I had my first OCT scan at the opticians this morning. The infra-red scan mapped out a small area at the back of my eye and rendered it in 3D, reminding me of the 3D modelling I’ve experimented with in programs like Bryce and Vue.
A shallow crater is where the cone cells for daylight vision are concentrated. These are particularly sensitive to movement but they’re useless in the dark so as the iris opens to let in more light a wider spread of rod cells takes over, with the crater of cone cells becoming a bit of a blind spot.
This explains why when observing a faint object in the night sky, such at the Andromeda Galaxy you have to do that trick of looking slightly to one side of it. It’s too faint to register on your array of cone cells.
My true blind spot, the spot where blood vessels and nerves enter the eye, looks less like a crater and more like a corrie surrounded by glaciated peaks.