Has anyone investigated the "improve your eyesight with exercise" claim?

I’ve reached that magic age – my eyesight has dramatically gotten worse. I know that it’s due to a hardening of the lens, making it more difficult for the muscles used for focus to function effectively. It makes sense to me that glasses could result in a worsening of the effect since the muscles would not have to work as hard and might even lose tone. Is it possible that exercise could delay the progression? (I know, I know, reading glasses are in my future.)