Refraction The optical component is concerned with producing a reduced inverted image on the retina. The eye's optical system consists of not only two but four surfaces—two on the<unk> , two on the lens. Rays are refracted toward the midline. Distant rays, due to their parallel nature, converge to a point on the retina. The<unk>  admits light at the greatest angle. The aqueous and vitreous humors both have a refractive index of 1.336-1.339, whereas the<unk>  has a refractive index of 1.376. Because the change in refractive index between<unk>  and aqueous humor is relatively small compared to the change at the air–cornea interface, it has a negligible refractive effect, typically -6 dioptres. The<unk>  is considered to be a positive meniscus lens. In some animals, such as species of birds, chameleons and a species of fish, the<unk>  can also focus. Transparency The<unk>  becomes opaque after death(provenance: genus Bos) Upon death or removal of an eye the<unk>  absorbs the aqueous humor, thickens, and becomes hazy. Transparency can be restored by putting it in a warm, well-ventilated chamber at 31 °C (88 °F, the normal temperature), allowing the fluid to leave the<unk>  and become transparent. The<unk>  takes in fluid from the aqueous humor and the small blood vessels of the limbus, but a pump ejects the fluid immediately upon entry. When energy is deficient the pump may fail, or function too slowly to compensate, leading to swelling. This arises at death, but a dead eye can be placed in a warm chamber with a reservoir of sugar and glycogen that generally keeps the<unk>  transparent for at least 24 hours. The endothelium controls this pumping action, and as discussed above, damage thereof is more serious, and is a cause of opaqueness and swelling. When damage to the<unk>  occurs, such as in a viral infection, the collagen used to repair the process is not regularly arranged, leading to an opaque patch (leukoma).
Cornea
Apnea
Hyperpnea
Bronchospasm
Orthopnea
Tachypnea
Hypopnea
Cyclospasm