Our eyes allow us to visualize the world around us. They do this by converting light waves into neural signals so that our brains can process them.

眼睛赋予我们观察周围世界的能力。它能将光波转换为神经信号，以便大脑进行处理。

The eye itself is shaped like a sphere that is elongated horizontally, as opposed to being perfectly round, and only the anterior one-sixth of the eye is visible. The rest of the eye is contained within the orbit, or eye socket, of the skull.

眼球是一个水平径略长的球体，而非完美的球形。我们只能看到眼球的前1/6，其余部分位于头骨围成的眼眶中。

Now, the eye consists of three layers: the outermost fibrous layer, the middle vascular layer, and the inner neural layer. The outer fibrous layer contains two main structures: the sclera and the cornea.

眼球壁分为三层：最外层的纤维层，中间的血管层和内侧的神经层。外侧纤维层包括两个主要结构：巩膜和角膜。

The sclera makes up the majority of the outer layer and is the white portion of the eye. It’s like a tough, fibrous covering that protects the more delicate structures within the eye and it also acts as an anchoring point for the extrinsic eye muscles to attach to. The sclera is like a wall that’s built around the eye, that only has a tiny opening at the back to let the optic nerve through. As the sclera approaches the anterior portion of the eye it reaches a transition point known as the corneal limbus where it becomes the cornea.

巩膜是外层的主要组成部分，它呈乳白色，质地坚韧，保护眼内更微妙的结构，也是眼外肌附着点。巩膜像眼周围的一面墙，仅在后方有一个小孔让视神经通过。巩膜在眼前部经过角膜缘过渡点移行为角膜。

The cornea itself is a transparent, dome shaped clear layer that covers the iris and the pupil. It allows light to enter the eye, and its curved shape helps focus light on the retina in the back of the eye. At the periphery of the cornea, there are stratified squamous epithelial cells which continually divide and regenerate the cornea, and they help to heal after a corneal injury or abrasion.

角膜是一层略向前凸的透明偏横椭圆形结构，覆盖虹膜和瞳孔。它允许光线进入眼内，其曲面有助于光线聚焦在眼后的视网膜上。角膜上皮层是复层鳞状上皮，它们有分裂再生的能力，有助于促进角膜损伤后愈合。

The cornea doesn’t contain blood vessels and therefore immune cells can't access the cornea. As a result, it’s one of the few parts of the body that is considered "immune privileged" since it can be transplanted without the fear of an immune response and organ rejection.

角膜不含血管，因此免疫细胞无法到达角膜。角膜是机体少数“免疫赦免”的部位之一，因此角膜移植无需担心免疫反应和器官排斥。

Moving inwardly from the fibrous layer, the next layer of the eye is the middle vascular layer, which is also called the uvea. Structures within this layer include the iris, pupil, choroid, and ciliary body.

纤维层下是中间血管层，也称葡萄膜。它包括虹膜，瞳孔，脉络膜和睫状体。

The word "iris" derives from a Greek word meaning "rainbow", and that makes sense since the iris is what we think of as the colorful part of the eye. Eye color is determined by the amount of melanin in the iris. People with a high concentration of melanin have dark brown eyes, those with medium amounts have green eyes, and people with low concentrations of melanin have blue eyes.

“虹膜”一词源于希腊，意为“彩虹”，这有一定的道理，因为虹膜就是人们所见的眼睛颜色丰富的部分。眼的颜色由虹膜的黑色素含量决定。深棕色虹膜色素致密，绿色虹膜色素中等，蓝色虹膜色素较少。

The iris sits behind the cornea and it is composed of two distinct groups of muscle: the sphincter pupillae muscle, sometimes referred to as circular muscle, and the dilator pupillae muscle, otherwise known as radial muscle. These muscles help control the the size of the pupil, which is the central opening at the center of the iris.

虹膜位于角膜后，有两组不同的肌肉：瞳孔括约肌（也称环形肌）和瞳孔开大肌（也称辐射状肌）。它们共同参与调节瞳孔的大小（瞳孔是虹膜中央的圆孔）。

The sphincter pupillae muscle surround the iris like a tiny circle, and in bright light this muscle tightens around the pupillary opening, reducing the size of the pupil. When it’s dark, the dilator pupillae muscle pulls the iris radially or outwardly from the pupil which helps increase the diameter of pupillary opening, allowing more light to enter the eye.

