It may look like a tiny worm or a transparent blob.

它看起來可能像隻小蟲或透明團狀物。

And whenever you try to get a closer look, it disappears, only to reappear as soon as you shift your glance.

而每當你嘗試著近看時，它就會消失，在你移開目光後重新浮現。

But don't go rinsing out your eyes!

可別急著去洗眼睛啊！

What you are seeing is a common phenomenon known as a "floater".

你看到的是一個被稱為「浮游物」的普遍現象。

The scientific name for these objects is "muscae volitantes", Latin for "flying flies", and true to their name, they can be somewhat annoying.

這些東西的學名是「飛蠅幻視」，拉丁文直譯為「飛行的蒼蠅」，而正如其名，它們可能有點惱人。

But they're not actually bugs or any kind of external objects at all.

但它們其實完全不是蟲子或任何外在物品。

Rather, they exist inside your eyeball.

更準確地說，它們存在你的眼球之中。

Floaters may seem to be alive, since they move and change shape, but they are not alive.

浮游物看似活生生，畢竟它們會移動且變形，但它們不是活的。

Floaters are tiny objects that cast shadows on the retina, the light-sensitive tissue at the back of your eye.

浮游物是會在視網膜上投射陰影的微小物品，而是網模則是眼球後方的感光組織。

They might be bits of tissue, red blood cells, or clumps of protein.

它們可能是組織碎片、紅血球或蛋白質團。

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.

因爲它們懸浮在充斥眼球內部膠狀液體的玻璃體之中，浮游物會跟著你的眼球移動，在你眼球靜止時似乎稍微彈跳。

Floaters may be only barely distinguishable most of the time.

多數時候，浮游物可能幾乎無法被辨識出。

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.

它們距離是網膜越近，就會越明顯，就如同手掌越靠近上方懸掛頂燈的桌子時，會得到輪廓越清晰的影子。

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.

當你凝視如空白電腦螢幕、雪或是無雲天空等色調單一、明亮的表面時，浮游物現象尤為明顯，因為背景色彩的一致性使得它們更容易被辨別。

The brighter the light is, the more your pupil contracts.

燈光越亮，你的瞳孔收縮幅度越強。

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.

這種效果跟用單一頂燈泡替換大型擴散光燈具類似，會使得陰影顯得更清晰。

There is another visual phenomenon that looks similar to floaters, but is, in fact, unrelated.

還有另一個視覺現象跟懸浮物很類似，但它們其實毫無關係。

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".

如果你曾在凝視藍天時，看到微小光點飛來飛去，你就曾經歷過「藍天內視現象」。

In some ways, this is the opposite of seeing floaters.

就某些面向來說，這跟看到懸浮物完全相反。

Here, you are not seeing shadows, but little moving windows letting light through to your retina.

這時，你看到的不是陰影，而是讓光線觸及視網膜的小型移動式窗口。

The windows are actually caused by white blood cells moving through the capillaries along your retina's surface.

這些窗口其實是由在視網膜表面毛細管間移動的白血球引發。

These leukocytes can be so large that they nearly fill a capillary, causing a plasma space to open up in front of them.

這些白血球可能大到足以充滿一個毛細管，引起在它們前方出現血漿空間。

Because the space in the white blood cells are both more transparent to blue light than the red blood cells normally present in capillaries,

因為白血球空間之於藍光的透明度高於紅血球之於毛細管，

we see a moving dot of light wherever this happens, following the paths of your capillaries and moving in time with your pulse.

我們會在這個現象發生之處看到移動的點，遵循著毛細管線並與脈搏節奏同步。

Under ideal viewing conditions, you might even see what looks like a dark tail following the dot.

在理想視線環境下，你可能甚至會看到看似尾隨黑點的深色尾巴。

This is the red blood cells that have bunched up behind the leukocyte.

這是在白血球之後堆積的紅血球。

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.

有些科學博物館會展出包含藍光螢幕的展示品，讓你能夠比平常更清晰地看見這些藍天精靈。

While everybody's eyes experience these sort of effects, the number and type vary greatly.

雖然每個人的眼睛都會經歷此種效應，其數量與種類會有巨大差異。

In the case of floaters, they often go unnoticed as our brain learns to ignore them.

就浮游物的狀況，它們通常不會被發現，因為我們的頭腦已經習得要忽視它們。

However, abnormally numerous or large floaters that interfere with vision may be sign of a more serious condition, requiring immediate medical treatment.

然而，會干擾視線的異常大量或過大浮游物可能是較嚴重症狀的徵兆，需要立即就醫治療。

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.

但多數時候，像是浮游物或是藍天精靈等內視現象只是要稍微提醒我們，生理構造與思想對我們視覺認知的影響，與外部世界影響的程度相當。