I have often given presentations at Vets North and Vets South on nursing the ophthalmic patient. “What nurses should know about the anatomy and physiology of the eye” perhaps or “Ophthalmic surgical nursing” or most recently “Nursing the ophthalmic patient”. But when I was asked to write an article for Veterinary Practice on that last topic, it occurred to me that I had never actually asked the nurses I work with what they thought were the key points to be made in such an article. So, thanks to them for their input – though of course any omissions you might note are my fault not theirs!
The two key issues in dealing with any ophthalmic patient in a veterinary clinic are dealing with a blind animal and those with ocular pain. The fundamental way of dealing with such animals is really just an extension of what you would do with any animal in your care: quiet gentle handling with a reassuring voice and touch letting the animal know what is happening. Oh dear – if that is all there is to say it’s going to be a bit of a short article, isn’t it? Thankfully there is a lot more to say. Perhaps we can start with a quick review of ocular conditions that give blindness and pain, then cover how these affect the welfare of the animal and finally talk about ways of alleviating the problems these patients have.
Conditions causing blindness
We can split conditions causing blindness into diseases which cause opacity in the visual axis, those which damage the retina and then those which stop the optic nerve from functioning. Corneal opacity sufficient to cause visual disturbance can be caused by scarring after an injury or by corneal oedema arising when the corneal endothelium is not pumping water out of the cornea. This might be seen in young animals as an endothelial dystrophy, or in older ones as a degeneration.
In most cases, while it looks very white as we cannot see into the eye, the dog actually often sees out well enough for normal general behaviour. The most important thing is working out whether the oedema is caused by glaucoma (Figure 1), a much more concerning condition. In that case, the episclera of the eye would be red with engorged vessels.
Glaucoma occurs when aqueous outflow is prevented giving a rise in pressure. Treatment either reduces aqueous production or increases outflow through opening new drainage channels. While surgical techniques can reduce aqueous humour production by freezing or lasering the ciliary body, or increasing drainage through an implant, few of these have long-term success. Medical treatments reduce aqueous production, but these are drugs for humans where a reduction of 5 to 10mmHg in the eye is valuable. In canine glaucoma the pressure may be 50 to 60mmHg or higher. We need a drug that can reduce this to below 20mmHg. Latanoprost reduces the pressure down from the 50s to 15mmHg in a matter of minutes where it does work. If you haven’t got it on your shelves, give the owner a prescription but tell them to come back so you can assess how well the pressure has lowered before sending the dog home on the drops. Sadly, even with these drugs long-term success is not guaranteed – sometimes enucleation is the only treatment with certain life-long benefit!
However, red eye can be caused by different conditions (Table 1) and the value of a tonometer is highlighted in these cases, as knowing if the intraocular pressure is high (suggesting glaucoma) or low (suggesting uveitis) can be crucial in determining a treatment plan; atropine to dilate the pupil and reduce the pain associated with ciliary spasm is required in uveitis, but very much contraindicated in glaucoma. There are multiple devices available, but the key thing with whichever device you have is to use it frequently – with every eye case that comes in I’d say – and not keep it in a drawer so that when you come to use it you are unfamiliar with its operation.
As previously mentioned, uveitis (Figure 2) is another condition which can cause ocular redness, in which anti-inflammatories are key and atropine is called for to prevent the iris adhering to the lens. Blindness comes in uveitis when these adhesions, termed synechiae, stop the pupil dilation which enables vision. Using atropine to break down these adhesions is crucial and keeping the animal hospitalised with regular treatment until the pupil dilates is advisable.
Cataracts are another significant cause of blindness in dogs. There is not enough space here to discuss cataract surgery, but it would be good to talk about diabetic cataract. Many diabetic dogs will develop cataracts – the lens enzyme aldose reductase turns sugar into alcohol drawing water into the lens opacifying it. Inhibiting this enzyme can prevent diabetic dogs developing cataracts (Williams, 2017).
Welfare considerations in blind animals
When asking owners for their assessment of their dog’s welfare as they became blind (Williams, 2012), we found that they said that while quality of life (QoL) was reduced as blindness occurred, dogs quite rapidly adjusted to their visual impairment and regained a good QoL. This is something useful to tell owners at a time when they may be more stressed than their pet! Many dogs with retinal degeneration gradually lose vision starting with night blindness and here welfare impairment is far less of a problem than, say, with a hypertensive cat that suddenly goes blind with retinal detachment. The key thing here is to ensure that your vets do a retinal examination every time they see an elderly cat, or one with hyperthyroidism or renal failure, to pick up the early signs of hypertensive retinopathy before the cat suffers a complete retinal detachment. As I said at the beginning, a caring stroke and a quiet voice aid a blind animal in knowing you are there and on their side. Reducing noise levels in kennels is important, but that is something we should always be aiming for, isn’t it? Maybe a pheromone diffuser would be valuable to reduce stress levels in blind animals staying in the clinic but that is something worth evaluating for all animals in what is often a stressful environment.
If you have had a corneal ulcer or even an eyelash in your eye, you’ll know how uncomfortable eye pain can be. We probably under-estimate the pain dogs and cats are in with ulcers or glaucoma. Giving non-steroidal anti-inflammatory drugs as pain relief per os should be a standard treatment for all animals which might have ocular pain, and atropine to relieve uveal spasm in uveitis. There is much more to say, but hopefully this has given you something to think through in improving the welfare of blind animals in your care.