It's at the DMV, it's at the optometrist,

是在車管所，是在驗光師那裡。

it's in doctor's offices all over the place.

它是在醫生的辦公室 所有的地方。

You probably know that font as the eye chart font.

你可能知道那個字體是眼圖字體。

And, you definitely know that huge E.

而且，你肯定知道那個巨大的E。

This thing is a dead simple tool for testing eyesight

這東西是測試視力的簡單工具。

and it's helped millions of people see better.

並幫助數百萬人看得更清楚。

- But, as simple as it is, there's some very precise math

- 但是，雖然簡單，但也有一些非常精確的數學知識

hidden away in those block letters.

藏在那些方塊字裡。

It doesn't just tell you if you need glasses,

它不只是告訴你是否需要眼鏡。

it tells you something about the fundamental limits

它告訴你一些關於基本限制

of human vision.

的人類視覺。

- And, we wanted to put that math to the test

- 而且，我們想把這個數學的測試。

on a slightly ridiculous scale.

在一個略顯荒謬的規模。

We've got the Coast Guard coming by.

海岸警衛隊來了。

Well, let's back up.

好吧，我們退後。

The eye chart we all know and love was created back

我們所熟知和喜愛的眼形圖，早在上世紀90年代就被創造出來了。

in 1862 by a Dutch ophthalmologist named Herman Snellen.

1862年，由一位名叫赫爾曼-斯奈倫的荷蘭眼科醫生。

His early prototypes used abstract shapes,

他的早期原型使用了抽象的形狀。

but he eventually settled on letters.

但他最終還是選擇了信。

And the designed hasn't changed much since then.

而且設計的也沒有什麼變化。

The chart is designed to measure one very particular aspect

該圖表的設計是為了衡量一個非常特殊的方面

of our eyesight, visual acuity,

我們的視力，視力。

or our ability to see very fine detail.

或者說我們能夠看到非常精細的細節。

It's basically the resolution of the eye.

基本上就是眼睛的分辨率。

Now here resolution isn't measured in pixels,

現在這裡的分辨率不是以像素來衡量的。

it's measured in degrees, like of an angle.

它是以度來衡量的，就像一個角度。

Which is weird, but here's why.

這很奇怪，但這是為什麼。

- [Rachel] Say you're looking at two lights shining

- 假設你看到的是兩盞燈在閃耀

at you from a distance, you can tell them apart

隔行如隔山，如隔靴搔癢

because the light from each source is traveling

因為每個源頭的光都在傳播

through your eye and hitting a different set

通過你的眼睛和打不同的一組

of light sensitive sells, called photoreceptors.

的光敏感賣點，稱為光感受器。

If you move the lights closer together,

如果你把燈移近一點。

they'll start hitting photoreceptors

他們會開始打擊光感受器。

that are closer to each other.

彼此比較接近的。

Especially because, as the light travels through the eye,

特別是因為，當光線穿過眼睛時。

it spreads out a little bit.

它分散了一點。

Eventually, the two lights will blend together

最終，這兩盞燈會融合在一起

and your brain will start to interpret them as one.

你的大腦會開始把它們解釋為一個整體。

That angle, between the two paths of light right

那個角度，在兩條光路之間的權利。

as you lose the ability to pick them apart,

因為你失去了把它們挑開的能力。

that's the resolution limit of your eye.

那是你眼睛的分辨率極限。

For healthy adults, it's on the scale

對於健康的成年人來說，它的規模

of just 1/60 of a degree, also known as one arcminute.

僅為1/60度，又稱1弧分。

- Snellen's eye chart is designed

- 斯奈倫的眼圖設計

with this resolution limit in mind.

考慮到這個分辨率的限制。

Take that little E in the middle.

就拿中間的那個小E來說吧。

It's built on a five by five grid,

它是建立在一個五乘五的網格上。

so that's the black lines and white spaces

黑線白格

are all the same width, about a 16th of an inch.

都是一樣的寬度，大約16英寸。

If you stand 20 feet away and look at that little E,

如果你站在20英尺外，看著那個小E。

each little black bar or space,

每個小黑條或空間。

is exactly one arcminute thick.

正好是一角分厚。

If you can read most of the letters in that row

如果你能讀懂這一行的大部分字母的話

at 20 feet away, you have 20/20 vision.

在20英尺外，你有20/20的視野。

Meaning, at 20 feet, the patterns of white and black

意思是說，在20英尺處，白色和黑色的花紋

are just at the limit of your eye's resolving power.

只是在你眼睛的解析力的極限。

Now, you might be able to read a row or two beneath 20/20,

現在，你也許能讀懂20/20下面的一兩行字。

most adults actually can.

大多數成年人其實都可以。

In fact, 20/20 was never defined as perfect or even average,

事實上，20/20從來沒有被定義為完美甚至是平均。

it's just a baseline to measure everything against.

它只是一個基線來衡量一切。

The row beneath that is the 20/15 line.

