Eye Eye

been reading a book about cave art, and it talks about common visual hallucinations and so, whilst browsing the net about this I stumbled upon a couple of detailed definitions of things I just take for granted, Interesting stuff, the sort of thing we all experience, but hardly ever talk about to each other.

Floaters are little "cobwebs" or specks that float about in your field of vision. They are small, dark, shadowy shapes that can look like spots, thread-like strands, or squiggly lines. They move as your eyes move and seem to dart away when you try to look at them directly. They do not follow your eye movements precisely, and usually drift when your eyes stop moving.

In most cases, floaters are part of the natural aging process and simply an annoyance. They can be distracting at first, but eventually tend to "settle" at the bottom of the eye, becoming less bothersome. They usually settle below the line of sight and do not go away completely. Most people have floaters and learn to ignore them; they are usually not noticed until they become numerous or more prominent. Floaters can become apparent when looking at something bright, such as white paper or a blue sky.

Floaters occur when the vitreous, a gel-like substance that fills about 80 percent of the eye and helps it maintain a round shape, slowly shrinks. As the vitreous shrinks, it becomes somewhat stringy, and the strands can cast tiny shadows on the retina. These are floaters.

'Phosphenes' are signals from the neurons of the retina to the visual cortex of the brain which are interpreted by the brain as lights and visual patterns, but are not caused by visual light. They can be produced by neurons randomly firing (similar to what causes muscle twitches) and a variety of other causes, including pressure to the eyeball and (less commonly) various diseases of the retina and nerves. Phosphenes are most easily noticed with the eyelids closed, or in a darkened environment. Category:Visual system