some great tips on what to search for to find the primary cause.
A hypo-reflective tapetum can be a sign of retinal inflammation, and as the complications can include detachment, its something that’s important to recognise and put on the list for acute blindness. Signifying retinal or sub-retinal oedema, you can spot it by the presence of perivascular cuffing. Another clinical sign that we have to investigate, as before you treat posterior uveitis you have to look for the systemic cause. The webinar covers how to do this as well.
Usually remaining attached at the ora serrata and the optic nerve head, the pathogenic “seagull sign” can result from an accumulation of sub-retinal fluid. This can be either exudate or haemorrhage. Retinal detachment can also occur secondary to traction (so called “traction detachment”) or rhegmatogenous detachment. The treatment and investigation of retinal detachment varies depending on whether it’s rhegmatogenous or non-rhegmatogenous. Unfortunately, these cases of sudden blindness can often end in enucleation. The treatments and management are delineated clearly in the webinar by Ron Ofri.
It’s more than meets the eye…
Finally, Ron Ofri covers SARDS – Sudden Acquired Retinal Degeneration Syndrome. This is an unfortunate syndrome that develops over days and is often preceded by a history of systemic signs. These systemic clinical signs can mislead clinicians into alternative diagnoses, so Ron Ofri shows us what to look out for in the webinar and how to not fall into that trap! Unfortunately the blindness and degeneration is permanent, so there is no treatment. We’re directed to some pages that owners may reference, as well as papers which are great for further reading.
My oh eye
This was another wonderful webinar by Ron Ofri and a great addition to his growing library of ophthalmoscopic lectures. Opthalmoscopy in clinical practice is often limited to diagnosing ulceration, conjunctiva, and glaucoma, so it’s a great opportunity to expand your knowledge of causes of sudden blindness and be prepared for the future. You can also catch Ron and his co-authors of Slatter’s fundamentals at our Virtual Congress 2021 – which you can check out here.
Let us know what you thought about this webinar in the comments below!