Different cause. Floaters are debris suspended in the vitreous which can be seen in the proper light if they are near the central visual axis. Entoptic phenomena are natural and interesting objects in the visual view - the most common being the "flying corpuscle" view of your actual blood vessels in the center of the back of the eye. They are not pathologic.
Floaters. Floaters would be a cause of what they refer to as entoptic phenomena. Entoptic phenomena are visual effects whose source is within the eye itself. Floaters are blurred areas of jelly withing the eye causing visual affects most commonly referred to as "floaters".
Yes. Vitreous is the jelly-like substance in the middle of the eye that undergoes normal changes with age and peels off the retina in the back of the eye. Debris in the vitreous (like blood) or clumping of the vitreous blocks the light passing through the eye; these perceived shadows are floaters. Entopic phenomena are flashes of light that occur as the peeling vitreous tugs on the retina.
Normal v. abnormal. Entoptic phenomena are patterns and sensations which are part of the normal visual system which is not perfect. Floaters are objects introduced into the visual axis which can be seen in certain light circumstances. While floaters are not usually harmful, they can be annoying and may be a first sign of a problem. Consult with your ophthalmologist to sort these out.
Entoptic= (internal- Optical) entoptic phenomenon are any optical images that are generated internally from within the eye. These are usually due to traction on the retina, movement of cells in the fine retinal and choroidal vessels, and movements of debris and particles within the vitreous. So one type of entoptic phenomenon is a floater. If you are experiencing such symptoms, get a retinal exam.