I suppose it really depends on the context, environment and motivation (it was very tempting to say, "purpose") of “closing the eyes”. When I close my eyes simply for the sake of closing them, the immediate experience comes from the suspended particles in the air stuck onto the retina. I see them as irregular chain of sausages descending down on an unpredictable path. A (senior) friend calls it "cosmic tetris" only that the blocs are no longer in your control...
When I am lying down at bed time with eyes closed, about to doze off, images start taking shape from “garbage thoughts” arising from the semi-conscious mind. This however doesn’t happen too often (and I am sure there is a proper technical term other than the one in context of depression for what I called "garbage thoughts"). Essentially I'm trying to refer to - incomplete or half-backed thoughts / ideas; or ideas that my conscious mind has “rejected” due to certain “reasons”; or thoughts that were utterly nonsense yet remained as residual of something within the scope of the mind. At times it become easy to capture and decipher them when you suddenly come back waking up from your dozing.
And I wistfully intend to consider them as “waste-disposal” from the conscious mind after a certain hectic activity that it has performed. I further tend to believe them "spent" because they hardly ever repeat themselves or those acts.Whilst concentrating with my eyes closed, I might see images of entities related to the “thought” that I am concentrating about. The thought itself should be fixated, for that is the purpose of the concentration, and my consciousness ensure that for me. (The word, thought, is important here I suppose for our consciousness cannot hold onto a physical object but only chit-subjects - an idea or a thought.) Here the attempt would be to consciously channelise information related to the thought under focus - a train of thoughts (illustrations) linked together with "logic".
Its only when I tend to drift from conscious concentration to the beginning stages of meditation that the real circus begins. A few years ago under the strict scrutiny of my hon. master when I learned practicing meditation, it always began with concentration on a certain prescribed “thought”. The thought is then glorified so to speak, say, by being plunged into complete chaos and randomness such as raising it a few miles in the sky and then suspending it in mid air.
And there she goes… As an example the thought sometimes becomes a comet as it were charting its own course and highlighting the cosmic realm that is absolutely dynamic and constantly in motion. All you have to do is to follow the comet and enjoy the ride ;-) On other times you sit on the wave of the musical water-bowl rising at the centre and spreading with the music outwards (do try sometime to capture the marvelous experience of mediation with musical water-bowls). And on yet another day, it would...