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Glossary of Terms

1. Astigmatism
   
2. Bowman's Layer
   
3. Cornea
   
4. Topographer
   
5. Diopters
   
6. Epithelium
   
7. Excimer Laser
   
8. Farsighted
   
9. Hyperopia
   
10. LASIK
    
11. Lens
    
12. Microkeratome
    
13. Monovision
    
14. Myopic
    
15. Nightsighted
    
16. Presbyopia
    
17. PRK
    
18. Radial Keratotomy
    
19. Refraction
    
20. Refractive Surgery
    
21. Retina
    
22. Stromal Tissue
    

Astigmatism

Astigmatism is caused by an uneven or asymmetrical curvature of the cornea, which prevents the eye from focusing clearly at any distance. Astigmatism causes certain amounts of distortion or pitched images because of the uneven bending of the light rays entering the eye.

Bowman's Layer

The Bowman's Layer is the next level of corneal tissue, immediately underneath the eye’s protective epithelium.

Cornea

The cornea is the eye's primary focusing element and when healthy, is composed of transparent, sturdy tissue that allows light to enter the eye without distortion.

Corneal Topographer

A corneal topographer is an instrument that maps the cornea to diagnose its elevation.

Diopters

Refractive errors are measured in "diopters". Nearsighted people have negative diopters and farsighted people have positive diopters.

Epithelium

The epithelium is a very fine protective outer layer of tissue on the front surface of the eye, covering the cornea. The epithelium regenerates itself every few days.

Excimer Laser

The excimer laser is the actual device that is used in many vision correction procedures. It is a cool laser that changes the shape of the cornea by eliminating tissue.

Farsighted

Farsightedness or hyperopia occurs when the cornea is too flat or the length of the eyeball is too short. As light enters the eye, the visual image focuses behind the retina, resulting in a blurred or distorted view.

Hyperopia

Hyperopia or farsightedness occurs when the cornea is too flat or the length of the eyeball is too short. As light enters the eye, the visual image focuses behind the retina, resulting in a blurred or distorted view.

LASIK

Laser Assisted in-situ Keratomileusis combines the advantages of a skilled surgeon and the excimer laser. In this procedure, a microkeratome first creates a thin flap of tissue on the cornea. The flap is folded back and the laser gently sculpts the cornea, altering the shape to correct the curvature. The flap is returned to its original position, adhering without stitches. LASIK is a proven procedure for treating higher degrees of nearsightedness and astigmatism.

Lens

The lens of the eye focuses the light entering through the pupil, directing it to the retina. The curvature of the lens adjusts to focus at different distances.

Microkeratome

A microkeratome is an automated surgical instrument which uses a blade to create a very thin flap of corneal tissue as the initial step in certain refractive surgery procedures.

Monovision

Monovision is an approach in some cases to solving the problem of presbyopia. It involves leaving one eye slightly nearsighted while correcting the other to see well at a distance.

Myopic

Myopia or nearsightedness occurs when the cornea is too steep relative to the length of the eyeball. As light enters the eye, this causes the visual image to focus in front of the retina, resulting in a blurred or distorted view.

Nearsighted

Nearsightedness or myopia occurs when the cornea is too steep relative to the length of the eyeball. As light enters the eye, this causes the visual image to focus in front of the retina, resulting in a blurred or distorted view.

Presbyopia

Presbyopia hits nearly everyone around middle age, when the lens loses some of its flexibility, making it harder to focus on objects that are held up close, such as a book. The "arm's length pose" while reading is a good indication presbyopia is setting in. Because it's unrelated to refractive error, there is a good chance that patients who have had refractive surgery will have to wear glasses for prespbyopia.

PRK

Since it was first developed in 1987, over 1,000,000 Photorefractive Keratectomy (PRK) procedures have been performed. PRK uses an excimer laser to gently reshape the surface of the cornea. Because the excimer laser is a cold laser, it does not burn the tissue. It produces a gentle beam of light which removes microscopic corneal layers, usually only 10-15% of the cornea's total thickness. This process, known as photoablation, changes the shape of the cornea, resulting in an image which is more finely focused on the retina, restoring clearer vision.

Radial Keratotomy

Radial Keratotomy or RK, is the earliest form of refractive surgery. In RK, the surgeon uses a knife with a diamond blade to cut radial like incisions on the peripheral area of the cornea. These incisions cause the cornea to weaken and flatten, thereby changing the shape of the eye and correcting myopia.

Refraction

When the cornea is misshaped and light doesn't focus properly on the retina, the eye has a refractive problem. The three most common refractive errors are: nearsightedness, when you can't see objects far away; farsightedness, when you can't see objects up close; and astigmatism, when you have trouble focusing on any object.

Refractive Surgery

Refractive surgery is the term which describes all of the methods used to surgically correct the curvature of the cornea to restore the focus point on the retina.

Retina

Located at the back of the eye, the retina's photosensitive cells convert light images into electrical impulses for the optic nerve. The optic nerve sends those impulses to the visual part of the brain, where they are interpreted into what we know as "sight".

Stromal Tissue

Stromal tissue refers to the central layers of the cornea. It comprises the majority of the corneal structure.