瞳孔括约肌像一个小圆圈环绕虹膜，光线充足时，括约肌收缩使瞳孔缩小。光线较弱时，瞳孔开大肌收缩使瞳孔散大，使更多光线进入眼内。

After light passes through the cornea and pupillary opening of the iris, it reaches a biconvex transparent structure called the lens which is located in a space called the posterior chamber.

光线穿过角膜和瞳孔后，到达一个双凸透明状结构，称为晶状体（位于后房）。

Biconvex means that the lens is curved on both sides. The lens itself can bend, allowing it to become flatter or rounder, and this in turn bends the light entering the eye. A structure called the ciliary body, controls the degree to which the lens becomes flatter or rounder.

双凸面的意思是晶状体的前后都是曲面。晶状体富有弹性，可变得更平或更圆，能使进入眼内的光线发生折射。一个名为睫状体的结构调节晶状体曲度。

The ciliary body includes the ciliary muscle and tiny projections from the ciliary muscle called ciliary processes. The ciliary processes connect to suspensory ligaments which attach directly to the lens and hold the lens in place behind the iris as well as help it change shape. When the ciliary muscles relax the ciliary processes pull on the suspensory ligaments like a taut rope, and that makes the lens flatter.

睫状体包括睫状肌和睫状突（睫状肌的微小突起）。睫状突和悬韧带相连，悬韧带直接附着在晶状体上，将晶状体固定在虹膜后，并协助其变形。睫状肌松弛时，悬韧带紧绷，使晶状体变扁平。

Finally, the last structure of the vascular layer is a membrane called the choroid which is full of blood vessels that provide nutrients to most of the eye.

血管层的最后一个结构是一层膜，称为脉络膜，它的血管丰富，为大部分眼结构提供营养。

The choroid is dark brown in color, and that allows it to absorb light. Without the choroid, light would be more likely to reflect and scatter within the eye, preventing the light from being focused on the retina, which is necessary for visual processing.

脉络膜呈深棕色，可吸收光线。如果没有脉络膜，光线会在眼内反射和散射，无法聚焦在视网膜上（这是视觉处理必不可少的）。

The third and innermost layer of the eye is the retina.

眼球壁的第三层（最内层）是视网膜。

The retina has an inner neural layer that contains ganglion cells which synapse with bipolar cells, which then synapse with the photoreceptors - both rods and cones. The retina also has an outer pigmented layer consisting of a one cell-thick layer of pigmented epithelial cells.

视网膜的内神经层含有神经节细胞，它与双极细胞相连，后者再与光感受器（视杆细胞和视锥细胞）相连。视网膜外层色素层由单层的色素上皮细胞组成。

So when light enters the eyes, it hits the retina, then goes past the ganglion cells and bipolar cells to hit the rods and cones. The light that doesn’t hit the photoreceptors makes it to the pigmented layer where the light is absorbed so that it doesn’t scatter and bounce back to the photoreceptors.

光线进入眼内到达视网膜，穿过神经节细胞层和双极细胞层后刺激视杆及视锥细胞（感谢 @素颜麦粒肿 建议）。没有刺激光感受器的光线到达色素层后被吸收，这样就不会散射并反射回光感受器。

The rods are more numerous, about 120 million of them in each eye. Rods are highly sensitive to light and even a single photon can cause them to activate, making them great for seeing in low light conditions, but they only offer black and white vision.

视杆细胞数量更多，每只眼大约有1.2亿个。视杆细胞的光敏度高，甚至单个光子就能将其激活，这使得它们在弱光条件下有优势，但只有黑白视觉。

By comparison, there are only about 6 million cones in each eye, and most are located in the macula which is an oval spot in the middle of the posterior retina. At the center of the macula is the fovea which contains the highest concentration of cones and is the part of the retina that offers the highest visual acuity.

相比之下，每只眼只有大约600万个视锥细胞，且大多位于黄斑部（视网膜后极部的一个椭圆斑点）。黄斑中央处的中心凹（视锥细胞最密集处），是视网膜上视觉最敏锐的部位。

Cones are less sensitive than rods to light, and each cone can detect either a red, green, or blue wavelength of light. So when you see a red apple, only the red cones are activated, whereas when you see a purple flower, both the red and blue cones are activated.

