|
|
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.
There are 60,000 miles of blood vessels in every adult human.
Ether was used widely for surgeries but became less popular because of its flammability and its tendency to cause vomiting. In England, it was quickly replaced by chloroform, but this agent caused many deaths and lost popularity.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
![Glaucoma. (a) A buildup of pressure within the eye cavities, often caused by a blockage of vessels t](https://biology-forums.com/gallery/47/medium_14755_14_10_12_6_36_55_93952400.jpeg)
![Dopamine cannot cross the blood–brain barrier. Levodopa, its precursor, can. Once levodopa crosses ...](https://biology-forums.com/gallery/28/medium_482573_23_04_17_10_52_24_282931688.jpeg)