The WordReference page for "perte" tells me that "à perte" means "at a loss", and "à perte de vue" means "as far as the eye can see". (It also tells me that "perte" means "loss").
If I try to translate "à perte de vue" literally, then, it would mean "at a loss of sight" or "at sight's loss" or "at the loss of the panorama (panorama = landscape that we can view)". I don't see how these translations can suggest "as far as the eye can see"! (If anything, I would have expected an expression that translated to the opposite of loss (such as "to the full degree of possible sight") to mean "as far as the eye can see"!)
Is there a way to understand "à perte de vue" as made up of "à perte"?