人眼

The reason people can see words on paper, the sunrise in the morning, or the bright light of the moon at night, it is because of the human eyes. A person can view some of the parts of the human eye by looking into a mirror.

人们之所以可以看到纸上的字、早晨的日出或是夜晚明亮的月光都是因为人的眼睛。我们可以在照镜子的时候观察到眼睛的一部分。

The eye is situated inside a hollow area of the skull called the eye socket. The eyelid protects the front part of the eye keeping it clean and moist by blinking. This is the opening and shutting of the eye throughout the day. Blinking is both voluntary, meaning it can be controlled, and involuntary, meaning it sometimes happens automatically. When the eyelid blinks automatically, it is a reflex. This reflex occurs when the eyes need to adjust to bright light, or when they are needed to shut quickly for protection. The eyelids keep dirt and other substances from entering a person's eyes.

眼睛位于眼窝头骨的中空区域内。眼睑保护眼睛的前部，通过眨眼使其保持清洁和湿润。这也控制了眼睛全天的开合。眨眼可以是可控制的，也就是说它也可以通过人为控制非自愿地进行也可以在不知情的情况下自动发生。自然情况下的眨眼是一种条件反射。当眼睛需要调整到更为明亮的光线，或在为了保护眼睛而需要迅速闭眼时就会出现此反射。眼睑防止污垢和其他物质进入人的眼睛。

The white part of the eye is the sclera. The sclera is the outer covering of the eyeball, which is made of a very tough material. It also contains blood vessels that deliver blood to the sclera. The cornea is a transparent dome that is located in front of the colored part of your eye. It helps with the focusing of the eye when light enters. It is a very difficult part to see because it is made of a clear tissue. Think of the cornea as a window the person's eye sees through.

眼睛的白色部分是巩膜。巩膜是眼球，它由非常坚硬的材料组成。该部分也包括了向巩膜输送血液的血管。角膜是位于眼睛的彩色部分前的透明圆顶。它有助于眼睛对光聚焦。这是一个非常难观察到的部分因为它的是由透明组织组成。可以把角膜看作人眼的一扇窗户。

Located behind the cornea is the iris, which is the colorful part of the eye.  There are muscles attached to the iris that change its shape, which controls the amount of light going through the pupil. The pupil is the black circle in the middle of the iris and lets the light enter the eye. The pupils adjust to the light by opening wider when more light is needed, and shrinks when there is plenty of light available. The anterior chamber is the space between the iris and cornea, which is filled with a transparent fluid keeping the eye healthy.

位于角膜后面的是虹膜，这是眼睛色彩丰富的一部分。与虹膜相连的肌肉改变其形状从而控制进入瞳孔的光的量。瞳孔是虹膜中间的黑色圆圈，光线通过瞳孔进入眼内。瞳孔可以收缩，当需要更多的光线时，瞳孔扩张；当周围的光线十分充足，瞳孔紧缩。眼球前房在虹膜和角膜之间，前方中充满透明流体用来保护眼睛的健康。

When light enters the eye it next hits the lens, which is located behind the iris and it is transparent. Like all lenses, they are usually used to focus light, and this is what the lens of the eye does. It focuses light rays on the back of the eyeball to the retina. This part is home to millions of cells that are sensitive to light. The retina takes the light and changes it to signals which are sent to the brain. The brain in turn is able to tell a person what they are seeing. The image received in the eye is actually upside down when the optic nerve, like a high speed telephone line, sends the signal to the brain, When the brain receives it, though, the image seen is flipped right-side up. This happens so fast; a person won't even realize what is happening between the eyes and brain.

光进入眼睛后照在虹膜后面的透明的晶状体上。如同所有的透镜，晶状体也用于将光聚焦。它将光线聚焦到眼球后部的视网膜上。这部分由数百万光敏细胞组成。视网膜接收光线，并将其转换成发送到大脑的视觉信号。而大脑则告诉人眼所看到的画面。眼睛接收到的图像实际上是颠倒的，视神经像高速电话线将信号发送到大脑，当大脑接收到它所看到的图像被向右朝上翻。这个过程发生的太快以致人无法意识到眼睛到大脑之间发生的这一系列活动。

There is also a muscle located in the eye called the ciliary muscle. This muscle changes the shape of the lens when things are needed to be seen up close, far away, or out of the corners of the eyes. The lens becomes thicker when a person needs to see something up close, like reading, but becomes thinner when seeing something far away, like when riding a bike. The largest eye part is the vitreous body, which takes up about 2/3 of the volume of the eye, as well as giving the eye its shape.

眼睛附近也有一种被称为睫状肌的肌肉。当人需要看清远近距离不同的物体，则需要睫状肌调整晶状体形状。当人需要看清近在眼前的物体，比如阅读，晶状体就会变厚；而当人需要看清远处的东西，比如骑自行车时，晶状体就会变得很薄。眼睛最大的部分是玻璃体，约占据了眼睛的容积的2/3，而且玻璃体也决定了眼睛的形状。

The retina also uses special cells called rods (about 120 million of them) and cones (7 million) located in each eye to help it process light. The rods see in black, white and gray and passes along the shape of what is seen. It also can tell the difference between colors, and helps a person's vision when there is very little light. Cones are more helpful in bright light.

视网膜上有特殊的视杆细胞，每只眼睛上约有1.2亿个视杆细胞和7亿个视锥细胞用于处理光线。视杆接收黑色、白色和灰色光线并且传递所看到物体的形状。视杆细胞还可以区分颜色，并用于夜视力。而视锥细胞在光线明亮时发挥的作用更大。

In summary, there are many parts of the eyes that work together to help you see and enjoy the different sights and colors surrounding you throughout the day.

总之，无数眼睛内的组织协同作用使得人类看到和欣赏不同的风景以及周边的五光十色。