• Lasik, refractive errors types, different procedures besides Lasik
• Nos’ of LASIK
• Risk factor assessment before Lasik
• Risks in LASIK
• Complications of LASIK
• What to expect before, during, after LASIK
• Wavefront LASIK
• Monovision treatment for presbyopes above 40 years age

LASIK is a surgical procedure intended to reduce a person's dependency on glasses or contact lenses. The goal of this literature is to provide objective information to the public about LASIK surgery.

LASIK stands for Laser-Assisted In Situ Keratomileusis, and is a procedure that permanently changes the shape of the cornea, the clear covering of the front of the eye, using an excimer laser. An instrument called a microkeratome, is used to cut a flap in the cornea. A hinge is left at one end of this flap. The flap is folded back revealing the stroma, the middle section of the cornea. 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.

What is LASIK?
The cornea is a part of the eye that helps focus light to create image on the retina. It works in much the same way that the lens of a camera focuses light to create an image on film. The bending and focusing of light is also known as refraction. Usually the shape of the cornea and the eye are not perfect and the image on the retina is out-of-focus (blurred) or distorted. 
These imperfections in the focusing power of the eye are called refractive errors. There are three primary types of refractive errors: myopia, hyperopia and astigmatism. Persons with myopia, or nearsightedness, have more difficulty seeing distant objects as clearly as near objects. Persons with hyperopia, or farsightedness, have more difficulty seeing near objects as clearly as distant objects. Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are common. Glasses or contact lenses are designed to compensate for the eye's imperfections. 
Surgical procedures aimed at improving the focusing power of the eye are called refractive surgery. In LASIK surgery, precise and controlled removal of corneal tissue by a special laser reshapes the cornea changing its focusing power. Other types of refractive surgery Radial Keratotomy or RK and Photorefractive Keratectomy or PRK are other refractive surgeries used to reshape the cornea. In RK, a very sharp knife is used to cut slits in the cornea changing its shape. PRK was the first surgical procedure developed to reshape the cornea, by sculpting, using a laser. Later, LASIK was developed. The same type of laser is used for LASIK and PRK. Often the exact same laser is used for the two types of surgery. The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser. In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath. In LASIK, a flap is cut in the stromal layer and the flap is folded back. Another type of refractive surgery is thermokeratoplasty in which heat is used to reshape the cornea. The source of the heat can be a laser, but it is a different kind of laser than is used for LASIK and PRK. Other refractive devices include corneal ring segments that are inserted into the stroma and special contact lenses that temporarily reshape the cornea (orthokeratology).Neurovision treatment is another type of FDA approved eye treatment available for low grades of refractive errors and does not involve any surgery or medications.

What is FDA approval? 
What the FDA regulates In the United States, the Food and Drug Administration (FDA) regulates the sale of medical devices such as the lasers used for LASIK. Before a medical device can be legally sold in the U.S., the person or company that wants to sell the device must seek approval from the FDA. To gain approval, they must present evidence that the device is reasonably safe and effective for a particular use, the "indication." Once the FDA has approved a medical device, a doctor may decide to use that device for other indications if the doctor feels it is in the best interest of a patient. The use of an approved device for other than its FDA-approved indication is called "off-label use." The FDA does not regulate off-label use or the practice of medicine. The first refractive laser systems approved by FDA were excimer lasers for use in PRK to treat myopia and later to treat astigmatism. However, doctors began using these lasers for LASIK (not just PRK), and to treat other refractive errors (not just myopia). Over the last several years, LASIK has become the main surgery doctors use to treat myopia. More recently, some laser manufacturers have gained FDA approval for laser systems for LASIK to treat myopia, hyperopia and astigmatism and for PRK to treat hyperopia and astigmatism. 

When is LASIK not for me? 
You are probably NOT a good candidate for refractive surgery if:

• You are not a risk taker. Certain complications are unavoidable in a percentage of patients, and there are no long-term data available for current procedures.
• You required a change in your contact lens or glasses prescription in the past year. This is called refractive instability. Patients who are: 
• In their early 20s or younger, 
• Whose hormones are fluctuating due to disease such as diabetes, 
• Who are pregnant or breastfeeding, or 
• Who are taking medications that may cause fluctuations in vision, 
  are more likely to have refractive instability and should discuss the possible additional risks with their doctor. 
• You have a disease or are on medications that may affect wound healing. Certain conditions, such as autoimmune diseases (e.g., lupus, rheumatoid arthritis), immunodeficiency states (e.g., HIV) and diabetes, and some medications (e.g., retinoic acid and steroids) may prevent proper healing after a refractive procedure. 
• You actively participate in contact sports. You participate in boxing, wrestling, martial arts or other activities in which blows to the face and eyes are a normal occurrence. 
• You are not an adult. Currently, no lasers are approved for LASIK on persons under the age of 18. 

