Learn The Eye And How It Uses Light To Help You See!

by admin on 24/05/2009


Diagram of the human eye

Not at all a simple organ, the eye is one of those organs that tends to keep all its complexities to itself.  Many people don’t even know the multiple actions that go on inside of the eye that allow them to actually see objects in front or to the side of them.  Just in short are some of the parts of the eye mostly discussed below and their functions.

Let’s begin with the cornea.  This is the part of the eye that is generally overlooked due to its lack of color.  It is totally transparent, and it is the part of the eye to which a contact lens adheres.   The cornea has a very important function.  In fact, it is so important that any abnormality on it can cause vision loss or distortion.  The main thing that the cornea does is focus rays of light.  As a matter of fact, most of the rays that are reflected onto the eye are focused by the cornea.  This is reason that injury, abnormal shaping, corneal ulcers, dry eyes etc are detrimental to vision and need to be treated immediately as it may cause the transparency and lubrication of the cornea to diminish making it impossible to focus light rays.

One of the next important parts of the eye responsible for focusing light is the lens, the crystalline lens.  In a sense, it works together with the cornea as the two are the only parts of the eye that are responsible for the same thing – reflecting light rays.  The lens reflects less light rays than the cornea, however, it has one thing up on the cornea and that is it can change shape in order to change focusing power!  The cornea cannot do this.  Basically, the crystalline lens is able to accommodate (change shape, thus, changing power) depending on what that individual is doing whether it be reading a book or looking at a distance.  A steeper curve for things close up and a flatter curve for things far away.

As for the retina, this is where all the images that come from the two reflectors above are sent.  The retina is responsible for everything that one sees basically as there is a central portion called the macula that consists of two types of cells called rods and cones.  The rods are the cells that handle things like night vision or situations where there is little to no light along with peripheral vision.  The cones, however, handle all of what a person sees in color while giving a person great central vision.

Finally, the optic nerve head also known as the optic disc.  This is the part of the eye where there is absolutely no vision at all.  Yes, everyone has a blind spot, but not everyone is legally blind.  The reason there is no vision at the optic disc is because the cells responsible for vision, rods and cones, are not present there!  So what is the optic nerve purpose if it has no rods or cones?  Simple.  It is responsible for taking the messages received by the retina from the “reflectors” and transporting them to the brain from the eye.  This is a very simple explanation, but the whole process is far more complex.  Problems with the optic nerve can eventually result in blindness if not treated promptly i.e. glaucoma.

A quick overview:

Light comes toward an eye.  It hits the cornea and is refracted to the lens which then focuses it through vitreous to the retina. From there the optic nerve transports the image to the brain creating the image.

Again, this is simplified.  The iris, pupil, axons, cilliary muscles etc play huge roles in how light is transmitted as well, but for the most part, as long as the pathway is clear back to a healthy retina and the image is able to be transmitted to the brain via a healthy optic nerve(ON), then a person will be able to see providing normal circumstances.

{ 1 comment… read it below or add one }

tara December 25, 2009 at 19:42

I find every topic very useful especially now that i am preparing for my ABO exam May of next year.

Please continue to educate us with regards to eye optics.

Sincerely,

Tara

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