下面那一排是20/15線。

That means if you have 20/20 acuity,

也就是說，如果你有20/20的敏銳度。

you'd have to walk forward five feet to see it clearly.

你得往前走5英尺才能看清楚。

- All in all, with corrective lenses,

- 總而言之，帶著矯正鏡。

there isn't actually a huge range

其實範圍並不大

in acuity from one person to another.

在敏銳度上從一個人到另一個人。

Partly, because we have similar densities

部分原因是我們的密度相似

of photoreceptors in our eyes.

我們眼睛裡的光感受器的。

It's like we're all taking photos

好像我們都在拍照一樣。

with the same camera sensor.

具有相同的相機傳感器。

Compare that with other animals like eagles,

與老鷹等其他動物相比。

which have a very different optical setup than we do,

它有一個非常不同的光學設置與我們做。

including many more photoreceptors.

包括更多的光感受器。

Their eyes are camera sensors optimized

他們的眼睛是經過優化的相機傳感器

for spotting rabbits from midair.

用於從半空中發現兔子。

- Whatever your resolution limit is,

- 不管你的分辨率極限是多少。

you can use it to calculate your own acuity

你可以用它來計算你自己的敏銳度。

at different distances.

在不同的距離。

Based on the Snellen chart, Rachel's acuity

根據Snellen圖表，Rachel的敏銳度為：

is a bit better than 20/20, which makes

比20/20好一點，這就使得。

her maximum resolution just under one arcminute.

她的最大分辨率只有不到一弧分。

So, let's have a little fun with that.

所以，讓我們來玩一玩吧。

All we're gonna do is plant you in front

我們要做的就是把你安插在...

of this window right here, and we're gonna

這個窗口的權利在這裡，而我們要去

go out there and show you some very large E's,

去那裡給你看一些非常大的E的。

and all you have to do is tell us if you can identify the E.

而你要做的就是告訴我們，如果你能識別E。

We'll start small, that pier

我們從小事做起，那個碼頭

is about 1500 feet away from us.

距離我們大約1500英尺。

Since Rachel's acuity is a little better

因為Rachel的敏銳度更好一些

than one arcminute, she should comfortable see an E

比一弧分，她應該舒適地看到一個E。

if it's about 25 inches across.

如果它是大約25英寸寬。

Hello?

喂？

- [Rachel] Hi.

- [雷切爾]嗨。

- Hi, I'm going to show you an E,

- 嗨，我要給你看一個E。

and you tell me if it's facing the right way,

你告訴我它的方向是否正確。

if it's backwards.

如果是倒退。

- Okay.

- 好吧，我知道了

- [William] Okay, ready?

- [威廉]好了，準備好了嗎？

Which way is the E facing?

E朝哪邊？

- The open part of the E is facing towards the sky.

- E的開放部分是朝向天空的。

- [William] Perfect.

- [威廉]完美。

Now for the big finish.

現在是大結局。

Treasure Island out there in the bay,

金銀島在海灣裡。

is about two miles away, so to pull off the same eye exam,

是大約兩英里的距離，所以要拉開同樣的眼睛檢查。

we're gonna need a much bigger E, like 15 feet tall.

我們需要一個更大的E，像15英尺高。

Here we go, alright, gently, gently.

我們走吧，好吧，輕輕地，輕輕地。

Oh wind's catching it.

哦，風把它抓住了。

Did you see it?

你看到了嗎？

- I see an E, and it's pointed to the right.

- 我看到一個E，而且是指向右邊。

- [William] Tentative pointed to the right.

- [威廉]坦坦蕩蕩地指著右邊。

That is correct.

這是正確的。

- (laughs) The last thing to mention here

- (笑)這裡最後要提到的是

is that acuity is important but it's not the be all end all,

敏銳度是重要的，但它不是所有的一切。

your ability to sense movement, color, contrast,

你對運動、色彩、對比的感知能力。

depth, all of that factors into successful eyesight.

深度，所有這些因素都是成功的視力。

So acuity is just one tool of many

所以敏銳度只是眾多工具中的一種

to help you make sense of the world.

來幫助你理解這個世界。

- Now we've got the Coast Guard coming by.

- 現在，我們已經得到了海岸警衛隊的到來。

We are happy to be here testing the Coast Guard

我們很高興能在這裡測試海岸警衛隊。

on their visual acuity.

對他們的視力。

Okay, I think we're done.

好了，我想我們已經完成了。

Hey everyone, thank you so much for watching.

大家好，非常感謝大家的觀看。

This is part of the brand new Verge Science YouTube channel.

這是全新的Verge Science YouTube頻道的一部分。

We're putting a video out every week on this channel,

我們每週都會在這個頻道上放一段視頻。

so if this is the type of thing you're looking for,

所以如果你要找的是這種類型的東西。

hit the SUBSCRIBE button and come back every week.

點擊訂閱按鈕，每週回來。

And, let us know in the comments

而且，讓我們在評論中知道

what kind of thing you wanna see,

你想看到什麼樣的東西。

because we're gonna be doing a lot more.

因為我們會做得更多。