Aocs 1966
Rods are at the center of the retna in the eye. Rods provide high visual acuity during bright light situations. The ability to read the 20/20 on the eye charts is due to the rods in our eyes. The rods are extremely oxygen rich. The cones surround the rods, the cones are much more light sensitive, but have very low visual acuity and provide are night vision capability. The cones also provide our peripheral vision. When oxygen flow to the eye is reduced, the rods loose the ability to operate. This causes the loss of color vision, then the loss of center vision (it is like looking around a solid vision blocker). While pulling G’s and cutting off blood flow to the head, first your rods will start to have reduced capability, and vision will go black and white, then the hole will appear, and finally around 5.0 G’s there is not enough oxygen to have vision. At night after your eyes have night adopted in about 30 minutes, only the cones work and there will be a hole in the center of your vision. Source Navy Aviation Physiology class Sept 1966