The eye is the most delicate and complex organ. It not only enables us to see the wondrous beauty around us but also adds great beauty to our face.
Your eyes are at work from the moment you wake up to the moment you close them to go to sleep. They take in tons of information about the world around you – shapes, colors, movements, and more.
Then they send the information to your brain for processing. This way the brain knows what’s going on outside of your body.
The eye structure comprises of various parts
The tough, outermost layer i.e. the white part of the eye is called the sclera. It maintains the shape of the eye. It is made of a tough material and has the important job of covering most of the eyeball. Attached to the sclera are the muscles that move the eye, called the extraocular muscles.
The cornea, a transparent dome, sits in front of the colored part of the eye. All light must first pass through the cornea when it enters the eye.
The choroid (or uveal tract) is the second layer of the eye. It contains the blood vessels that supply blood to structures of the eye. The front part of the choroid contains two structures.
The ciliary body – The ciliary body is a muscular area that is attached to the lens. It contracts and relaxes to control the size of the lens for focusing. That’s right – the lens actually changes shape right inside your eye! Try looking away from your computer and focusing on something way across the room. Even though you didn’t feel a thing, the shape of your lenses changed.
The iris – The iris is the colored part of the eye. The color of the iris is determined by the color of the connective tissue and pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is an adjustable diaphragm around an opening called the pupil.
The iris has two muscles:
The dilator muscle makes the iris smaller and the pupil larger, allowing more light into the eye.
The sphincter muscle makes the iris larger and the pupil smaller, allowing less light into the eye.
Pupil size can change from 2 millimeters to 8 millimeters. This means that by changing the size of the pupil, the eye can change the amount of light that enters it by 30 times.
The innermost layer is the retina — the light-sensing portion of the eye.
It contains rod cells, which are responsible for vision in low light, and cone cells, which are responsible for color vision and detail.
In the back of the eye, at the center of the retina, is the macula. In the center of the macula is an area called the fovea centralis. This area contains only cones and is responsible for seeing fine detail clearly.
The retina contains a chemical called rhodopsin, or “visual purple.” This chemical converts light into electrical impulses that the brain interprets as vision. The retinal nerve fibers collect at the back of the eye and form the optic nerve, which conduct the electrical impulses to the brain.
The spot where the optic nerve and blood vessels exit the retina is called the optic disk. This area is a blind spot on the retina because there are no rods or cones at that location. However, you are not aware of this blind spot because each eye covers for the blind spot of the other eye.
When a doctor looks at the back of your eye through an ophthalmoscope, here’s the view:
Inside the eyeball there are two fluid-filled sections separated by the lens. The larger, back section contains a clear, gel-like material called vitreous humor. The smaller, front section contains a clear, watery material called aqueous humor. The aqueous humor is divided into two sections called the anterior chamber (in front of the iris) and the posterior chamber (behind the iris). The aqueous humor is produced in the ciliary body and is drained through the canal of Schlemm. When this drainage is blocked, a disease called glaucoma can result.
The lens is a clear, bi-convex structure about 10 mm (0.4 inches) in diameter. The lens changes shape because it is attached to muscles in the ciliary body. The lens is used to fine-tune vision.
Covering the inside surface of the eyelids and sclera is a mucous membrane called the conjunctiva, which helps to keep the eye moist. An infection of this area is called conjunctivitis (also called pink eye).
The eye is unique in that it is able to move in many directions to maximize the field of vision, yet is protected from injury by a bony cavity called the orbital cavity.
The eye is embedded in fat, which provides some cushioning. The eyelids protect the eye by blinking. This also keeps the surface of the eye moist by spreading tears over the eyes. Eyelashes and eyebrows protect the eye from particles that may injure it.
Tears are produced in the lacrimal glands, which are located above the outer segment of each eye. The tears eventually drain into the inner corner of the eye, into the lacrimal sac, then through the nasal duct and into the nose.
That is why your nose runs when you cry.Your eyes sometimes make more tear fluid than normal to protect themselves. This may have happened to you if you’ve been poked in the eye, if you’ve been in a dusty or smoking area, or if you’ve been near someone who’s cutting onions.
And how about the last time you felt sad, scared, or upset? Your eyes got a message from your brain to make you cry, and the lacrimal glands made many, many tears.
From the above mentioned function of each part of the eyes we see that they do some great things for us, so it is very important that we take the necessary steps to protect them.