Risk Factor assessment before LASIK:
You should be screened for the following conditions or indicators of risk:

• Blepharitis. Inflammation of the eyelids with crusting of the eyelashes,that may increase the risk of infection or inflammation of the cornea after LASIK. 
• Large pupils. Younger patients and patients on certain medications may be prone to having large pupils under dim lighting conditions. This can cause symptoms such as glare, halos, starbursts, and ghost images (double vision) after surgery. In some patients these symptoms may be debilitating. 
• Thin Corneas. The cornea is the thin clear covering of the eye that is over the iris, the colored part of the eye. Most refractive procedures change the eye’s focusing power by reshaping the cornea (for example, by removing tissue). Performing a refractive procedure on a cornea that is too thin may result in complications. 
• Previous refractive surgery (e.g., RK, PRK, LASIK). Additional refractive surgery may not be recommended. The decision to have additional refractive surgery must be made in consultation with your doctor after careful consideration of your unique situation. 
• Dry Eyes. LASIK surgery tends to aggravate this condition. 

What are the risks?
Most patients are very pleased with the results of their refractive surgery. 
However, like any other medical procedure, there are risks involved. That's why it is important for you to understand the limitations and possible complications of refractive surgery.Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system.

• Some patients loose vision. Some patients may loose some lines of vision on the vision chart that cannot be corrected with glasses, contact lenses, or surgery as a result of treatment. 
• Some patients develop debilitating visual symptoms. Some patients develop glare, halos, and/or double vision that can affect nighttime vision. Even with good vision on the vision chart, some patients do not see as well in situations of low contrast, such as at night or in fog, after treatment as compared to before treatment. 
• You may be under treated or over treated. Only a certain percent of patients achieve 20/20 vision without glasses or contacts. You may require additional treatment, but additional treatment may not be possible. You may still need glasses or contact lenses after surgery. This may be true even if you only required a very weak prescription before surgery. If you used reading glasses before surgery, you may still need reading glasses after surgery. 
• Some patients may develop dry eye syndrome. As a result of surgery, your eye may not be able to produce enough tears to keep the eye moist and comfortable. Dry eye not only causes discomfort, but can reduce visual quality due to intermittent blurring and other visual symptoms. Though dry eye most of the time resolves by itself over 4 to 6 months,Intensive drop therapy and use of plugs or other procedures may be required.
• Results are generally not as good in patients with very large refractive errors. You should discuss your expectations with your doctor and realize that you may still require glasses or contacts after the surgery.

Complications of LASIK:
Even the best screened patients under the care of most skilled surgeons can experience serious complications.

• During surgery. Malfunction of a device or other error, such as cutting a flap of cornea through and through instead of making a hinge during LASIK surgery, may lead to discontinuation of the procedure or irreversible damage to the eye. 
• After surgery. Some complications, such as migration of the flap, inflammation or infection, may require another procedure and/or intensive treatment with drops.

Under the care of an experienced doctor, carefully screened candidates with reasonable expectations and a clear understanding of the risks and alternatives are likely to be happy with the results of their refractive procedure. 

What should I expect before, during, and after surgery?

What to expect before, during, and after surgery will vary from doctor to doctor and patient to patient. 

Before Surgery

If you decide to go ahead with LASIK surgery, you will need an initial or baseline evaluation by your eye doctor to determine if you are a good candidate. This is what you need to know to prepare for the exam and what you should expect:
If you wear contact lenses, it is a good idea to stop wearing them before your baseline evaluation and switch to wearing your glasses full-time. Contact lenses change the shape of your cornea for up to several weeks after you have stopped using them depending on the type of contact lenses you wear. Not leaving your contact lenses out long enough for your cornea to assume its natural shape before surgery can have negative consequences. These consequences include inaccurate measurements and a poor surgical plan, resulting in poor vision after surgery. These measurements, which determine how much corneal tissue to remove, may need to be repeated at least a week after your initial evaluation and before surgery to make sure they have not changed, especially if you wear semi soft or hard lenses. If you wear:

• soft contact lenses, you should stop wearing them for 2 weeks before your initial evaluation. 
• toric soft lenses or rigid gas permeable (RGP) lenses, you should stop wearing them for at least 3 weeks before your initial evaluation. 
• hard lenses, you should stop wearing them for at least 4 weeks before your initial evaluation. 
  You should tell your doctor:
• about your past and present medical and eye conditions 
• about all the medications you are taking, including over-the-counter medications and any medications you may be allergic to 
  The day before surgery, you should stop using:
• creams, lotions, makeup, perfumes

These products as well as debris along the eyelashes may increase the risk of infection during and after surgery. Make sure someone accompanies you during after Lasik to bring you home after surgery.

During Surgery
The surgery should take less than 30 minutes. You will lie on your back.The laser system includes a large machine with a microscope attached to it and a computer screen.

A numbing drop will be placed in your eye, the area around your eye will be cleaned, and an instrument called a lid speculum will be used to hold your eyelids open. A ring will be placed on your eye and very high pressures will be applied to create suction to the cornea. Your vision will dim while the suction ring is on and you may feel the pressure and experience some discomfort during this part of the procedure. The microkeratome, an instrument, is attached to the suction ring. The microkeratome is to make a flap in your cornea. 

