A Navigator isn't plotting "courses" and "looking ahead" to see if his ship arrives and survives 24/7/52. Whatever their normal environment—out of their tanks—is like on their Heighliners, they surely have to use their eyes to get around.
There's nothing to indicate that they were blind, or that they used prescience just to move around their environment, or that they had developed some sort of sound-based positioning capability like bats. To me that means that their eyes, however small and "rodent-like", were still functional. YMMV.
I have heard of only one mistake that doesn’t have an explanation for a careful reader...with an open mind. (And, no, I’m not going to tell you what it is!) —KJA
I don't like every writer's style; for instance, I have never been able to get through Ursula LeGuin, China Mieville, or Iain Banks, all of whom are critical darlings. —KJA
I...had written a bunch of Star Wars and X-Files books...that proved not just that I'm a hack, but that I could write in somebody else's universe... —KJA