Eyes: The Path of Light

The eye is the ultimate light-gathering device. Although it seems automatic to us, the process of seeing involves many details.

When light enters the eye, it first encounter the tear film. This is a thin, three-layered coating of moisture. Normally the tear film is clear, but if it contains debris or matter, then light cannot pass through without distortion.

The next structure is the cornea, which is a seven-layered tissue. Its unique structure makes it clear, like a watch face. However, if there is clouding or scarring, the light will not be able to get through properly.

After passing through the watery aqueous fluid, light goes through the pupil and strikes the lens. The lens helps focus incoming light. If the lens becomes cloudy with a cataract, the light will be distorted.

Behind the lens is a chamber filled with a clear, jelly-like substance known as the vitreous. Like the other structures, the vitreous is normally clear. However, if there has been internal bleeding or infection, the vitreous may not be transparent. This can cause decreased vision.

Finally the light strikes the retina, the inner lining of the eye. The nine-layered retina contains light receptor cells called rods and cones. They gather the light and send it into the optic nerve. The optic nerve exits at the back of the eye and extends to the brain, where what we see is interpreted.

Each of these structures is related to the other, and each is important for good vision.