As rickair says, if it is progressive (ie., glaucoma or something) it’s an issue because even if it’s OK now, it’s not what you want to START a career in this business. But if it’s static - ie, just the way God made you - then it all depends on the extent.
Except for the central point of fixation and maybe 20 degrees to either side, everyone’s vision is pretty, delta Sierra (as in 20/30 and dropping fast). 40 degrees off the visual axis most of us would be hard pressed to see a wide body at five miles without relative motion. Peripheral vision is more just a moving object locator for the central vision enabling you to swivel your eye to bring the central 20/20 (or better) to bear. A good scan can cover a multitude of sins and if your peripheral vision deficiency is truly static...well, the FAA has approved quite a few one-eyed pilots (Whose nose alone takes out a huge chunk of what peripheral vision they have left) so they aren’t particularly unreasonable if you have demonstrated that it hasn’t been a huge issue.
