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视力那些事

Why Don't Other Animals Wear Glasses?

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这一集由The Great Courses Plus支持
This episode is supported by The Great Courses Plus
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我从来没有看过戴眼镜的大猩猩 戴隐形眼镜的变色龙或是
I’ve never seen a gorilla with glasses, a chameleon with contacts, or a moose with
带单片眼镜的驼鹿 尽管我曾见过一只戴眼镜的熊
a monocle. Although I did see a spectacled bear once.
但是就和70%的美国人一样 我的眼睛不能很好地聚光 所以
But like 7 out of 10 Americans, my eyes don’t bend light correctly, so I’ve worn glasses
我自从五年级就戴了眼镜这是一个让人困惑的问题:
since fifth grade. It’s a confusing question: How did our species
如果我们中的许多人看不见 人类要如何在自然选择的考验中生存下来呢
survive the trials of natural selection if so many of us can’t see?
我们不能带水獭或是鸵鸟去看眼科医师所以要弄清楚
We can’t take otters or ostriches to the ophthalmologist, so it’s hard to know exactly how
视力低下在动物王国到底有多普遍是很困难的
common bad eyesight is in the animal kingdom.
但是如果你能闻 听或是感受你的生活那好视力就是可有可无的
But if you can smell, hear, or feel your way through life, good eyes are expendable.
很多依赖视觉的物种 牺牲了能够看得十分清晰的能力
Many species that rely on seeing sacrifice clear vision all over
来获得自然选择要求的快速识别能力
to see extra-sharp where natural selection demands.
对许多有视力的物种来说 在你传递未进化完全的基因前 你更可能成为猎物
For most visual species, you’re more likely to become a meal before you pass on your blurry
所以它们在种群中消失了
genes, so they vanish from the population.
但是现代人类过着十分舒适的生活 所以自然选择
But modern humans live a pretty comfortable life, so natural selection has let us
允许我们带着糟糕的视力蒙混过关
slip through with bad eyesight.
你眼睛里的晶状体不是坚硬的 它更像是商店里的果冻 它由一种叫做
The lens inside your eye isn’t rigid—more like really firm Jell-O. It’s made from
晶状体蛋白的柔韧的蛋白质构成
flexible proteins called crystallin.
它们让可见波长通过 但是晶状体圆形的形状会使光线弯曲
They let visible wavelengths pass through, but the lens’s rounded shape bends the light.
折射:就像是水与空气交界处出现的现象
Refraction: just like what happens where air meets water.
我们不能像使用相机那样控制晶状体距离视网膜的远近
We can’t focus by moving our lens closer or farther from the retina, the way a camera
我们实际上是通过压缩和拉伸晶状体来改变它折射光线的程度
would. We actually squish and pull our lens to change how it bends light.
现在 物体能反射各个方向的光
Now, objects reflect light in all directions.
物体越远 光线进入
The farther away an object is, the angles between
我们眼睛时的角度就越小 因而我们的晶状体不需要大幅度弯曲
the light rays entering our eyes are smaller, and our lens doesn’t need to bend them
正因如此 睫状肌能得到放松
as much, so tiny muscles relax and flatten it.
物体移动得越近 光线
As an object moves closer, light rays are
就会以更大的角度通过晶状体 因而睫状肌把晶状体压缩得更圆
hitting our lens at wider angles, so muscles squeeze the lens into a rounder shape to bring
来使焦点能准确地位于视网膜上
the focal point right onto the retina.
我们会情不自禁地这样 健康的眼睛能够在半秒内从无限远到近处
We do all this involuntarily—healthy eyes can focus from infinity to here in less than
聚焦
half a second.
但是对于大部分人来说 这个过程不会很顺利
But in many of us, this process doesn’t work perfectly.
有近视的人
People with myopia, or nearsightedness,
看远处的物体有困难 通常这是因为眼球太长就像橄榄球那样
have trouble focusing on objects far away, often because the eye is too long—kind of football-shaped.
这样的晶状体聚光时 会使影像成于视网膜前 如果你有散光
The lens focuses the image in front of the retina. Or if you have astigmatism,
和我一样 你的角膜太圆 会产生奇怪的模糊效果
like me, your cornea is too round, producing weird blurry effects.
这可以用凹透镜矫正 它能够在光进入眼睛之前 先分散一点点
This is corrected by using a lens that spreads the light out just a tiny bit before it enters the eye.
现在焦点刚好落在视网膜上了
The focal point now hits right on the retina.
如果眼球太短或是晶状体不能压缩到足够圆的程度
If the eye is too short or the lens can’t quite squish into a round enough shape,
当试着看近物时 焦点就会移动到视网膜之后
the focal point moves behind the retina when trying to view things up close.
我们把这种情况称为远视
We call this hyperopia, or farsightedness.
凸透镜能在光线进入眼睛前 稍微聚集
And it’s corrected using a lens that slightly focuses the light in
就像戴着小型放大镜 可以矫正远视眼
front of your eye—kind of like wearing tiny magnifying glasses.
