It's horrible to see the physical deterioration, and as for the deterioration in memory ... that is clear to see, yet he has moments of complete lucidity (unlike Alzheimers sufferers) where he comments on his condition with a very clear understanding. Also, he can still recall significant recent events. He is now in a care home (he lived independently up until a few months ago, aged 95). He has said 'I'm not going to leave this place am I?'
He has been extremely restless which is apparently a sign of this condition, and by all accounts he has responded well to anti-depressants which have a calming effect. But I can't help admiring his energy and strong will to live independently.
I'm sure that your father appreciates having you there and everything you are doing for him, even when he can't articulate it.