system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly are the purple and green dots I see, after looking at a bright light too long? How can I still see them when I close my eyes?
gpt
Ophthalmic technician here. Those dots are called negative after-images. When you look at a light or image, that image is received by light sensors in the retina called rods and cones. The light sensors then pass the image to the brain. The reason you still see them is that after you have been looking at the light or image for about 60 seconds, the rods and cones begin to fatigue and when you look away or close your eyes, you are seeing the negative color or whatever object you were looking at.