The  rods  and  cones  (film) of  the  retina  are  the receptors  which record  the image and  transmit it  through the  optic nerve  to  the brain for  interpretation. Rods and Cones Fovea (All Cones) Cones active Area of best day vision Rods active Night blind spot Area of best  night vision Lens Retina Optic nerve Iris The  pupil  (aperture) is the opening at  the center of the  iris . The size of the  pupil is adjusted to control the amount  of light entering the eye. Pupil Light passes through the  cornea  (the  transparent window on the front of the  eye) and then through the  lens  to  focus on the retina. Cornea Rod concentration Figure 12-6. Rods and cones. After the eyes have adapted to the dark, the entire process  is reversed when entering a lighted room. The eyes are fi rst  dazzled by the brightness, but become completely adjusted  in a few seconds, thereby losing their adaptation to the dark.  Now, if the dark room is reentered, the eyes again go through  the long process of adapting to the darkness. Before and during night flight, the pilot must consider the  adaptation process of the eyes. First, the eyes should be  allowed to adapt to the low level of light. Then, the pilot  should avoid exposing them to any bright white light that  would cause temporary blindness and possibly result in  serious consequences. Temporary blindness, caused by an unusually bright light,  may result in illusions or afterimages until the eyes recover  from the brightness. The brain creates these illusions  reported by the eyes. This results in misjudging or incorrectly  identifying objects, such as mistaking slanted clouds for the  horizon or a populated area for a landing field. Vertigo is  experienced as a feeling of dizziness and imbalance that can  create or increase illusions. The illusions seem very real and  pilots at every level of experience and skill can be affected.  Recognizing that the brain and eyes can play tricks in this  manner is the best protection for flying at night. Good eyesight depends upon physical condition. Fatigue,  colds, vitamin deficiency, alcohol, stimulants, smoking, or  medication can seriously impair vision. Keeping these facts  in mind and taking appropriate precautions should help  safeguard night vision. 12-6