Anyway, I've got him again, and once again there is clearly something very wrong. This time it's his right eye, which is badly infected. I am thinking this is a side-effect of the circulatory problems associated with diabetes.
Immediately I saw the cat I was thinking 'Why don't you acknowledge this problem?' It's obvious something is badly wrong. Anyway as soon as I had 'custody' of the cat, I whipped him off to my own vet. She says his eye is so bad that she would probably remove it except that he wouldn't survive anaesthetic. But as far as I can tell he is not suffering. I don't think he can feel it. There seem to be none of the tell-tell signs of pain; he's purring loudly, lets me touch the eye without flinching, and eating three or four big meals a day. Therefore I am starting antibiotics and anti-inflammatory to try to save the eye without surgery.
Eating 3 or 4 big meals a day? - bonus vet advice - he is also hyperthyroid. The vet says balancing treatments for hyperthyroidism and diabetes would be 'demanding'. If I start him on a big thyroid work-up while they are away I am committing my parents to a great deal of stress. I know I underestimated them before, but I don't think they could cope. Unlike the diabetes I don't feel his thyroid problem is harming his quality of life - if you saw him, he's a happy but very very old cat. The vet says without radical treatment his life expectancy is - well, pretty short.
So, my proposal is to not to start on a third regime on top of the insulin and eye treatment (both of which I have imposed on them without asking) but to simply let my mum and dad know the diagnosis. Then they can decide what to do. I think the only alternative would be to - I don't know - claim custody of the cat, refuse to give him back, and start some massive intervention. I think it's better to let them look after him at their home, where he is with people he has known all his life, and will probably pass away quite peacefully and quite soon.