The microkeratome and the suction ring are then removed. You will be able to see, but you will experience fluctuating degrees of blurred vision during the rest of the procedure. The doctor will then lift the flap and fold it back on its hinge, and dry the exposed tissue.
The laser will be positioned over your eye and you will be asked to stare at a light. This is not the laser used to remove tissue from the cornea. This light is to help you keep your eye fixed on one spot once the laser comes on. NOTE: If you cannot stare at a fixed object for at least 60 seconds, you may not be a good candidate for this surgery.
When your eye is in the correct position, your doctor will start the laser. At this point in the surgery, you may become aware of new sounds and smells. The pulse of the laser makes a ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair. A computer controls the amount of laser energy delivered to your eye. Before the start of surgery, your doctor will have programmed the computer to vaporize a particular amount of tissue based on the measurements taken at your initial evaluation. After the pulses of laser energy vaporize the corneal tissue, the flap is put back into position. 
A shield or glasses would be placed over your eye at the end of the procedure as protection, since no stitches are used to hold the flap in place. It is important for you to wear this shield to prevent you from rubbing your eye and putting pressure on your eye while you sleep, and to protect your eye from accidentally being hit or poked until the flap has healed.

After Surgery:
Immediately after the procedure, your eye may burn, itch, or feel like there is something in it. You may experience some discomfort, or in some cases, mild pain and you may be suggested to take a mild pain reliever. Both your eyes may tear or water. Your vision will probably be hazy or blurry. You will instinctively want to rub your eye, but don't! Rubbing your eye could dislodge the flap, requiring further treatment. In addition, you may experience sensitivity to light, glare, starbursts or haloes around lights, or the whites of your eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery. You should plan on taking a few days off from work until these symptoms subside. 
You should see your doctor within the first 24 to 48 hours after surgery and at regular intervals thereafter as instructed. You may also be advised to use artificial tears to help lubricate the eye. 

You should wait one to three days following surgery before beginning any non-contact sports, depending on the amount of activity required, how you feel, and your doctor's instructions.
To help prevent infection, you may need to wait for up to two weeks after surgery or until you are advised otherwise before using lotions, creams, or make-up around the eye. You should also avoid swimming and using hot tubs or whirlpools for 1-2 months. 
Strenuous contact sports such as boxing, football, karate, etc. should not be attempted for at least four weeks after surgery. It is important to protect your eyes from anything that might get in them and from being hit or bumped.
During the first few months after surgery, your vision may fluctuate.
· It may take up to three to six months for your vision to stabilize after surgery. 
· Glare, haloes, difficulty driving at night, and other visual symptoms may also persist during this stabilization period. If further correction or enhancement is necessary, you should wait until your eye measurements are consistent for two consecutive visits at least 3 months apart before re-operation.

Wavefront LASIK:
The term ' wavefront' is the way the natural light pathway goes in the eye through the entire optics. This is supposed to be a smooth path in an ideal eye. As the light travels through the other optical system inside the eye, like the lens, vitreous jelly etc. it undergoes further degradation. This is acceptable to a certain extent and that is why the eye surgeons have reached a 6/6 or 20/20 criteria as normal sight. However, when these errors or 'higher order aberrations' as they are known, exist to an extent in which they need to be treated then wavefront treatments [Custom LASIK] are a must for such patients.

Monovision for presbyopia above 40 years age

Monovision is one clinical technique used to deal with the correction of presbyopia, the gradual loss of the ability of the eye to change focus for close-up tasks that progresses with age. The intent of monovision is for the presbyopic patient to use one eye for distance viewing and one eye for near viewing. This practice was first applied to fit contact lens wearers and more recently to LASIK and other refractive surgeries. With contact lenses, a presbyopic patient has one eye fit with a contact lens to correct distance vision, and the other eye fit with a contact lens to correct near vision. In the same way, with LASIK, a presbyopic patient has one eye operated on to correct the distance vision, and the other operated on to correct the near vision. In other words, the goal of the surgery is for one eye to have vision worse than 20/20, the commonly referred to goal for LASIK surgical correction of distance vision. Since one eye is corrected for distance viewing and the other eye is corrected for near viewing, the two eyes no longer work together. Though most patients tolerate this well but it may result in poorer quality vision and a decrease in depth perception. These effects of monovision are most noticeable in low lighting conditions and when performing tasks requiring very sharp vision. Therefore, you may need to wear glasses or contact lenses to fully correct both eyes for distance or near when performing visually demanding tasks, such as driving at night, operating dangerous equipment, or performing occupational tasks requiring very sharp close vision (e.g., reading small print for long periods of time). 
Many patients cannot get used to having one eye blurred at all times. Therefore, if you are considering monovision with LASIK, make sure you go through a trial period with contact lenses to see if you can tolerate monovision, before having the surgery performed on your eyes.