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How and Why LASIK Surgery Works to Correct Vision

What is LASIK?
LASIK (Laser Assisted in Situ Keratomileusis) is a surgical procedure for correcting refractive errors of the eye, such as myopia (nearsightedness), hyperopia (farsightedness) and astigmatism. Because the procedure is relatively painless and vision improvement is achieved by the next day, LASIK has become the procedure of choice for people looking to improve their vision. In fact, according to the American Academy of Ophthalmology, LASIK’s 95% patient satisfaction level is the highest rating for any surgical procedure.

How Clear and Focused Vision Works
Think of the eye as a small screening room. The cornea, which is the lens on the front surface of the eye, and the internal crystalline lens form the eye’s focusing mechanism. The retina, found on the back wall of the eye, is the screen. For those with 20/20 vision, light rays (and the images they carry) pass through the cornea, are redirected to the crystalline lens and are then brought to a clear point focus directly on the retina.

Why Vision Becomes Unclear and Unfocused
Approximately 60 percent of us have some imperfection in the shape of the various components of the eye, causing a poorly focused image on the retina. The most common of these refractive errors are: Myopia, or nearsightedness, where light rays reach a point focus before they reach the retina; hyperopia, or farsightedness, where light rays have not yet reached a focus when they hit the retina; and astigmatism, where due to irregular corneal curvature, light rays do not come to a single point focus.

Correcting Vision Problems with LASIK
Similar to traditional eyeglass lenses, LASIK surgery corrects these conditions by redirecting the rays of light so that they focus precisely on the retina. The difference is eyeglasses redirect light before it reaches the cornea, LASIK changes the cornea itself. By use of computer-controlled lasers, the cornea is precisely sculpted into a new shape. Myopes’ corneas are flattened to elongate their focus, hyperopes’ corneas are made steeper to shorten their focus and astigmats’ corneas are smoothed to create a single focus.

What Happens Before LASIK Surgery
Typically, an instrument called a pachymeter is used to gauge the exact thickness of the cornea and a corneal topographer is used to photograph and create a detailed map of the lens surface. Some surgeons do a wavefront analysis of the eye. This procedure sends light waves into the cornea creating an even more precise map. Data from these tests go into the computer which assists the surgeon in controlling where and how much the cornea needs to be shaped in order to get the required light refraction.

What Happens During LASIK Surgery
There are 3 basic steps to the actual LASIK procedure. First, using either a microkeratome (a bladed device) or a laser keratome, the surgeon cuts a thin circular flap on the surface of the cornea which is then pushed back, exposing the inner (stroma) layer of the lens. Then, with the patient fully awake and focusing on a target light, the surgeon uses pulses from the excimer laser to vaporize stroma cells until the desired change in shape is achieved. Finally, the flap is carefully flipped back in place where it will act as a natural bandage while the wound heals.

Why LASIK is Different from Other Vision Correction Procedures
The advantage that LASIK offers over previous refractive correction procedures is the flap. Because the corneal reshaping is done down in the stroma layer, LASIK delivers quicker visual recovery and less pain. It should be noted, however, that not all LASIK patients can be brought to 20/20 vision. According to the Eyecare Education Council, approximately 90 percent of LASIK patients reach 20/40 acuity or better, which is the acuity required by most states to drive a car without corrective lenses.

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