视锥细胞的光敏度低于视杆细胞，每个视锥细胞仅能识别一种颜色的光波（红色、绿色或蓝色）。所以当人看到一个红苹果时，只有红色视锥细胞被激活，而当人看到一朵紫色花时，红色和蓝色视锥细胞都被激活了。

When rods and cones are activated, they hyperpolarize and create an action potential, which triggers depolarization of the bipolar cells, which then triggers the depolarization of the ganglion cells. The action potential in the ganglion cells travels through their axons to the posterior portion of the retina to form the optic nerve, which leaves the eye through the optic disc medial to the macula.

视杆和视锥细胞被激活，发生超极化并产生动作电位，从而刺激双极细胞去极化，后者再触发神经节细胞去极化。神经节细胞的动作电位沿轴突传递到达视网膜后，经过黄斑鼻侧的视乳头形成视神经。

The optic disc doesn’t have any photoreceptors so it’s known as the blind spot.

视盘无光感受器，所以被称为生理盲点。

The optic nerve then carries the visual information to the brain where we process and recognize the visual information.

视神经将视觉信息传到大脑进行识别和处理。

Finally, let’s zoom out and look at the eye as a whole. With a cross section of the eye, you can see that it’s split up into different chambers: The anterior chamber includes the area from the cornea to the iris, the posterior chamber is this really narrow space between the iris and the lens. And then this larger vitreous chamber includes the space between the lens and the back of the eye.

最后，让我们走出局部，把眼看作一个整体。在眼的横截面上，可看到它被分成不同的腔室：前房（角膜和虹膜之间的区域），后房（虹膜和晶状体之间的狭小空间），以及较大的玻璃体腔（晶状体和眼后壁之间的区域）。

Not to be too confusing, but both the anterior and posterior chambers are located in the anterior section of the eye, while the vitreous chamber is part of the posterior section of the eye.

但要注意，前房和后房均位于眼前节，而玻璃体腔属于眼后节。

Typically all of the chambers in the eye are filled with fluid. The chambers in the anterior section are filled with a liquid called aqueous humor, and the posterior section is filled with vitreous humor.

通常情况下，眼内所有腔室都充满液体。前房和后房由一种称为房水的液体充盈，玻璃体腔由玻璃体液充盈。

The aqueous humor is a transparent, watery fluid that is secreted by the ciliary epithelium, which in addition to secreting aqueous humor and providing nutrients to the lens and cornea, it provides structural support and helps to keep the shape of the eye. So that fluid’s secreted into the posterior chamber, and then flows through a narrow space between the front of the lens and the back of the iris through the pupil to the anterior chamber.

房水是由睫状体上皮分泌的一种透明水样液体，除了为晶状体和角膜提供营养外，还可以支持眼内结构，维持眼外形。房水进入后房，流经晶状体前部和虹膜后部之间的狭窄空间后，越过瞳孔进入前房。

From there the fluid flows out of the eye through the trabecular meshwork, which is a spongy tissue that acts like a drain, and this allows the fluid to go down into a circular channel called the canal of Schlemm and finally into aqueous veins that are part of the episcleral venous system—the veins around the sclera of the eye.

再从前房的小梁网（海绵状排泄通道）进入Schlemm管，最后进入房水静脉（巩膜表面的静脉系统的一部分）。

Alright, as a quick recap…..the wall of the eye is made up of three major layers, the fibrous outer layer which contains the cornea and sclera, the middle vascular layer consisting of the iris, pupil, choroid and ciliary body, and finally the neural layer consisting of the retina with its own outer pigmented layer and inner neural layer.

好的，快速回顾一下。眼球壁分为三层：外层纤维膜（包括角膜和巩膜）；中间血管层（包括虹膜,瞳孔,脉络膜和睫状体）；内层视网膜（包括外色素层和内神经层）。

The inner neural layer of the retina is composed of photoreceptor cells that finally convert light into neural signals that travel via the optic nerve to the brain for visual processing.

视网膜的内神经层由感光细胞组成，负责把光转化为神经信号，经视神经传到大脑进行视觉处理。

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