The structure of the eye is composed of a single, outwardly curved (convex) clear lens, the cornea, at the front and a lengthy 'fiber optic' cable, the optic nerve, extending from the back.

It is essentially an empty structure, except for the colored iris, a circular band of muscles that controls the size of the pupil, which allows variable amounts of light to pass to the back inside the surface of the eye. The amount of pigmentation of the iris determines its color. Blue eyes, for example, have very little amount of pigment, and black eyes have the most.

The pupil is the central transparent area, that is controlled by the ciliary muscles in the iris, that make the pupil smaller when the amount of light is excessive, and vice versa.

Light rays pass through the clear cornea, which due to its curved surface, is able to bend (refract) the light rays. These light rays are concentrated together and pass through the pupil. Then, they go through the normally clear lens which has two curved surfaces, the front and the back. Therefore, these light rays are bent (refracted) two more times on their trip to the back of the eye.

The light rays travel to the back surface of the eye through the vitreous, a clear jelly which fills the space between the back of the lens and the retina, the inside lining of the back surface of the eye which contains specialized cells which convert light energy into electrical impulses.

These cells are either called rods, specialized for black and white images, or cones, that mainly process color images. In dim light, we use our rods, which cannot work in bright light. To deal with bright or moderate light, we use our cones, that beside providing color vision, they also process some aspects of black and white vision and the ability to discern fine detail.

What is truly amazing about the eye is how part of these cells in the retina (photosensitive cells) actually are a six inch appendage of the cell, the axon, which joins with other axons to compose the optic nerve which travels to the brain stem, the very top of the spinal cord, located at the very center of the brain. There, each axon connects (synapses) with a cell or cells, and the axon of the receiving cell(s) travels another six inches to the back of the brain, the occipital lobe, where it synapses with a brain cell(s) to produce what we call vision.

Therefore, the major functions of these parts of the visual system are composed by:

Cornea: Refracts light rays

Pupil: Controls the amount of light entering the eye

Lens: Refracts light rays

Vitreous: Light traverses this space

Retina: Converts light energy to electrical energy

Optic Nerve: Transmits electrical energy from the retina to the brain stem

Brain Stem: Intermediate 'relay station' for visual fibers

Occipital Cortex: Final destination. Converts electrical energy to visual images

A "Perfect Eye" would therefore have:

a clear and unobstructed path from the front of the eye to the back of the eye.

the proper balance between the length of the eye and the curvatures of the three refracting surfaces.

properly functioning cells in the retina and brain which allow the conversion of light energy to electrical energy, the transmission of this energy, and the interpretation of the energy into what we call vision.

Unfortunately, most people do not have "perfect eyes".

Eyes that are too long or have too much refracting power (from the cornea and the lens) are nearsighted eyes, as images are focused in front of the retina. The image received by the retina is not a 'dot for dot' representation of what the image viewed by the eye. Instead, each of these 'dots' of light becomes enlarged to form a 'disc' of light with a consequent spread of the dot image to adjacent parts of the retina. This is what causes blurring of vision.

The opposite results when eyes or too short or have too little refracting poser. These eyes are farsighted, as images are focused (or would be) behind the retina. The same type of dot to disc representation occurs.

When light rays that are vertically oriented are not refracted the same amount as the light rays that are horizontally oriented, this condition is called astigmatism. An example would be when that eye looks at a building that is built as a square, it would appear as a rectangle with different vertical and horizontal dimensions being visualized. This example refers to strictly vertical (90 degrees) and strictly horizontal (0 degrees); astigmatism can occur at any angle between 0-180 degrees.

On a more dynamic level, the eye can possess no refractive error whatsoever but is unable to adjust to near images by increasing its refractive powers. This condition is termed presbyopia and normally affects persons in their 40s and early 50s. The mechanisms within the eye that can increase the curvature of the lens (accommodation) become less efficient and external plus lenses are necessary to bring the near images into focus.

The eye is truly like a camera because it not only requires proper focusing (refraction) but it requires a clear media through which light rays must pass. Any loss of clarity of the structures through which these light rays must pass will interfere with their successful interpretation within the visual cortex of the brain. Examples of disorders which might cause this scattering or absorption of light rays are opacities or swelling of the cornea (scars, edema, abrasions, etc.), opacification of the lens (cataract), and cloudiness of the vitreous (hemorrhage or inflammation.)

Also, the receiving tissue, the retina must be functioning properly, as opposed to aged related macular degeneration, in which there is deterioration of the most important part of the retina, the macula, which is responsible for our finest and our reading vision.

The range of patologies which can be treated with Laser Eye Surgery are:

Myopia (nearsightedness): -0.75 diopters to -10.0 diopters

Hyperopia (farsightedness): +0.75 diopters to +5.0 diopters

Astigmatism (associated with myopia): 0 to 4.0 diopters

Presbyopia (the eye's diminished ability to focus that occurs with aging).

Traditionally, many of these conditions were often treated with prescription glasses or contact lenses. Today, a number of innovative Laser Eye Surgery procedures are widely available.

LASIK is a surgical procedure intended to reduce a person's dependency on glasses or contact lenses. The goal of this Web site is to provide objective information to the public about LASIK surgery. See other sections of this site to learn about what you should know before surgery, what will happen during the surgery, and what you should expect after surgery. There is a glossary of terms and a checklist of issues for you to consider, practices to follow, and questions to ask your doctor before undergoing LASIK surgery.

Lasik and Rk Eye Surgery Information and Resources

Learning about LASIK and Radial Keratotomy (RK)

The “LASIK” in Lasik eye surgery stands for Laser-Assisted In Situ Keratomileusis. It is a procedure that permanently changes the shape of the cornea, the clear covering of the front of the eye, using an solid state excimer laser. A mechanical microkeratome (blade device) or a laser keratome (a laser device) is used to make an incesion in a flap in the cornea. A hinge is left at one end of this flap. The flap is folded back revealing the stroma of the eye, the middle section of the cornea. Light pulses from a computer-controlled laser vaporize a portion of the stroma and the flap is replaced. There are other techniques and many new terms related to LASIK that you may hear about.