One of the most important parts of the eye isn't a structure at all — it's an open space. It's the pupil of the eye.
瞳孔是眼睛最重要的部分之一，它不是一个结构，而是一个开放的空间。
Pupil Definition
The pupil is the opening in the center of the iris (the structure that gives our eyes their color). The function of the pupil is to allow light to enter the eye so it can be focused on the retina to begin the process of sight.
Typically, the pupils appear perfectly round, equal in size and black in color. The black color is because light that passes through the pupil is absorbed by the retina and is not reflected back (in normal lighting).
If the pupil has a cloudy or pale color, typically this is because the lens of the eye (which is located directly behind the pupil) has become opaque due to the formation of a cataract. When the cloudy lens is replaced by a clear intraocular lens (IOL) during cataract surgery, the normal black appearance of the pupil is restored.
There's another common situation when the pupil of the eye changes color — when someone takes your photo using the camera's flash function. Depending on your direction of gaze when the photo is taken, your pupils might appear bright red. This is due to the intense light from the flash being reflected by the red color of the retina. [red eyes in photos]
瞳孔的定义
瞳孔是虹膜(赋予眼睛颜色的结构)中心的开口。瞳孔的功能是让光线进入眼睛，然后聚焦在视网膜上，开始视觉过程。
一般来说，瞳孔呈完美的圆形，大小相等，呈黑色。黑色是因为通过瞳孔的光线被视网膜吸收而没有反射回来(在正常光线下)。
如果瞳孔混浊或苍白，通常是因为眼睛晶状体(位于瞳孔正后方)由于白内障的形成而变得不透明。在白内障手术中，当混浊的晶状体被透明的人工晶状体(IOL)取代时，瞳孔正常的黑色外观就会恢复。
瞳孔变色还有另一种常见情况——当有人用相机的闪光功能给您拍照时，根据拍照时凝视的方向，您的瞳孔可能会显示鲜红色，这是由于来自闪光灯的强光反射了视网膜的红色。[照片中的红眼]
Pupil Function
Together, the iris and pupil control how much light enters the eye. Using the analogy of a camera, the pupil is the aperture of the eye and the iris is the diaphragm that controls the size of the aperture.
The size of the pupil is controlled by muscles within the iris — one muscle constricts the pupil opening (makes it smaller), and another iris muscle dilates the pupil (makes it larger). This dynamic process of muscle action within the iris controls how much light enters the eye through the pupil.
In low-light conditions, the pupil dilates so more light can reach the retina to improve night vision. In bright conditions, the pupil constricts to limit how much light enters the eye (too much light can cause glare and discomfort, and it may even damage the lens and retina).
瞳孔功能
虹膜和瞳孔共同控制进入眼睛的光线。就像照相机一样，瞳孔是眼睛的光圈，虹膜是控制光圈大小的隔板。
瞳孔的大小是由虹膜内的肌肉控制的——一块肌肉收缩瞳孔(使其变小)，另一块虹膜肌肉扩张瞳孔(使其变大)。虹膜内肌肉运动的动态过程控制着通过瞳孔进入眼睛的光线。
在弱光条件下，瞳孔会扩张，这样更多的光线就能到达视网膜，从而改善夜间视力。在明亮的环境下，瞳孔会收缩以限制进入眼睛的光线(过多的光线会导致眩光和不适，甚至会损害晶状体和视网膜)。
Pupil Size
The size of the pupil varies from person to person. Some people have large pupils, and some people have small pupils. Also, pupil size changes with age — children and young adults tend to have large pupils, and seniors usually have small pupils.
Generally, normal pupil size in adults ranges from 2 to 4 millimeters (mm) in diameter in bright light to 4 to 8 mm in the dark.
In addition to being affected by light, both pupils normally constrict when you focus on a near object. This is called the accommodative pupillary response.
瞳孔的大小
瞳孔的大小因人而异。有些人瞳孔大，有些人瞳孔小。此外，瞳孔大小随年龄变化——儿童和年轻人的瞳孔往往较大，老年人的瞳孔通常较小。
一般来说，成年人正常的瞳孔大小在明亮光线下为2至4毫米，在黑暗中为4至8毫米。
除了受到光线的影响外，当您聚焦在近的物体上时，两个瞳孔通常都会收缩。这称为瞳孔调节反应。
瞳孔，是眼睛内虹膜虹膜中心的小圆孔，为光线进入眼睛的通道，瞳孔的直径对人眼的像差有着重要的影响。虹膜上平滑肌的伸缩，可以使瞳孔的口径缩小或放大，控制进入瞳孔的光量。一般瞳孔直径2.5~5.0mm，明亮环境中瞳孔缩小，约2.0~4.0mm，进入眼内光量减少，离轴光线减少，导致像差减少、视觉质量提高、景深增加，视物清晰、舒适。黑暗环境中瞳孔扩大，约4.0~8.0mm，进入眼内光量增多，离轴光线增多，导致像差增大、视觉质量降低、景深减小，星芒和眩光增多，视觉不适症状增加。
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