Have you ever noticed something swimming in your field of vision? It may look like a tiny worm or a transparent blob, and whenever you try to get a closer look, it disappears, only to reappear as soon as you shift your glance. But don't go rinsing out your eyes! What you are seeing is a common phenomenon known as a floater. The scientific name for these objects is Muscae volitantes, Latin for "flying flies," and true to their name, they can be somewhat annoying. But they're not actually bugs or any kind of external objects at all. Rather, they exist inside your eyeball. Floaters may seem to be alive, since they move and change shape, but they are not alive. Floaters are tiny objects that cast shadows on the retina, the light-sensitive tissue at the back of your eye. They might be bits of tissue, red blood cells, or clumps of protein. And because they're suspended within the vitreous humor, the gel-like liquid that fills the inside of your eye, floaters drift along with your eye movements, and seem to bounce a little when your eye stops. Floaters may be only barely distinguishable most of the time. They become more visible the closer they are to the retina, just as holding your hand closer to a table with an overhead light will result in a more sharply defined shadow. And floaters are particularly noticeable when you are looking at a uniform bright surface, like a blank computer screen, snow, or a clear sky, where the consistency of the background makes them easier to distinguish. The brighter the light is, the more your pupil contracts. This has an effect similar to replacing a large diffuse light fixture with a single overhead light bulb, which also makes the shadow appear clearer. There is another visual phenomenon that looks similar to floaters but is in fact unrelated. If you've seen tiny dots of light darting about when looking at a bright blue sky, you've experienced what is known as the blue field entoptic phenomenon. In some ways, this is the opposite of seeing floaters. Here, you are not seeing shadows but little moving windows letting light through to your retina. The windows are actually caused by white blood cells moving through the capillaries along your retina's surface. These leukocytes can be so large that they nearly fill a capillary causing a plasma space to open up in front of them. Because the space and the white blood cells are both more transparent to blue light than the red blood cells normally present in capillaries, we see a moving dot of light wherever this happens, following the paths of your capillaries and moving in time with your pulse. Under ideal viewing conditions, you might even see what looks like a dark tail following the dot. This is the red blood cells that have bunched up behind the leukocyte. Some science museums have an exhibit which consists of a screen of blue light, allowing you to see these blue sky sprites much more clearly than you normally would. While everybody's eyes experience these sort of effects, the number and type vary greatly. In the case of floaters, they often go unnoticed, as our brain learns to ignore them. However, abnormally numerous or large floaters that interfere with vision may be a sign of a more serious condition, requiring immediate medical treatment. But the majority of the time entoptic phenomena, such as floaters and blue sky sprites, are just a gentle reminder that what we think we see depends just as much on our biology and minds as it does on the external world.
你有沒有注意到 視野裡有東西游來游去? 看起來可能像隻小蟲 或是透明的污點 而且只要你定睛一看 就會不見蹤影 只要你轉移視線就又會出現 但你可別跑去洗眼睛了! 你看到的是很普通的現象 稱為飛蚊症 這些東西的學名是 Muscae volitantes 就是拉丁語中「飛蠅」的意思 而且正如其名 它們也挺惱人的 但那可不是真的蟲 也根本不是外界物體 相反的,那存在於你的眼球之中 飛蚊看起來像活的 畢竟它們會動又會變形 但它們不是活的 飛蚊這種小東西 會投射陰影在視網膜上 就是在你眼睛後面的光敏組織 可能是一些組織 紅血球 或蛋白質塊 因為它們飄浮在透明液中 就是在填滿眼睛的膠狀液體中 飛蚊跟著你的眼睛一起移動 而且眼睛一停 好像會彈回一點 飛蚊可能不太明顯 通常是如此 但它們越靠近視網膜 就會變得越清楚 就像頭頂有燈的時候 只要你的手越靠近桌面 影子就會越清晰 飛蚊要非常明顯的話 就要看著完全明亮的表面 就像一片空白的電腦螢幕 雪 或是清澈的天空 整面相同的背景讓它們更加明顯 燈越亮,你的瞳孔就會收縮 這個作用像把較大 且光源四散的吊燈 換成比較小的單一燈泡 也能讓影子看起來更清楚 還有另一個視覺現象 看起來像飛蚊症 但其實毫無關連 如果你看到一些小點點的光 在你看明亮藍天時四處投射 你會感覺到俗稱的謝瑞爾氏現象 就某方面來說 這和看到飛蚊的情況相反 這種時候你看到的不是陰影 而是移動的小窗口 會讓光穿透進你的視網膜 小窗口其實是白血球造成的 白血球會沿著視網膜表面的微細管移動 這些白血球可以大到 幾乎填滿整個微血管 讓它們前面的血漿空間擴大 因為白血球裡的空間 較能讓藍光穿透 而一般微血管裡的紅血球則較難穿透 只要這個情況發生 我們就會看到移動的亮光 跟著你微血管的路徑 並隨著你的脈搏移動 在視野理想的情況下 你也許還能看到 一條黑色的尾巴跟在點點後面 這是紅血球 串連在白血球之後 有些科學博物館會有樣本 由藍光螢幕組成 讓你能看到這些藍天小精靈 比你平常看到的還清楚 雖然每個人的眼睛都會碰到這些作用 但是數量和型態會大不相同 飛蚊症的情況 通常會不被注意 因為我們的大腦會學著忽視它 然而數量太多 或是太大的飛蚊 若是會阻礙視覺 那就可能是更嚴重的疾病徵兆 需要立刻做治療 但是通常眼內的現象 像是飛蚊和藍天小精靈 只是溫柔地提醒我們 自己看到的東西 也同樣需要取決於我們生理和心理 就和外在世界的影響一樣重要