your field of vision becomes slightly smaller,

你的視野一天比一天小

narrowing or dimming

越來越狹窄或模糊

until eventually you go completely blind.

直到你完全看不見

We tend to think of blindness as something you're born with,

我們總是認為失明是天生的

but in fact, with many diseases like Retinitis pigmentosa

事實上很多疾病像是 色素性視網膜炎

and Usher syndrome,

和尤塞氏綜合症等疾病

blindness can start developing when you're a kid,

視力會從小開始退化

or even when you're an adult.

或甚至在成人期開始

Both of these rare genetic diseases affect the retina,

二種少數的遺傳疾病會影響視網膜

the screen at the back of the eye that detects light and helps us see.

視網膜在眼睛後方 用來感受光線形成視覺

Now imagine if the eye could regenerate itself

想像一下眼睛若能自動復原

so that a blind person could see again.

那麼盲人就能重見光明了

To understand if that's possible, we need to grasp how the retina works

要了解其可行性 要先窺探視網膜的運作

and what it has to do with a multitalented creature

和多樣化生物斑馬魚又有何關聯

named the zebrafish.

人類的視網膜由不同細胞層組成

The human retina is made of different layers of cells,

在眼睛後方有特殊的神經細胞

with special neurons that live in the back of the eye

為視桿及視錐的感光細胞

called rod and cone photoreceptors.

感光細胞將吸收的光線轉換成

Photoreceptors convert the light coming into your eye

大腦訊號並形成影像

into signals that the brain uses to generate vision.

尤塞氏綜合症和 色素性視網膜炎的患者

People who have Usher syndrome and retinitis pigmentosa

感光細胞會逐步退化

experience a steady loss of these photoreceptors

最後視網膜無法偵測光線

until finally that screen in the eye can no longer detect light

也不能傳遞訊號到大腦

nor broadcast signals to the brain.

不像大多的身體細胞一樣

Unlike most of your body's cells, photoreceptors don't divide and multiply.

感光細胞無法分裂和複製

We're born with all the photoreceptors we'll ever have,

人的感光細胞數量始終如一

which is why babies have such big eyes for their faces

這是為什麼寶寶的眼睛看起來較大

and part of why they're so cute.

也是他們這麼可愛的原因

But that isn't the case for all animals.

但不是所有的動物都是如此

Take the zebrafish, a master regenerator.

以再生專家斑馬魚為例

It can grow back its skin, bones, heart and retina after they've been damaged.

魚皮、魚骨、心臟和 視網膜在受損後都能再生

If photoreceptors in the zebrafish retina are removed or killed by toxins,

如果其視網膜的感光細胞 因有害物質而消失

they just regenerate and rewire themselves to the brain to restore sight.

只要自行再生感光細胞就能回復視力

Scientists have been investigating this superpower

科學家一直在研究其超能力

because zebrafish retina are also structured very much like human retina.

因斑馬魚和人的視網膜結構非常相似

Scientists can even mimic the effects of disorders like Usher syndrome

科學家甚至能在斑馬魚的眼睛模擬 尤塞氏綜合症

or retinitis pigmentosa on the zebrafish eye.

或色素性視網膜炎等病症

This allows them to see how zebrafish go about repairing their retinas

這能讓他們研究 斑馬魚如何修復感光細胞

so they might use similar tactics to fix human eyes one day, too.

或許某天人類的視力 也能用類似的方式復原

So what's behind the zebrafish's superpower?

那斑馬魚超能力的秘密是什麼？

The main players are sets of long cells that stretch across the retina

主要機制在於 視網膜內的放射狀細胞

called Müller glia.

名為米勒神經膠質細胞

When the photoreceptors are damaged, these cells transform,

當感光細胞受損時 此細胞會產生變化

taking on a new character.

去執行新任務

They become less like Müller cells and more like stem cells,

米勒神經膠質細胞會變得像幹細胞

which can turn into any kind of cell.

可分化成任何細胞

Then these long cells divide,

這些放射狀細胞能分裂

producing extras that will eventually grow into new photoreceptors,

製造新細胞 進而生成新的感光細胞

travel to the back of the eye and rewire themselves into the brain.

重回視網膜並重新連結大腦

And now some researchers even think they've found the key to how this works

有些研究員甚至認為 已找到其運作的關鍵

with the help of one of two chemicals that create activity in the brain

在於促進大腦活化其中二種化學物質

called glutamate and aminoadipate.

為麩胺酸和氨基乙二酸

In mouse eyes,

在老鼠的眼睛裡

these make the Müller glia divide and transform into photoreceptors,

這讓米勒神經膠質細胞 分裂並分化為感光細胞

which then travel to the back of the retina,

接著重回視網膜後方

like they're replenishing a failing army with new soldiers.

有如老弱殘兵的軍隊加入了生力軍

But remember, none of this has happened in our retinas yet,

請記得這些都未發生在我們的視網膜

so the question is how do we trigger this transformation of the Müller glia

問題在於我們要如何讓 米勒神經膠質細胞

in the human eye?

在人類眼睛裡分化?

How can we fully control this process?

我們要如何完全掌控這個過程

How do photoreceptors rewire themselves into the retina?

要怎麼讓感光細胞和 視網膜再連接在一起

And is it even possible to trigger this in humans?

能不能適用於人類？

Or has this mechanism been lost over time in evolution?

或是這機制已隨演化消失

Until we tease apart the origins of this ability,

在我們釐清來龍去脈前

retinal regeneration will remain a mysterious superpower

視網膜再生會一直是斑馬魚的

of the common zebrafish.

神秘超能力