Eyes

"The eye is the organ of sight (vision) in humans and animals. The eye works by transforming light waves into visual images. Eighty percent of all information received by the human brain comes from the eyes. Eye color is created by the amount and type of pigment in the iris. Multiple genes inherited from each parent determine a person’s eye color. The eye is a slightly asymmetrical globe, about an inch in diameter. The front part of the eye (the part you see in the mirror) includes:
• The iris (the pigmented part)
• The cornea (a clear dome over the iris)
• The pupil (the black circular opening in the iris that lets light in)
• The sclera (the white part)
• The conjunctiva (an invisible, clear layer of tissue covering the front of the eye, except the cornea)"

Eye pressure

Elevated intraocular pressure is called ocular hypertension, meaning that the pressure inside the eye is higher than normal. Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Ocular hypertension is an eye pressure greater than 21 mm Hg. One of the most common threats to vision is glaucoma, damage to the nerve that takes visual signals from the eye to the brain, is often caused by elevated intraocular pressure.