EYE.

The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help to provide a three dimensional, moving image, normally coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors and is possibly capable of detecting a single photon.

 The eye is made up of three coats, or layers, enclosing various anatomical structures. The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera. The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris. The innermost is the retina, which gets its oxygenation from the blood vessels of the choroid (posteriorly) as well as the retinal vessels (anteriorly).

Your eye is a slightly asymmetrical globe, about an inch in diameter. The front part (what you see in the mirror) includes:

• Iris: the colored part
• Cornea: a clear dome over the iris
• Pupil: the black circular opening in the iris that lets light in
• Sclera: the white of your eye
• Conjunctiva: a thin layer of tissue that covers the entire front of your eye, except for the cornea

·         Eye Conditions

Age-related macular degeneration: Causes loss of central vision as you get older.

Cataract: A clouding of your eye’s internal lens. It can cause blurred vision.

 Conjunctivitis: Also known as pinkeye, it’s an infection or inflammationof the conjunctiva, the clear layer that covers the front of your eye. Allergies, viruses, or a bacterial infection can all cause it.

Diabetic retinopathy: High blood sugardamages blood vessels in the eye. Eventually, they start to leak or overgrow in your retina, threatening your vision.

·         Dry eye: Either your eyes don’t produce enough tears, or the tears are of poor quality. Medical problems like lupus, scleroderma, and Sjogren's syndromeare often to blame.

·         Glaucoma: This progressive loss of vision comes from increased pressure inside the eye. Your peripheral vision(side vision) will go first, then your central vision will follow. It can go undetected for years.