I think that other Cavalier here who has brittle nails and suffers from nail loss is my Holly Poppet. She very definitely has dry eye/curly coat syndrome.
I really don't wish to argue with your opthalmologist, but what you say in your post indicates this disease.
My Holly's coat is only partially affected by the roughness and standing on end symptom - so much for the coat needing to be rough and wiry.
I think you should ask your vet for Optimune ointment to apply to the eyes twice daily to stimulate tear production, plus Lacrilube ointment to lubricate the eyes. The presence of corneal ulcers without evidence of injury or other disease is also an indicator of CC/DE Syndrome.
So far as the brittle and detaching claws are concerned, this is a another indicator of DE/CC. Holly has a deformed front paw, in that she has two paws attached to the same leg, plus the deformed and brittle nails, which sometimes get caught in the carpet and are torn out when she tries to free them.
Infection is the enemy of any auto immune disease, which applies to CC/DE, so if blood is drawn when the nail is detached you will need to make up a saline solution of 1 tsp of salt to a pint of warm water and plunge the whole paw into it and leave it there for a minute or so, despite the protests from the Cavalier, then carefully dab the whole paw dry with a clean, unused towel or similar material. I keep a set of face flannels in the linen cupboard especially for Holly. I think that dogs with this problem are better walked only on grass, not the road or the pavement, as poor little Holly would be walking on the flesh of the paw pads if I walked her on concrete, causing abrasions which may lead to infection.
I am sorry if this post comes over as being a little abrasive - I just looked in here quickly before going to Crufts, and never expected to get caught up in anything like this, so please don't think I mean to be abrupt, just rushing to sort out my dogs and head for NEC. I will be back on tonight and hope to be a little more tactful and thoughtful in what I say and how I say it.