On a mission to Mars that takes three years, the astronauts can start to have vision problems. The fluids in the body go up to the head because of microgravity which puts pressure on the optic nerve. A sheet of nerves is responsible for vision in the retina. The blind spot is both on the right and left eyes. My Idea is to use the blind spot test. To know if the test is successful depending on which eye that is covered, the CIRCLE or the X will disappear and then come back. You need to hold the bar at arm's length. The X is on the right side and the CIRCLE is on the left side. You need to focus on the X and close your right eye. Then slowly bring the bar in closer to their face.Then do the same with the other eye.