LASIK

Laser In-Situ Keratomileusis, or LASIK, the most commonly performed type of laser surgery, is generally a safe and effective treatment for a wide range of common vision problems. Specifically, LASIK involves the use of a laser to permanently change the shape of the cornea, the clear covering of the front of the eye. LASIK is a quick and often painless procedure, and for the majority of patients, the surgery improves vision and reduces the need for corrective eyewear. However, as LASIK is a surgical procedure conducted on a delicate part of the eye, it is crucial that potential candidates are well educated on the benefits and risks of the procedure, understand the importance of a thorough screening by their physician, and maintain realistic expectations about the procedure’s outcome.

Who is Right for Laser Eye Surgery?

While many individuals are considered good candidates for LASIK, there are some who do not meet the generally accepted medical criteria to ensure a successful laser vision procedure. Individuals that are not deemed good candidates given today’s technology may be able to have the surgery in the future, as technology advances and new techniques are refined. Anyone considering laser eye surgery must have a thorough examination by an ophthalmologist that will help determine, in consultation with the patient, whether or not the LASIK procedure is right for them. Based on various conditions and circumstances, all LASIK candidates will fall into one of the following three broad categories.

The Ideal LASIK Candidate

The ideal candidate includes those who:

Are over 18 years of age and have had a stable glasses or contact lens prescription for at least two years. Have sufficient corneal thickness (the cornea is the trans-parent front part of the eye). A LASIK patient should have a cornea that is thick enough to allow the surgeon to safely create a clean corneal flap of appropriate depth. Are affected by one of the common types of vision problems or refractive error – myopia (nearsightedness), astigmatism (blurred vision caused by an irregular shaped cornea), hyperopia (farsightedness), or a combination thereof (e.g., myopia with astigmatism). Several lasers are now approved by the U.S. Food and Drug Administration (FDA) as safe and effective for use in LASIK, but the scope of each laser’s approved indication and treatment range is limited to specified degrees of refractive error. Do not suffer from any disease, vision-related or otherwise, that may reduce the effectiveness of the surgery or the patient’s ability to heal properly and quickly. Are adequately informed about the benefits and risks of the procedure. Candidates should thoroughly discuss the procedure with their physicians and understand that for most people, the goal of refractive surgery should be the reduction of dependency on glasses and contact lenses, not their complete elimination.

The ‘Less Than Ideal’

In some cases, a surgeon may still be able to perform the procedure safely, given that the candidate and physician have adequately discussed the benefits and risks, and set realistic expectations for the results. Candidates in this category include those who:

Have a history of dry eyes, as they may find that the condition worsens following surgery. Are being treated with medications such as steroids or immunosuppressants, which can prevent healing, or are suffering from diseases that slow healing, such as autoimmune disorders. Have scarring of the cornea.

More often, factors exist that may keep an individual from being a candidate immediately, but do not preclude the individual from being a candidate entirely. Candidates in this category include those who:

Are under age 18. Have unstable vision, which usually occurs in young people. Doctors recommend that, prior to undergoing LASIK, candidates’ vision has stabilized with a consistent glasses or contact lens prescription for at least two years. Are pregnant or nursing. Have a history of ocular herpes within one year prior to having the surgery. Once a year has passed from initial diagnosis of the disease, surgery can be considered. Have refractive errors too severe for treatment with current technology. Although FDA-approved lasers are available to treat each of the three major types of refractive error – myopia, hyperopia and astigmatism – current FDA-approved indications define appropriate candidates as those with myopia up to -12 D, astigmatism up to 6 D and hyperopia up to +6D.

The Non-LASIK Candidate

Certain conditions and circumstances completely preclude individuals from being candidates for LASIK surgery. Non-candidates include individuals who:

Have diseases such as cataracts, advanced glaucoma, corneal diseases, corneal thinning disorders (keratoconus or pellucid marginal degeneration), or certain other pre-existing eye diseases that affect or threaten vision. Do not give informed consent. It is absolutely necessary that candidates adequately discuss the procedure and its benefits and risks with their surgeon, and provide the appropriate consent prior to undergoing the surgery. Have unrealistic expectations. It is critical for candidates to understand that laser eye surgery, as all surgical procedures, involves some risk. In addition, both the final outcome of surgery and the rate of recovery vary from person to person and even from eye to eye in each individual.

Excimer Lasers

The excimer laser has brought more accuracy to corneal surgery and vision correction than ever before. One pulse of the excimer laser removes 0.25 microns of tissue. To put this into perspective, a typical human hair is 70 microns in thickness. Surgeons have never had a device as accurate as the excimer laser in eye surgery.

Electron Micrograph of a Human Hair Ablated by the Excimer Laser

Why is Technology so Important for Laser Vision Correction

The Excimer Laser is one of the greatest inventions in ophthalmology. The Excimer Laser is the device that physically corrects your prescription during surgery. Because laser vision correction is based on the microscopic removal of corneal tissue at the molecular level it is impossible to achieve this type of accuracy manually. No other device has provided patients the opportunity to reduce or eliminate their dependency on glasses and contacts. Although many people perceive laser technology to be the same, there are vast differences between one laser versus another. One question that should be raised prior to your surgery is whether the laser being used is the newest in laser vision correction technology. By having your eyes treated with the newest in laser vision technology it increases your chances for a successful outcome.

