Intralase SBK (Sub-Bowman’s Keratomileusis) is the name of a refractive surgery procedure deriving its name from the Intralase Corporation which is owned by Advanced Medical Optics (1), a division of Abbott Laboratories (2).
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Intralase SBK (sometimes referred to as “SBK”) is a method of Laser Vision Correction that employs a process called photodisruption to create a thinner flap than that usually created by a microkeratome. The procedure is essentially the same as Bladeless LASIK but with a different brand name. The process uses highly focused, femtosecond-duration laser pulses to divide material at the molecular level without impacting the surrounding tissue. Microscopic bubbles of carbon dioxide and water vapor are created at the points where the laser is focused. Thousands of these bubbles are precisely positioned to define the flap’s dimensions, as well as the location of the hinge. The surgeon can then lift the flap and perform corneal ablation using an excimer laser, which corrects refractive error in the eye. When the treatment is complete, the flap can be accurately repositioned due to its beveled edge.
Flap Thickness
Like Bladeless LASIK, Intralase SBK uses a computerized process to create a flap that is thinner and more precise than one made by traditional microkeratomy, which means the laser correction takes place much closer to the surface, similar to what occurs during a standard Photorefractive keratectomy (PRK) procedure. With a thinner flap – approximately 95 µm, versus 150 µm for traditional microkeratomy – the eye maintains its structural rigidity. Advocates of SBK explain that a thin flap combines the advantages of Blade LASIK and PRK without the disadvantages. Preserving the flap results in faster visual recovery, less discomfort, reduced risk of haze, and the thinness of the flap preserves the biomechanical properties of the cornea, which are weakened with traditional microkeratomy flaps. Recent studies have also shown that corneal sensitivity after SBK is similar to that after PRK. (3).
Blade versus Laser
Intralase SBK and Blade LASIK differ by more than just the thickness of the flap. A blade and a laser are different in that a blade cuts, whereas a laser sculpts. The laser can cut vertically as well as horizontally; it can engrave patterns in the side walls to enhance stability. This is particularly useful for corneal transplants, but the same versatility is also used in refractive surgery. A blade can only cut tangentially across the corneal surface, which means that the flap tends to be thinner in the centre, with more possibility of “buttonholing”, where the flap breaks through in the middle. By contrast, the laser can sculpt a curved flap, following the contours of the eye.
A well-publicized Intralase SBK study was conducted by Drs. Slade and Durrie in the United States (4), and tested 50 patients. One eye of each patient underwent Intralase SBK using the femtosecond laser to create a 100-µm flap, while the other eye underwent PRK. In the first three days, the Intralase SBK eyes had better uncorrected vision and much less discomfort, but after the first week, visual acuity in the two sets of eyes began to converge. After six months, the results for the groups were nearly identical. Dr. Stephen Slade reported that 100% of eyes that underwent Intralase SBK had 20/40 or better vision on day one and that record was not approached in the PRK treated eyes until a month after surgery.
Dr. Daniel Durrie, one of the study’s organizers and a leading proponent of Intralase SBK, has been quoted as saying, “The results for Intralase SBK just keep getting better. Our studies indicate so far that there is nothing to choose from between Intralase SBK and PRK in the long term, but the results with Intralase SBK come much sooner and with less pain.” (5)
Recovery Time
Patients undergoing Intralase SBK and Bladeless LASIK often have very brief recovery periods; typically these can be measured in hours rather than days.