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.
你是否会注意到自己的视线中有漂浮物? 它看起来像是小虫或者透明液滴 但当你想要更仔细地看它的时候 它又消失了 转换视线之后 它又会出现 但你别去冲洗眼睛! 你看的其实是一种常见现象,飞蚊症 科学界称之为 Muscae volitantes 是拉丁语中飞蚊的意思 物如其名,它们有时很讨厌 但它们不是真正的虫或者身外之物 它们就存在于你的眼球中 因为“飞蚊”会不断地变形 所以人们会觉得它们是有生命的 其实不是 “飞蚊”是一种极小的物质,投影于视网膜 也就是眼球后部的光敏组织 它们可能是小块组织 红细胞 或是蛋白质团 由于它们悬浮于玻璃体 也就是眼内的胶状组织 “飞蚊”会随眼球而移动 眼球停止转动时 它又会少许地弹动 “飞蚊”大多数时候不易被察觉 当它们靠近视网膜时,它们变得可看见 这就相当于你把手放在吊灯下 更接近桌子时 手的阴影会更明显 “飞蚊”也会很明显 比如当你盯着发光的表面时 像是空白的屏幕 雪 或是晴空 因为颜色一致的背景会使“飞蚊”更明显 当看到的光越亮 瞳孔会收缩的更厉害 这就好比把许多散射的光 换成一个大的聚光灯 也会使得阴影更加明显 另外也有一种视觉现象与飞蚊症类似 但与之无关 当你仰望蓝天时 会看到小光点在快速闪动 这被称之为谢瑞尔氏现象 这与看到飞蚊相反 此时,你看到的不是阴影 而是一些移动的小开口让光进入视网膜 这些开口是由白细胞造成的 白细胞穿梭在视网膜表面的毛细血管 白细胞可以大到填满整个毛细血管 这导致了白细胞身前的空隙 由于这些空隙和白细胞本身 相比于血管中的红细胞 更能让蓝光透过 我们因此看到小光点 沿着毛细血管移动 也随着脉搏而移动 在理想状况下 甚至会看到光点后有条黑尾巴 这是白细胞身后堆积的红细胞造成的 有些科技馆中 会展览出一整屏幕的蓝光 这会让你跟清楚的看到这一现象 因为虽然每个人都会经历这些现象 每个人看到的程度都不同 就飞蚊症而言 大多数会被我们的大脑所忽视 但是数目异常多或者 大到影响视线的飞蚊 可能意味着你需要紧急医疗救助 但是多数的眼内现象 比如飞蚊或者谢瑞尔氏现象 只是委婉地提醒我们自认为看到的东西 取决于我们的生理和大脑 就和取决于外部世界一样