当我们年老时 人们经常会有老花眼:我们的晶状体会失去弹性
As we age, people often get presbyopia: our lens becomes less elastic, unable to squish
不能压缩到足以看清近物的程度
enough to bring the closest objects into focus.
如果有人已经要求矫正视力
If somebody already requires distance correction,
他们通常会配有双光眼镜或是戴两种不同的眼镜:
often they’ll be be fitted with bifocals or contacts with two different types of lenses:
一个远视眼镜 一个近视眼镜
one for far and one for near.
隐形眼镜能像边框眼镜一样矫正视力
Contact lenses correct these problems the same way as glasses do—you just don’t notice
你不需要留心不同镜片在你指尖的形状
the different lens shapes on the tip of your finger.
像LASIK这样的矫正手术事实上不会改变你的晶状体
Corrective surgeries like LASIK don’t actually work on your lens.
它会使用激光来改造前面的圆形角膜
They use lasers to reshape the round cornea in front of it,
使它调整到能自然聚光的程度
adjusting how it naturally bends light.
奇怪的是 在过去半个多世纪里 发达国家的人们视力变得越来越差
Strangely, over the past half century, eyesight is getting worse in developed countries.
60年前 10%的中国人患有近视 但是现在有90%的年轻一代患有近视
60 years ago, nearsightedness affected 1 in 10 Chinese people, but today it affects 90% of
单韩国首尔 就有97%的19岁男性需要戴眼镜
the younger generation. In Seoul, Korea alone, 97% of 19-year-old males need corrective lenses.
这种变化太快 不能无法单纯地归咎于基因 通常认为
The change is too fast to be due to just genetics. It was originally thought that the culprit
这要归咎于长时间近距离地看电子设备 但是最新研究表明
was too much time spent reading or staring at devices up close, but newer research suggests
最大的风险在于孩子们在室外阳光下呆的时间太短
that the biggest risk factor could be kids spending less time outside under bright sunlight.
所以我们的视力能变得有多好呢?我们能看得像鹰那样清楚吗?
So how good can our vision get? Could we see like eagles?
眼睛的晶状体不论是天生的还是人造的 只要状况良好
When our lenses—natural or prosthetic—are just right,
人类视力的极限就能高于20/20 事实上更接近20/8
the limit of human vision is lower than 20/20—actually closer to 20/8.
在视觉反射运动领域的专业运动员 例如排球运动员通常在这个范围内
Professional athletes in visual reflex sports like baseball are often down in this range.
我们视力的极限并不来自于把事物集中在焦点上
The limit to our vision doesn’t come from being able to bring things into focus;
因为在我们视网膜上的视锥细胞只是挤在一起
it’s because the cone cells on our retina are only packed so close together.
就像相机传感器上的像素点 我们不能描述比单细胞更小的东西
Like pixels on a camera sensor, we can’t pick up detail smaller than a single cell.
像鹰一样的猛禽 它们的视网膜上有更紧密的细胞
Birds of prey like hawks have more tightly packed cells on their retinas,
所以它们可以比人类看到更多的细节
so they can see more detail than we can.
很奇怪的是 那些脱去自然虹膜的人可以看到更宽的波长
What’s strange is people who have had their natural lenses removed can see expanded wavelengths,
甚至能达得到紫外线的波长范围艺术家克劳德•莫奈属于这一类人
down into the ultraviolet range. Claude Monet, the artist, was one of these people.
我们为他做了一个视频 你可以点击这里
We made a video about him; you should check it out.
也许我们从没见过超人 但是感谢物理 让我们的眼睛可以聚焦
We might not ever see like Superman, but thanks to physics, we can bring our vision into focus.
保持好奇
Stay curious.
感谢The Great Courses Plus对本集的支持
Thanks to The Great Courses Plus for sponsoring this episode.
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让我们假设你想知道你的视力发生了什么变化
Let’s say you wanna know what happens to your vision after your eye—
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不像大部分的病毒 寨卡病毒不但
Unlike most viruses, not only can Zika cross
能通过母亲的胎盘传给婴儿
the placenta from mother to child—
而且现在我们知道它的具体目标在于
but we now know it specifically targets
脑细胞
developing brain cells.
更糟糕的是 寨卡病毒也会杀死反射状胶质细胞
Worse, Zika also kills radial glial cells,
它经常充当支架
which normally act as a scaffold
来塑造发育中的大脑
to shape the developing brain.
没有治疗方案或是疫苗 并且症状
There’s no treatment or vaccine, and symptoms
通常很不明显导致很多人
are usually so mild that most people
甚至没有意识到他们患病
don’t even know they have it
世界卫生组织只能去寨卡病毒肆虐的地方告诉当地女性
The World Health Organization has resorted to telling women in Zika-affected areas,
“不要怀孕”——这是一个很好的迹象 我们别无选择
“don’t get pregnant”—which is a pretty good sign we don’t have any good options.

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