Visual effects where the stimulus originates from within the eye itself. In humans, the most common entoptics are "floaters", small globules that will slowly drift across your field of vision and may respond to movement of the eyeballs.

An easy although potentially dangerous way to induce such an effect at will is to close your eyes and firmly press inwards on your eyeballs with your thumbs. After roughly 5 seconds your vision will start to fill with random colours which will persist for a few seconds after you stop applying pressure.