欲曉眼睛的光學原理，何不就沿著光徑

角膜→房水【前室】→虹膜【瞳孔】→晶狀體→玻璃體【後部】→視網膜

，從『角膜』之『屈光』能力開始。先讀維基百科詞條︰

角膜

角膜又稱黑睛，是眼睛最前面的透明部分，覆蓋虹膜、瞳孔及前房 ，並為眼睛提供大部分屈光力。加上晶狀體的屈光力，光線便可準確地聚焦在視網膜上構成影像。在人眼的折光系統中，角膜的折光能力是最強的，因為它直接和空氣接觸^[1]。

角膜有十分敏感的神經末梢，如有外物接觸角膜，眼瞼便會不由自主地合上以保護眼睛。為了保持透明，角膜並沒有血管，透過淚液及房水獲取養份及氧氣。

人類角膜直徑約11.5毫米，中心厚度約有0.5至0.6毫米，邊緣厚度則約0.6至0.8毫米。

角膜過凸是真性近視的一個重要特徵，因此也是角膜塑形鏡與雷射手術（LASIK等）防治真性[近視]方法作用的部位^[2]。

人工眼角膜

臺灣生技廠商在2005年開始投入上億經費研究，將臺灣鯛魚鱗片製成人工眼角膜，由於人和魚沒有共同疾病，不會有傳染病的疑慮，使用上安全性較高。

Cornea

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye’s total optical power.^[1][2] In humans, the refractive power of the cornea is approximately 43 dioptres.^[3] While the cornea contributes most of the eye’s focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to “tune” the focus depending upon the object’s distance. Medical terms related to the cornea often start with the prefix “kerat-” from the Greek word κέρας, horn.

Structure

The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid. Because transparency is of prime importance the cornea does not have blood vessels; it receives nutrients via diffusion from the tear fluid through the outside surface and the aqueous humour through the inside surface, and also from neurotrophins supplied by nerve fibres that innervate it. In humans, the cornea has a diameter of about 11.5 mm and a thickness of 0.5–0.6 mm in the center and 0.6–0.8 mm at the periphery. Transparency, avascularity, the presence of immature resident immune cells, and immunologic privilege makes the cornea a very special tissue. The cornea has no blood supply; it gets oxygen directly through the air. Oxygen first dissolves in the tears and then diffuses throughout the cornea to keep it healthy.^[4]

It borders with the sclera by the corneal limbus.

The most abundant soluble protein in mammalian cornea is albumin.^[5]

In lampreys, the cornea is solely an extension of the sclera, and is separate from the skin above it, but in more advanced vertebrates it is always fused with the skin to form a single structure, albeit one composed of multiple layers. In fish, and aquatic vertebrates in general, the cornea plays no role in focusing light, since it has virtually the same refractive index as water.^[6]

 

再回顧球面折射『成像條件』︰

。

【SymPy 參考】

pi@raspberrypi:~  ipython3
Python 3.4.2 (default, Oct 19 2014, 13:31:11) 
Type "copyright", "credits" or "license" for more information.

IPython 2.3.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: from sympy import *

In [2]: from sympy.physics.optics import FreeSpace, FlatRefraction, ThinLens, GeometricRay, CurvedRefraction, RayTransferMatrix

In [3]: init_printing()

In [4]: 空氣折射率 = 1.0003

In [5]: 角膜折射率 = 1.376

In [6]: 角膜前緣半徑 = 7.8

In [7]: 角膜後緣半徑 = 6.4

In [8]: 角膜厚度 = 0.6

In [9]: 房水折射率 = 1.336

In [10]: 角膜前部 = CurvedRefraction(角膜前緣半徑, 空氣折射率, 角膜折射率)

In [11]: 角膜前部
Out[11]: 
⎡         1                   0        ⎤
⎢                                      ⎥
⎣-0.0350048449612403  0.726962209302326⎦

In [12]: 角膜中段 = FreeSpace(角膜厚度)

In [13]: 角膜中段
Out[13]: 
⎡1  0.6⎤
⎢      ⎥
⎣0   1 ⎦

In [14]: 角膜後部 = CurvedRefraction(角膜後緣半徑, 角膜折射率, 房水折射率)

In [15]: 角膜後部
Out[15]: 
⎡         1                  0        ⎤
⎢                                     ⎥
⎣0.00467814371257483  1.02994011976048⎦

In [16]: 角膜 = 角膜後部 * 角膜中段 * 角膜前部

In [17]: 角膜
Out[17]: 
⎡ 0.978997093023256   0.436177325581395⎤
⎢                                      ⎥
⎣-0.0314730051162211  0.750768045123416⎦

In [18]: 角膜後部 * 角膜前部
Out[18]: 
⎡        1                  0        ⎤
⎢                                    ⎥
⎣-0.031374750499002  0.74872754491018⎦

 

怎麼看都只有 點幾 ？為什麼不是 耶？？因為各家的數據來源不同，若用維基百科詞條數據做計算︰

In [19]: 維基角膜 = CurvedRefraction(11.5/2, 角膜折射率, 房水折射率) * FreeSpace(角膜厚度) * CurvedRefraction(11.5/2, 空氣折射率, 角膜折射率)

In [20]: 維基角膜
Out[20]: 
⎡ 0.971509100101112   0.436177325581395⎤
⎢                                      ⎥
⎣-0.0438479088773699  0.750998710364912⎦

In [21]: 

 

果然有 的乎！！所以一般引用『統計平均』數據時，務須謹慎也☆☆