The eye, though small (approximately 2.54cm tall, 2.54cm deep and 2.3 cm wide), is a very complex organ that allows us to see our family members, oncoming traffic, and even scenery. Blindness is when your eye does not function properly. To explain this in full, I will first examine to normal workings of an eye.

There are sixteen parts of the eye. They are:
1.Slcera-keeps the eye in the correct shape.
2.Cornea- The cornea is the front part of the sclera. Light must pass through the cornea before it goes into the eye.
3.Extraocular muscles- Extraocular muscles are attached to the sclera and are the muscles that move the eye.
4.Choroid- The choroid is the second layer of the eye. It holds blood vessels that supply the eye with blood. There are two structures in the front part of the choroid.
5. The ciliary body- the ciliary body is a muscle that is attached to the lens. It grows or shrinks depending on how far away the object you are looking at is.
6.The iris- the iris is the colored part of the eye. The color of the iris is determined by the connective tissue and the pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is a circle around an opening called the pupil.
7.The Dilator- The dilator is a muscle in the iris that makes the iris smaller so it can allow more light into the pupil.
8.The Sphincter- The sphincter is the second muscle in the iris that makes the iris larger so the pupil is smaller and less light can get into the eye. The pupil size can change from 2mm to 8mm. that means from the pupil size, the eye can change the amount of light allowed into the eye by thirty times. 9.The Retina- The retina is the light-sensing part the eye. It has rod cells, which are for vision in low light, and cone cells, which are for color and detail. In the back of the eye is the macula. In the center of the macula is an area called the fovea centralis.

Thi Sclera- The sclera is the toughest part of the eye. It is also on the outermost part of the eye so it only contains cones and is for seeing fine detail. The retina contains a chemical called rhodopsin. This is the chemical that makes light into electrical impulses that the brain makes into vision.

10.Optic nerve- The optic nerve is formed from retinal nerve fibers collecting at the back of the eye. The optic nerve sends the electrical impulses to the brain.
11.Optic disk- The optic disk is the spot where the optic nerve and the blood vessels exit the retina. This area is a blind spot on the retina because there are no rods or cones there. Luckily, you’re not aware of this blind spot because each eye covers for the blind spot of the other eye.
12.Vitreous Humor- The vitreous humor is a clear, gel-like liquid in the large, back section of the eye.
13.Aqueous humor- The aqueous humor is in the small, front part of the eye. The lens divides the aqueous humor from the vitreous humor. The aqeous humor is divided into two parts. One is called the anterior chamber and it is located in front of the iris. The second part is called the posterior chamber and it is behind the iris.
14.Canal of Schlemm- After the aqueous humor is produced in the ciliary body it is drained through the canal of schlemm. Glaucoma is a disease caused when this drainage gets blocked.
15.The lens: The lens is clear and has about a 10mm diameter. The lens changes shape because it is attached to muscles in the ciliary body. The lens fine-tunes vision.
16.Conjunctiva- The conjunctiva is a mucous membrane that helps keep the eye moist. An infection in this area is called conjunctivitis or pink eye.

Now that you fully understand the basic workings of the eye, I will tech you about blindness. blindness is usually defined when your visual sight is less than 20/200 with corrective lenses. Now that you have learned some anatomy of the eye and how it functions, it becomes easier to understand how the following conditions can lead to blindness: 1. Cataracts - This is a cloud in the lens that blocks light from getting to the retina. It is more common as you age, but you can be born with a cataract. As it gets worse, it can need surgery to remove the lens and place an intraocular lens.

1. Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds in the eye. This makes the cells and nerve fibers in the back of the eye die. It can be treated with medications and surgery.

2. Diabetic retinopathy - People with diabetes can get blockage of blood vessels, leakage of blood vessels and scarring that can lead to blindness. You can treat this with laser surgery.

3. Macular degeneration - In some people, the macula (which is responsible for fine detail in the center of vision) can deteriorate with age for unknown reasons. This causes loss of central vision. This can sometimes be helped with laser surgery.

4. Trauma - Trauma or chemical injuries can cause enough damage to the eyes to prevent adequate vision.

5. Retinitis pigmentosa - This is an inherited disease that causes a degeneration of the retina and pigment. It first causes night blindness and then tunnel vision, which often gradually progresses to total blindness. There is no known treatment.

6. Trachoma - This is an infection caused by an organism called Chlamydia trachomatis. It is a common cause of blindness worldwide but is rare in the United States. It can be treated with antibiotics.

Color blindness is also a type of blindness. Color blindness is the inability to tell between different colors. The most common type is red-green color blindness. This is in 8 percent of males and 0.4 percent of females. It happens when the red or green cones are not present or not functioning properly. People with this problem are not completely unable to see red or green, but often confuse the two colors. This is an inherited disease and affects men more often since the color vision is located on the X chromosome. (Women have two X chromosomes, so the probability of inheriting at least one X with normal color vision is high; men have only one X chromosome to work with.). The inability to see any color, or seeing only in different shades of gray, is very rare.