But if they were all blind, why would they have eyes in the first place? That doesn't make sense from an evolutionary standpoint.
Well, perhaps the lower species they evolved from had eyes but with climatic and cultural changes, the need for vision became less important to survival, so eyes became less functional but not removed altogether, a more obvious analog to the appendix. After all, we have moles on Earth who evolved from fully sighted creatures but whose own eyes have almost withered away - still present but mostly useless and unnecessary because of their environment.
Or maybe they have eyes because their genetic heritage from the aliens in "The Chase" demanded they have eyes, even if they didn't really need them.
Or what DerangedNasat
All of which is moot anyway, because the whole idea of them being blind appears to have been dropped.