Most of what we do see with our eyes is a reflection. Any light from a bouquet of flowers is just reflection. Looking through a bottle shows beside reflection some refraction. The only exception, where we don’t see reflected light is e.g. offered by an open fire or a light bulb. The sight of a star also shows direct light, which is usually subject to refraction due to the atmosphere.
Our eyes seem to absorb the light when we see. In fact, they can also reflect the incident light. We know this phenomenon from cat images that we have mistakenly photographed with a flash light.
Sitting in front of me my right eye is on the viewers left side and the left eye is on its right side. The instrument uses a red and a green laser at a harmless energy dose.
With different wave lengths of a laser an ophthalmologist is able to see different structures of the fundus and uses this property for diagnostic purposes. Looking at the green color only that stems from the green laser, the result is a monochrome image that shows vessels of the surface of the retina and smalls nerves joining the papilla.
Looking at the red channel displaying the reflections of the red laser light, monochrome images show deep vessels behind the retina.
Beside the medical point of view there is an aesthetic one, too. Dr. Gösele, to whom I owe these beautiful pictures, confirmed to me the impression of an astronomical night shot, which other viewers also feel. With a courageous crop you get there:
This is how the central part of my sensor looks like when creating photographs or X-rays. My wife immediately urged me not to fall into a narcissistic trap ….