Before 1960s, all of the photos from water are through plane, that is to say opening a port on waterproof case for shooting( that is why lens case in English is called “port”). When we use a micro-lens with a longer focal length, optical defect under water is not a big problem. ( when ray of light get through straight water interface or air interface, all the plane will be reflected strongly.) The angle is bigger ( lens angle is wider), the problem is more serious. All of these problem will be more serious when it is closer to the corner of photos.
When ray of light gets through a plane lens case at a vertical angle ( a 90 degree angle between water interface and air interface) without refraction, there will no above-mentioned problems. That is the birth of optical dome lens hood. It makes all angles get through lens hood at a vertical angle, actually, this is the way that dome lens hood solves all problems. Arc-shaped lens hood means wider angle of shot, but compared to lens hood, ray of light still gets through lens hood at a vertical angle. That is why the position of dome lens hood ( well-matched length of extension ring of lens hood) is vital.