隨著晶珠模型探討，終於到了眼睛成像光徑之最後一站
角膜→房水【前室】→虹膜【瞳孔】→晶狀體→玻璃體【後部】→視網膜
玻璃體
玻璃體又稱玻璃狀液、神膏（英文 Vitreous humor），是眼球內無色透明的膠狀物質，表面覆蓋著玻璃體膜。玻璃體填充於晶狀體與視網膜之間，約占眼球內腔的4/5。
玻璃體對視網膜起支撐作用，使視網膜與色素上皮緊貼。支撐作用減弱時，容易導致視網膜脫落；若玻璃體混濁，會影響視力。
Vitreous body
The vitreous body is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous humour or simply “the vitreous”.
Structure
The vitreous humour is a transparent, colorless, gelatinous mass that fills the space in the eye between the lens and the retina. It is present at birth and remains unchanged throughout one’s life.[1] Produced by cells in the non-pigmented portion of the ciliary body, the vitreous humor is derived from embryonic mesenchyme cells, which degenerate after birth.
The vitreous humour is in contact with the retina and helps to keep it in place by pressing it against the choroid. It does not adhere to the retina, except at the optic nerve disc. It is also connected to the ora serrata (where the retina ends anteriorly), at the Wieger-band, the dorsal side of the lens. It is however, not connected at the macula, the tiny spot in the retina which gives us our “detail” and central vision.
Composition
Its composition is similar to that of the cornea, but the vitreous contains very few cells. It is composed mostly of phagocytes, which remove unwanted cellular debris in the visual field, and hyalocytes, which turn over the hyaluronan.
The vitreous humor contains no blood vessels, and 98-99% of its volume is water (as opposed to only 75% in the cornea). In addition to water, the vitreous consists of salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibrils with glycosaminoglycan, hyaluronan, opticin, and a wide array of proteins. Despite having little solid matter, the fluid is substantial enough to fill the eye and give it its spherical shape. The lens, on the other hand, is tightly packed with cells.[2] The vitreous humour has a viscosity two to four times that of water, giving it a gelatinous consistency. It has a refractive index of 1.336.[3]
| Solute | Mean concentration | Units | Reference |
|---|---|---|---|
| Sodium | 146.7 | mmol/L | [4] |
| Potassium | 5.73 | mmol/L | [4] |
| Chloride | 121.6 | mmol/L | [4] |
| Calcium | 1.13 | mmol/L | [4] |
| Magnesium | 0.9 | mmol/L | [4] |
| Glucose | 2.97 | mmol/L | [4] |
| Lactate | 3.97 | mmol/L | [4] |
| Osmolality | 289.5 | mOsm/kg | [4] |
| Beta-hydroxybutyrate | 0.094 | mmol/L | [4] |
| Copper | 0.52 | µmol/L | [4] |
| Selenium | 0.104 | µmol/L | [4] |
| Iron | 3.11 | µmol/L | [4] |
| Ferritin | 19.52 | µg/L | [4] |
| Transferrin | 0.088 | g/L | [4] |
| Manganese | 110.7 | nmol/L | [5] |
抵達視覺神經網絡之界面
視網膜
視網膜又稱視衣，是脊椎動物和一些頭足綱動物眼球後部的一層非常薄的細胞層。它是眼睛裏面將光轉化為神經信號的部分。
視網膜含有可以感受光的視杆細胞和視錐細胞。這些細胞將它們感受到的光轉化為神經信號。這些信號被視網膜上的其它神經細胞處理後演化為視網膜神經節細胞的動作電位。視網膜神經節細胞的軸突組成視神經。視網膜不但有感光的作用，它在視覺中也有重要作用。在形態形成的過程中，視網膜和視神經是從腦中延伸出來的。
視網膜上的血管的結構每個人都不一樣，因此可以用來做生物特徵識別。
視網膜
解剖學
人的視網膜分10個層（由最外到最內)：
- 視網膜色素上皮
- 感光層——包括視桿細胞及視錐細胞
- 外界膜——這個層隔開感光細胞的內部與其細胞核
- 外核層——又稱外顆粒層，由光感受器細胞核組成
- 外叢狀層——由光感受器細胞的軸突及雙極細胞(en:Bipolar neuron)樹突水平細胞突起組成，它們之間的接觸稱為突觸
- 內核層——又稱內顆粒層，由雙極細胞、水平細胞、無長突細胞、Muller細胞的胞核組成
- 內叢狀層——主要由雙極細胞的軸突及神經節細胞的樹突組成，並以突觸形式相接觸
- 神經節細胞層——這個層含有神經節細胞的細胞核，視神經從這裡開始
- 神經纖維層——主要為神經節細胞的軸突
- 內界膜
視網膜的不同層級
Retina
The retina (UK /ˈrɛtɪnə/ RET-i-nə, US /ˈrɛtᵊnə/ RET-(ə-)nə, pl. retinae, /ˈrɛtiniː/; from Latin rēte, meaning “net”) is the third and inner coat of the eye which is a light-sensitive layer of tissue. The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon; thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue.[1][2] It is the only part of the CNS that can be visualized non-invasively.
The retina is a layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. For vision, these are of two types: the rods and cones. Rods function mainly in dim light and provide black-and-white vision while cones support the perception of colour. A third type of photoreceptor, the photosensitive ganglion cells, is important for entrainment and reflexive responses to the brightness of light.
Neural signals from the rods and cones undergo processing by other neurons of the retina. The output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. Several important features of visual perception can be traced to the retinal encoding and processing of light.
希望讀者已經學會了解讀各種光學設備的方法！！？？