Your eyes pick up color using a type of cell called cones in your retina. The same is true for dogs， though our cones aren’t exactly the same.

“Humans have three types of cones， which enables us to see different shades of red， blue-violet， and green，” says Alison Meindl， a professor at Colorado State University.

“Dogs have two types of cones that pick up blue-violet and yellow shades，” says Lara Sypniewski， a professor of small animal medicine at Oklahoma State University.

This means that dogs see in a similar way to humans who are red-green colorblind. “They don’t see red or green and they see everything in shades of blue and yellow，” says Jay Neitz， PhD， a professor of ophthalmology at the University of Washington.

Humans may have the advantage in color vision， but dogs definitely have us beat in the realm of night vision. “This is because dogs’ eyes have more light-gathering power than ours，” Neitz says.

“A dog’s retina is largely composed of cells called rods， which can sense light， even in very low-light conditions，” says Sypniewski.

人類的眼睛通過(guò)視網(wǎng)膜的視錐細(xì)胞感知顏色，狗也是如此，但兩者的視錐細(xì)胞并不完全相同。

美國(guó)科羅拉多州立大學(xué)教授艾莉森·梅恩德稱：“人類有三種視錐細(xì)胞，因此我們能夠看到不同深淺的紅色、藍(lán)紫色和綠色?！?/p>

美國(guó)俄克拉荷馬州立大學(xué)小型動(dòng)物醫(yī)學(xué)教授拉臘·西普尼夫斯基稱：“狗有兩種視錐細(xì)胞，可以分辨藍(lán)紫色和黃色。”

這意味著狗的視覺與紅綠色盲的人相似。華盛頓大學(xué)眼科教授杰伊·內(nèi)茨博士稱：“狗看不見紅色和綠色，但能看到藍(lán)色和黃色。”

人類在色覺方面可能有優(yōu)勢(shì)，但狗的夜視能力肯定比人類強(qiáng)。內(nèi)茨說(shuō)：“這是因?yàn)楣返难劬Ρ热说难劬Ω酃??！?/p>

西普尼夫斯基說(shuō)：“狗的視網(wǎng)膜主要由視桿細(xì)胞組成，即使在光線很弱的情況下，視桿細(xì)胞也能感知光線。”

Dogs are especially good at sensing movement. “The increased number of rods in the dogs’ retina also increases their ability to detect motion，” Sypniewski says. This ability can help them detect small prey like squirrels.

Dogs have a wider field of vision than humans. Dogs’ eyes are set slightly farther apart than humans’ eyes， so they can see further to the side in each direction.

Dogs have blurrier long-distance vision than humans. A human with perfect vision has 20/20 vision， while dogs have 20/65 to 20/85. “This means that a dog must be at 20 ft to read a letter that a human with 20/20 vision would be able to read at 65 or 85 ft，” says Sypniewski.

Dogs have trouble seeing things very close up. Dogs can see objects clearly if they’re at least 13 to 20 inches away from their eyes， but if the object is closer， the image may be blurry. Humans can see objects slightly closer—about 10 inches away from the eye.

Dogs may recognize you by your shape and motion. “If your dog recognizes you from a distance， it is not because it can see the details of your face like a human would， but rather because of your shape or the way you move，” Neitz says.

狗特別擅長(zhǎng)感知運(yùn)動(dòng)。西普尼夫斯基說(shuō)：“狗的視網(wǎng)膜中視桿細(xì)胞數(shù)量多，這使得它們觀察運(yùn)動(dòng)的能力更強(qiáng)?！边@種能力可以幫助它們發(fā)現(xiàn)像松鼠這類小獵物。

狗的視野比人類更寬。狗的眼間距比人的稍遠(yuǎn)，因此狗能看到的兩側(cè)范圍更廣。

狗的遠(yuǎn)距離視力比人類更模糊。擁有完美視力的人類有20/20的視力，而狗有20/65至20/85的視力?！斑@意味著一個(gè)擁有20/20視力的人在65或85英尺（約20或26米）處能看到的字，狗必須在20英尺（約6米）處才能看見?！蔽髌漳岱蛩够f(shuō)道。

狗看不清離自己很近的事物。當(dāng)物體距離眼睛至少13到20英寸（約0.3到0.5米）遠(yuǎn)時(shí)，狗才能看清楚，但如果物體更近，眼中的圖像可能就會(huì)模糊不清。人類可以看到更近的物體——大約10英寸（約0.25米）遠(yuǎn)。

狗可以通過(guò)人的身形和動(dòng)作識(shí)別主人。內(nèi)茨說(shuō)：“如果你的狗能從遠(yuǎn)處認(rèn)出你，那不是因?yàn)樗芟袢祟愐粯涌辞宄愕哪槪且驗(yàn)檎J(rèn)出了你的身形或走路的方式?！?/p>

Word Bank

retina /'ret?n?/ （復(fù)數(shù)retinas/retinae） n. 視網(wǎng)膜

realm /relm/ n. 領(lǐng)域；場(chǎng)所

prey /pre?/ n. 獵物

The lion will often watch over its prey for hours.

blurry /'bl??ri/ （blurrier為其比較級(jí)） adj.? 模糊不清的