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AMARIS Custom LASIK

In trying to understand the LASIK procedure we must first learn about how the eye works. Here are a few basic concepts:

The eye functions like a camera: There are focusing elements at the front of the eye and film that records the image at the back of the eye. In the eye, there are two focusing elements, the cornea, which is the clear dome that covers the coloured part of the eye, and the crystalline lens that gives us the ability to see close and far and fine tunes the image. Most of the focusing power, roughly two-thirds lies in the cornea. The coloured part of the eye known as the iris, encircles the pupil, which is the central black portion and controls the entry of light into the eye. Continuing with the camera analogy, the film or retina at the back of the eye images what we see, sending it along the optic nerve to our brain.

Why do some people need a prescription? In people that require prescription eyeglasses or contact lenses, the cornea and lens do not focus light correctly at the back of the eye. Glasses or contact lenses are required to re-focus the image sharply. In nearsightedness or myopia, only near objects are clear. Nearsighted eyes tend to be longer and the cornea more pointy causing distant images to be focused in front of the retina producing a blurred image on the retina. In farsightedness or hyperopia, the eye is shorter and the cornea tends to be flatter having less corneal power, therefore not allowing the image to focus before it reaches the retina. If the patient is young or has strong focusing muscles they can bring the image into focus on the retina. In astigmatism, the cornea is shaped like a football and there are two points of focus created, blurring images at all distances.

The simplest way to understand LASIK: First, it is important to appreciate that LASIK is a two-step procedure. The first step is the creation of the corneal flap, and the second step is the treatment of the inner cornea with the patient’s prescription. When the corneal flap is opened, the surgeon places a new curve onto the inner corneal surface, changing the shape of the cornea to focus light more precisely on the retina, taking the place of their glasses and contacts. Read more... Imagine the cornea like a book, composed of roughly 540 pages, with each page representing one micron. In LASIK, the book is opened to approximately page 100, then pages are removed by an excimer laser. The cornea is reshaped to correctly focus the light on the retina based on the prescription. The book is then closed at the end of the procedure and appears unchanged.

The corneal flap can be created with two techniques: Either a mechanical microkeratome, a very refined ophthalmic instrument, much like a carpenters plane or a Femtosecond laser. Dr. Machat has performed over twenty thousand microkeratome corneal flaps, however in 2003 when the femtosecond laser was introduced to Canada, he was the first surgeon to adopt the more advanced technique.

The prescription can also be treated in one of two ways: Either with a standard laser pattern, which utilizes a single central prescription reading and a standardized pattern of laser pulses or with a Customized laser pattern based on hundreds of prescription measurements across the entire pupil area. Dr. Machat in 2000, was the first surgeon in Canada to perform a Custom LASIK procedure and helped pioneer the technology lecturing and training surgeons worldwide.

In Custom All Laser LASIK, the corneal flap is created with a Femtosecond laser rather than with a mechanical microkeratome as in the standard LASIK procedure. The laser-created protective flap is then lifted and the prescription correction is then applied with an Excimer laser. In this All Laser LASIK procedure, the safety profile is improved dramatically and most of the corneal flap complications eliminated. In a Customized procedure, the prescription correction is based on a wavefront analysis which measures prescription 25 times more precisely than a standard prescription, to the closest 1/100 of a diopter rather than the closest ¼ of a diopter. As well, the custom procedure targets the correction of visual irregularities and optimizes the final shape of the eye to reduce night vision difficulties. In 2003, Dr. Machat was the first surgeon in Canada to perform Custom All Laser LASIK, combining the two advancements, sometimes also referred to as Custom Bladeless LASIK since no mechanical microkeratome is utilized.

The visual irregularities are not ones that glasses are able to correct, so there is a potential of achieving a better quality of vision. It is important to recognize, that although the wavefront based treatment profile corrects for visual irregularities, patients healing responses can vary. Therefore the final results cannot be guaranteed. More importantly, what a wavefront based treatment plan does is create the optimum corneal shape which helps reduce spherical aberration, the irregularity most responsible for inducing night glare. In simpler terms, it is like a tailor made suit rather than one off the rack.

As discussed above, and like glasses, a Standard laser procedure uses a single point to measure your prescription, whereas the Custom procedure applies a grid pattern to the eye over the pupil, and measures the amount of correction required within each and every square. The light rays are focused not just for the center of the pupil but into the mid-periphery, so that when the pupil expands in low light conditions or in patients with larger pupils, these light rays are well focused. Custom or Wavefront generated patterns do not produce the severe starbursting or halos that was commonly experienced with earlier Standard lasers.

The Schwind AMARIS 750S at Crystal Clear Vision has over 1000 points of measurement over the pupil area, four times as many as the previous system Dr. Machat previously used and that is used by other clinics in Toronto and across North America. The AMARIS 750S system is also capable of treating both total or simply corneal aberrations, which is critical in patients over 50 who have crystalline lens changes as well. The corneal wavefront program is equally important in patients who have had previous laser eye or refractive surgery and require further treatment.