The condition mainly affects the retina, a layer at the back of the eyeball that picks up light and sends that info to the brain, where it's translated into images. (businessinsider.com)
The human retina is a patch of nervous tissue in the back of the eyeball half a millimeter thick and approximately two centimeters across. (scientificamerican.com)
This redness results from light reflecting off blood vessels in the retina, the light - sensitive layer of tissue lining the back of the eyeball. (scientificamerican.com)