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Updated: May 9, 2025
The action of the lens is aided by several refractive media in the eye. These media are the cornea, the aqueous humor, and the vitreous humor. By reason of their shape and density these media refract the rays of light, and bring them to a focus upon the retina, thus aiding in producing a sharp and distinct image of the object.
His eyelids quiver, the black veins in his throat knot up, he gasps. I bend lower: 'his breath comes hurriedly: his eyes open and fix upon me: they are red, vitreous but conscious: then I know he will speak, he is going to the next moment his half-strangled voice reaches my ear. He is speaking, and that which I hear him say, I write: no more, no less, no different.
One pattern is purely geometrical; another has birds, dogs, hares, baskets of flowers, and floral scrolls in octagons and squares set diagonally between them; both marble and vitreous pastes are used, as well as gold tesseræ. Inscriptions were also found in letters of the third or beginning of the fourth century: " *ore Felix hic crevisti hic Felix" and "Cyriacus vivas."
Now, he has before learned that without this lens an eye would by the aqueous and Vitreous humors alone form an image upon the retina, but this image would be indistinct from the light not being sufficiently refracted, and likewise from having a colored fringe round its edges.
Also, heavy drops of rain still bespattered our heads and shoulders, and at every peal of thunder the tree quivered and creaked until the strident din around us gave one the illusion of being afloat in a narrow caique. Meanwhile at every flash of the lightning's glare, we could see slanting ribands of rain cutting the air with a network of blue, glistening, vitreous lines.
We have to take into account the large scleral wound made, and the fact that this lies close to the ciliary body. The sudden release of all tension and the simultaneous weakening of the supports of the lens and vitreous body create very unfavorable conditions under which to make the crucial step of the operation.
Lucretius attributes to accident the discovery of the fusion of the metals; a person in touching a shell-fish observes that it emits a purple liquid as a dye, hence the Tyrian purple; clay is observed to harden in the fire, and hence the invention of bricks, which could hardly fail ultimately to lead to the discovery of porcelain; oven glass, the most perfect and beautiful of those manufactures you call chemical, is said to have been discovered by accident; Theophrastus states that some merchants who were cooking on lumps of soda or natron, near the mouth of the river Belus, observed that a hard and vitreous substance was formed where the fused natron ran into the sand.
In this state the animals can see, but dimly and imperfectly, as a man sees after having been couched. Some of the offspring of these animals have, by natural variation, merely a portion of the membrane which separates the aqueous from the vitreous humor a little thickened in its middle part, a little swelled out.
Any process that increases the volume of the contents of the vitreous chamber, as hemorrhage, neoplasm, profuse serous or plastic exudation, may by pushing iris and lens forward produce an attack of acute glaucoma. Buphthalmos. Ophth. In all of the cases in which the eye has been examined microscopically obliteration of Schlemm's canal has been reported.
It is a significant fact that even in man, according to the high authority of Virchow, the beautiful crystalline lens is formed in the embryo by an accumulation of epidermic cells, lying in a sack-like fold of the skin; and the vitreous body is formed from embryonic subcutaneous tissue.
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