What is refractive surgery?
Refractive surgery corrects your vision by changing the shape of the cornea, the transparent layer that covers the outer surface of the eye. Eye surgeons at UW Health Eye Clinics currently perform several types of refractive surgery:
- Photorefractive keratectomy (PRK) uses an excimer laser to remove a thin layer of the cornea to correct nearsightedness, farsightedness and astigmatism
- Laser In Situ Keratomileusis (LASIK) involves the use of a special instrument to raise a flap of corneal tissue, the excimer laser is then used to remove a thin layer of cornea underneath to treat nearsightedness, farsightedness and astigmatism
- IntraLASIK is the first blade-free laser technology using a laser to make a safer, more precise corneal flap during LASIK surgery
- Custom LASIK uses a wavefront analyzer to guide the treatment of additional imperfections in the optical system of the eye called higher order optical aberrations. This customized treatment can reduce the risk of glare, halos around lights or ghost images and deliver better results than current conventional treatment
To understand how refractive surgery corrects your vision, it helps to understand how the eye works.
How does the eye work?
The eye functions like a camera. Light comes in through the cornea, which focuses the light rays as they pass through the pupil and the lens. The iris, which surrounds the pupil, works like a camera shutter and controls the amount of light that enters the eye. In normal eyes, the cornea and lens bend light so that it focuses directly on the retina, the light sensitive tissue in the back of the eye. The retina changes light into electrical impulses that travel via the optic nerve to the brain.
Poor vision results when the cornea and the lens focus light too far in front of or behind the retina. Corrective lenses work by allowing the light to focus directly on the retina.
What is nearsightedness (myopia)?
When someone is nearsighted, light entering the eye is focused in front of the retina, instead of directly on it. People with myopia see near objects more clearly, while far objects appear blurry and out of focus.
Myopia is an inherited condition, which usually starts in childhood and stabilizes in the late teens or early twenties.
What is farsightedness (hyperopia)?
Farsightedness or hyperopia is a condition that occurs when light entering the eye is focused behind the retina. People with mild farsightedness have difficulty seeing objects up close but distant objects may be seen clearly. Higher amounts of hyperopia may result in the inability to see objects well at any distance.
What is astigmatism?
Astigmatism is the eye condition that occurs when the curvature of the cornea is not uniform, causing light to fall unevenly on the retina. This irregularity makes objects appear blurry or “ghosted.”
How does refractive surgery correct vision?
Laser vision correction uses an excimer laser to treat nearsightedness, farsightedness, and astigmatism. One laser pulse removes 1/4000 millimeter of tissue, an amount so small it would take 200 pulses of the laser to etch through a human hair. Controlled by a computer, the laser is an extremely accurate tool that your doctor can use to reshape your cornea. The results of your eye exam are entered into the computer, which calculates the precise depth and pattern of tissue to be removed. Because the laser does not generate heat, surrounding tissue is unharmed.