LASIK reshapes the cornea, the front-most, transparent part of the eye, to achieve spectacle freedom for people with near-sightedness, far-sightedness, or astigmatism. A C-shaped flap is made on the superficial cornea, the flap is then lifted and folded over its "hinge" to expose the corneal "bed," laser energy is applied on the corneal "bed" to reshape it, then the flap is put back in place to facilitate healing and to maximize comfort after the procedure. Below is a detailed description of the steps in LASIK.
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What Does LASIK Treat?
Myopia, or near-sightedness, is when a person can see well up close without glasses, but cannot see far without glasses. Depending on the severity of myopia, one may need to bring objects extremely close to her face to see them. Myopia is the most common indication for LASIK vision correction surgery.
Hyperopia, or far-sightedness, is somewhat of a misnomer. Hyperopic persons actually have a hard time seeing near and far without glasses. Even if hyperopia is mild, uncorrected distance vision is fair, but near vision without glasses becomes very difficult. For many hyperopes, LASIK vision correction can help them regain their vision without the hindrance of glasses.
Astigmatism is not a disease, but rather an altered shape of the cornea, the crystal clear and front-most part of the human eye. According to the American Academy of Ophthalmology, approximately one-third of all people have astigmatism. Like a basketball, a cornea without astigmatism is a perfect circle, and its curvature is exactly the same everywhere on the cornea, 360 degrees all-around. An astigmatic cornea is like an American football, where it is steeper in its short axis and less steep in its long axis. Even in a perfectly healthy eye, astigmatism blurs one's vision at all distances, and prescription glasses are required for good vision.
Around age 40-45, most people start losing the ability to focus on near objects. This affects reading, computer work, and hobbies like sewing or solving puzzles. This is called presbyopia. The most common treatment for presbyopia is reading or prescription glasses, but if you are a good candidate, LASIK could help you regain your reading vision. Just ask your physician during your LASIK evaluation.
What is Monovision?
This is a great option for presbyopic patients over the age of 40 who wish to achieve spectacle independence. Monovision is when one eye sees better at distance, and the other eye sees better at near. Just as a person usually has a dominant hand (right vs. left handedness), a person usually has a dominant eye and a non-dominant eye. Typically, the dominant eye sees at distance, and the non-dominant eye sees at near, but this is not a hard and fast rule. A minority of people actually see at distance with their non-dominant eye and at near with their dominant eye. Just like monovision contact lenses, monovision LASIK can help people with presbyopia achieve spectacle independence.
Photorefractive keratectomy, or PRK, does not require a corneal flap. Instead, the superficial layer of the cornea is removed with a brush or a fine blade, exposing the "bed" of the middle corneal layer. The excimer laser is then used to reshape the cornea to correct myopia, hyperopia, and/or astigmatism. The remaining superficial corneal defect is left open, and a bandage contact lens is placed on the eye for comfort. After a few days, the cornea will regenerate itself and heal over the superficial defect, after which the bandage contact lens can be removed. In general, healing after PRK takes slightly longer, and patients may be more uncomfortable after surgery. However, PRK is the preferred vision correction procedure for persons with previous corneal transplants, Map-Dot-Fingerprint corneal dystrophy, very thin corneas, or corneas with previous radial keratotomy (RK) incisions.
Contraindications to LASIK/PRK:
Some corneas have an abnormal shape or unique properties that preclude them from undergoing laser vision correction surgery, such as:
- Pellucid Marginal Degeneration
- Severe dry eye / keratoconjunctivitis sicca (KCS)
- Very thin corneas
- Hereditary corneal dystrophies
At your LASIK or PRK evaluation, your eyes will undergo rigorous testing to exclude these corneal diseases or abnormalities to ensure that laser vision correction is safe and effective for your eyes.
Contact Lens Users
Measurements of one's natural corneal shape is critical in the pre-operative calculations used to perform LASIK or PRK surgery. Since contact lenses rest directly on the cornea, the cornea's natural shape will, over time, conform to the shape of the contact lens itself. Therefore, when pre-operative measurements for LASIK or PRK are performed immediately after a contact lens is removed from one's eye, such measurements will not be accurate because the natural corneal shape has been altered by the contact lens. As a general rule, before your LASIK or PRK screening visit, you should:
- Discontinue soft contact lens use 1-2 weeks prior to your visit.
- Discontinue hard contact lens use 3-4 weeks prior to your visit.