Eyetracker

Not all eyetrackers are created equally. Ensure that the eyetracker has a sampling rate faster than 200 Hertz. The reason why this is so important is because your eye can twitch at a rate of 60 Hz. If your eye twitches faster or at the same speed as the eyetracker then the eyetracker may not be able to get the appropriate readings of the movement of the eye. In turn, the laser may not be able to place the right pulse of the laser in the appropriate section of the cornea because of the lack of information. What is also extremely important is the ability of the laser to react to the information being sent to it from the eyetracker. The response time of the laser must be very fast to ensure that each laser pulse is placed exactly on the appropriate part of the cornea. Even if the laser can sample the movement of the eye 1000 times but the laser reacts slowly to this information, the result is that the laser may be placing pulses on areas of the cornea based on old information. The best example of the relationship between the eyetracker and the laser is to try and imagine throwing a ball at a moving object that is going 200 miles an hour. Although you can see the moving object, your reflexes are too slow to adjust to the constant changes of the moving object. As a result, every time you throw the ball you are missing the moving object. Slow or older lasers work on the same principle. Although the eyetracker can see the eye moving, it is too slow to react and may miss the targeted area of the cornea. The ALLEGRETTO WAVE Excimer Laser encompasses both a 250 Hz eyetracker with the ability to react between 4 to 8 ms. This optimizes the ability of each pulse being placed on the appropriate spot on the cornea reducing erroneous misplaced pulses of the laser more common on older laser technology.

Beam Size and Profile

A small diameter laser beam or also known as spot size is very important for both accuracy and smoothness. An ideal beam size is approximately 1mm or less. If the size of the laser beam is larger the result is that the beam is too large to make fine adjustments throughout the cornea. Imagine filling a fishbowl with marbles compared to filling is with sand. The marbles allow gaps while the sand contours and fills the fishbowl exactly. While beam size is critical so is the type of laser beam that is being used. A gaussian beam allows for the smoothest corneal surface as compared to non-gaussian beams. The result is that with a small beam less than 1 mm with a gaussian profile allows for the proper and accurate treatment of the smallest curvatures of the cornea and also allowing for a smooth corneal surface.

Speed

When having your eyes treated, the speed of each laser pulse that is applied to the cornea is very important. If the laser is too slow and you have a high prescription, the exposed flap may shrink because of the time it takes to correct your vision. Ensure that the laser is fast preferably 200 Hertz and that it has a high-energy profile. This will only improve your chances for a successful procedure. Older lasers only apply 10 to 60 pulses of the laser per second. The ALLEGRETTO WAVE Excimer Laser applies 200 individual laser pulses per second ensuring the fastest treatment for optimal results. An example of this would be a car that only goes 10 km/h. If you were trying to go 20 kilometers it would take you 2 hours to get there but if you were driving 200 km/h it would only take you 6 minutes. In this case, the longer it takes you to have your eye treated, the higher the risk of an adverse result. Only the ALLEGRETTO WAVE Excimer Laser has the ability to provide fast and precise treatments increasing your likelihood for a successful procedure and decreasing your chances for complications due to dehydration of the flap and corneal surface.

Optical Zones

Optical Zone is the term used to describe the size of the treated area of the laser that will be applied to the surface of the cornea. Older generation lasers typically can only treat pupils no larger than 6.5mm since the largest optical zone they can use is 6.5 mm. If your pupils are larger than 6.5 mm then your chances for night vision problems increase significantly if your eyes are not treated with a laser that can provided larger optical zone ranges. Only the ALLEGRETTO WAVE Excimer Laser combines optical zones from 5.5mm to 8mm. This allows the physician to customize your treatment to maximize your desired outcome and reduce or eliminate night vision problems. Only the ALLEGRETTO WAVE Excimer Laser allows each patient to receive a truly customized treatment for pupil sizes up to 8mm. This not only increases your quality of vision during the day but also reduces or eliminates night vision.

Wavefront Adjusted Nomograms

The ALLEGRETTO WAVE Excimer Laser was designed from the ground up for wavefront treatments. Even during classic or standard treatments, the ALLEGRETTO WAVE Excimer Laser has incorporated wavefront data to its mathematical algorithms also know as Wavefront Adjusted Nomograms to calculate a truly maximized treatment for each patient. Unlike other lasers that were not designed for wavefront, the ALLEGRETTO WAVE Excimer Laser combines wavefront to every facet or its laser. The Wavefront adjusted derived nomogram provides patients the opportunity to enhanced outcomes and quality of vision.

PRK Surgery

What is PRK?

The PRK laser is computer-controlled and programmed by the surgeon to specifically address a patient's own unique corneal shape and refractive error. The laser produces a highly concentrated beam of light which flattens the front surface of the cornea by removing micro-thin layers of tissue. Photorefractive Keratectomy, or PRK, is an outpatient corneal surgery that can reduce or correct mild to moderate myopia. This is done by use of a laser that precisely reshapes the cornea. The goal of PRK is to reduce or eliminate dependency on glasses or contact lenses. Most of the people who have had PRK report they no longer need to wear glasses or contacts. In a large clinical trial, two-thirds of the patients who had PRK can see 20/20 or better without corrective lenses. 95% can see at least 20/40, well enough to pass a driver's test.