Went to the vet today to have various Jake aspects examined.
Vet says his eyelids look somewhat reddish and irritated, the right one perhaps slightly more than the left, but probably nothing serious. Gave me some anti-irritation ointment to apply for a week. He said that the retinas look fine; a little graying in the lenses that's normal for his age and not cataracty. He had an interesting and simple test to check his vision: With his hand about a foot away from Jake's head, he moved it suddenly towards Jake, just a twitch of an inch or so, but Jake blinked each time, with the hand moving quite a ways around the head.
Ears looked OK, but one had a big plug of wax. Vet says that's probably not enough to cause major distortion of hearing, but try applying ear ointment/cleaner for a few days and really massaging it and see whether it makes any difference. He did say that almost all dogs, between 12 & 13 years, start to lose their hearing. And regarding Jake's sometimes-active-response and sometimes-no-response--could be the pitch of the sound as much as the volume. (Like my dad's hearing, for example.)
Any other testing of vision and hearing is much more expensive and can probably be done only at the vet school at Davis. Don't know that I want to know that badly what's going on ....