Bilingual edition: English is preserved and Chinese follows each unit. Terminology uses the confirmed v20260916 glossary; automated semantic review remains traceable.
中英双语版：英文原文完整保留，中文紧随对应单元；术语采用 v20260916 确认表，自动语义审校结果可追溯。
Design parameters
设计参数
 Accommodation model
适应模型
 Index

Vision concepts

Image formation concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 图像形成概念 参考 Hecht，第2版 第5.7节
 
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The Cornea

角膜

The cornea represents the strongest part of the refracting power of the eye, providing about 80% of the power of the system. The index of refraction of the cornea is about 1.376. Rays pass from the cornea into the watery fluid known as the aqueous humor which has an index of refraction of about 1.336, so most of the refraction is at the cornea-air interface.

角膜是眼睛折射力最强的部分，提供了系统折射力的约80%。角膜的折射率约为1.376。光线从角膜进入称为房水的流体，其折射率约为1.336，因此大部分折射发生在角膜-空气界面。
 Index

Vision concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 参考 Hecht，第二版 第5.7节
 
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Crystalline Lens

晶体透镜

About 9mm in diameter and 4 mm thick, the crystalline lens provides perhaps 20% of the refracting power of the eye. Hecht likens it to a tiny transparent onion with some 22,000 fine layers. The index ranges from about 1.406 at the center to about 1.386 in outer layers, making it a gradient index lens. It is pliable, and changes shape to accomplish accommodation for close focusing.

直径约9毫米，厚4毫米，晶状体提供了眼睛约20%的折射率。Hecht将其比作一个小小的透明洋葱，有约22000层细薄的层。其折射率从中心约1.406到外层约1.386，使其成为一种梯度折射率透镜。它具有可塑性，能够改变形状以实现近距离聚焦。

The term cataract is used to describe the condition of clouding or darkening of this lens.

‘白内障’一词用于描述这种透镜的混浊或变暗状况。
 Index

Vision concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 参考 Hecht，第二版 第5.7节
 
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Aqueous Humor

房水

The anterior chamber of the eye is filled with the watery "aqueous humor" which has an index of refraction of about 1.336. It is positioned immediately behind the cornea. The larger chamber of the eye is filled with the gelatinous "vitreous humor", which has an index of refraction of about 1.337 .

眼球的前房充满着一种透明的‘房水’，其折射率约为1.336。它位于角膜之后。眼球较大的腔体充满着凝胶状的‘玻璃体’，其折射率约为1.337。
 Index

Vision concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 参考 Hecht，第二版 第5.7节
 
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Vitreous Humor

玻璃体液

The large chamber of the eye is filled with the gelatinous "vitreous humor", which has an index of refraction of about 1.337 . The front chamber of the eye, immediately behind the cornea, is filled with the watery "aqueous humor" which has an index of refraction of about 1.336.

人眼的前部腔室充满着胶状的‘玻璃体’，其折射率约为1.337。紧接角膜之后的后部腔室充满着水样的‘房水’，其折射率约为1.336。

The index of refraction of both of the interior fluids of the eye are very close to that of water, n= 4/3 = 1.333 .

眼内流体的折射率非常接近水的折射率，n= 4/3 = 1.333。
 Index

Vision concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 参考 Hecht，第二版 第5.7节
 
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Cataracts

白内障

Cataract example courtesy of Dr. J. A. Ayres, M.D.

白内障示例由J. A. Ayres博士提供

When the inner lens of the eye becomes darkened or opaque, the condition is called a cataract. The lens may be surgically replaced with a plastic lens. This can have dramatic results in restoring vision to the eye. The implanted lens is of fixed focal length, so it is not capable of accommodation like the natural lens. This is usually not a major concern, because persons who develop cataracts after age 60 do not have much accommodation remaining anyway because the inner lens has become less pliable with age.

当眼睛的内透镜变暗或变得不透明时，这种情况称为白内障。透镜可以被手术替换为塑料透镜。这可以显著改善视力。植入的透镜具有固定的焦距，因此无法像自然透镜一样进行调节。这通常不是大问题，因为60岁以后患白内障的人，由于内透镜变得不够灵活，已经几乎没有调节能力了。
 Index

Vision concepts

Reference
Hecht, 2nd Ed.
Sec. 5.7
索引 视觉概念 参考 Hecht，第二版 第5.7节
 
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