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LASIK-Basics and Microkeratome Theory

LASIK-Basics and Microkeratome Theory. Dr. Rupal Shah LASIK India , LASIK Information India , Blade Free LASIK India New Vision Laser Centers. LASIK. “Laser In Situ Keratameleusis” Followed from the procedure known as ALK or MLK Basic theory is decades old.

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LASIK-Basics and Microkeratome Theory

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  1. LASIK-Basics and Microkeratome Theory Dr. Rupal Shah LASIK India, LASIK Information India, Blade Free LASIK India New Vision Laser Centers New Vision Laser Centers

  2. LASIK • “Laser In Situ Keratameleusis” • Followed from the procedure known as ALK or MLK • Basic theory is decades old New Vision Laser Centers

  3. Automated Lamellar Keratomeleusis(ALK) • Consists of two incisions • First, a slice of cornea 160 microns thick and a diameter of 8 mm is removed • Second, a thin slice of cornea corresponding to the refractive error is removed • The first slice is replaced back New Vision Laser Centers

  4. Problems with ALK • There are limits to the accuracy of a mechanical instrument • The second slice could never be accurate or precise enough to compete with other forms of refractive surgery New Vision Laser Centers

  5. Excimer Laser • Can ablate tissue with great accuracy • Since the first cut is not critical, that is done with the microkeratome • The refractive lenticle is removed with the excimer laser • Refractive change can occur with the excimer laser without disturbing the epithelium New Vision Laser Centers

  6. LASIK-Technique • The microkeratome makes a horizontal cut on the cornea • Slice is not excised completely • A tongue like flap is removed to one side • The laser is applied in the usual manner • The flap is replaced and sticks in place New Vision Laser Centers

  7. Horizontal-First Cut New Vision Laser Centers

  8. Horizontal-First Cut New Vision Laser Centers

  9. Horizontal-First Cut New Vision Laser Centers

  10. Flap is lifted to a side New Vision Laser Centers

  11. Laser is applied under the flap New Vision Laser Centers

  12. Flap is replaced New Vision Laser Centers

  13. Microkeratomes-History • Basic Theory was evolved by Jose Barraquer decades ago • First Used for ALK/MLK • In the 90’s, modified for use in the procedure that has come to be known as LASIK New Vision Laser Centers

  14. Used for making thin lamellar slices of the cornea Microkeratomes New Vision Laser Centers

  15. Microkeratomes Used in LASIK • Capable of creating thin lamellar slices of the cornea of fixed or adjustable depth • The Slice interface should be smooth, and free of spherical aberrations • The slice should have an appropriate diameter along with an appropriate hinge size. New Vision Laser Centers

  16. Principle of Microkeratomes • Work on the principle of a carpenter’s plane or ‘randho’ • The blade is at a fixed distance from an applanation plate, which determines the thickness of the slice Blade Plane Blade to Plate Gap New Vision Laser Centers

  17. FLAP CREATION New Vision Laser Centers

  18. Problem of applanation • The cornea is a spherical object, and unlike wood, will not be in contact with the applanation plate at all or any points along the blade motion • Therefore, very high suction is applied all around the cornea, to ensure high IOP, and thereby pressure of the cornea against the applanation plate New Vision Laser Centers

  19. SUCTION and IOP • The suction ring will induce a rise in intraocular pressure. • An adequate vacuum will induce pressure greater than 65mm Hg, which is the recommended minimum requirement. • Insufficient vacuum will not provide the optimum positioning of the eye within the suction ring. If this occurs, an irregular flap may be produced. New Vision Laser Centers

  20. First Component of a Microkeratome • A Suction ring and a vacuum pump, to ensure adequate applanation of the cornea by the applanation plate • If the cornea is not applanated perfectly, we would get thin flaps, no flap or a small free lamella of the cornea Plate Blade New Vision Laser Centers

  21. RING SELECTION • 8.5 mm ring • Steep corneas (K > 45), thinner flaps • Small diameter corneas (prevent dissection of blood vessels) • 8.8 mm ring • 9.0 mm ring • Standard myopic ring • 9.5 mm ring • 10.0 mm ring • All hyperopes and flat corneas (K < 40) • Extremely steep corneas (K > 47) New Vision Laser Centers

  22. RING SELECTION • Ring selection closely corresponds to the desired flap diameter • Slightly larger with steeper K’s • Slightly smaller with flatter K’s New Vision Laser Centers

  23. Second Component • A means to arrive at a conclusion whether there is sufficient applanation or not • Indirect Way: Through an applanation tonometer, measuring IOP • Direct Way: Through a transparent applanation plate New Vision Laser Centers

  24. APPLANATOR • The applanators are used to verify the cut diameter prior to flap creation. • The applanator does not replace, or function as a tonometer. • Diameter check vs. pressure check • IOP measurement is recommended for every eye prior to flap creation New Vision Laser Centers

  25. Applanation of the Cornea New Vision Laser Centers

  26. Flap Interface Should be Smooth • An ordinary knife would lead to lot of scarring on the cornea • A special blade is used which oscillates at a high speed to and fro in the direction orthogonal to the direction of forward motion • Higher the oscillation speed, the smoother is the cut New Vision Laser Centers

  27. Oscillation of the blade • A rotating shaft with an eccentric tip is used. The shaft is rotated by a turbine motor, either gas driven (faster oscillation) or electrically driven New Vision Laser Centers

  28. Third Component • A means of forward translation of the blade, along with oscillation in an orthogonal direction • Forward Motion should be smooth, uniform and independent of load • Can be done by hand (manual machines), a cable drive or gears New Vision Laser Centers

  29. FLAP FACTORS • BLADE SPEED (12,000 rpm) • BLADE ANGLE AND SHARPNESS (25 degrees) • SPEED OF TRANSITION ACROSS THE CORNEA (4.0 mm/sec) • DISTANCE BETWEEN THE BLADE AND THE PLATE • IOP (>65mmHg) • PRESSURE DURING TRANSITION • NASAL DECENTERING (0.5mm) New Vision Laser Centers

  30. FLAP FACTORS • Pressure exerted by the surgeons hands on the instrument during the surgery could effect the outcome of the procedure. • Too much downward pressure will create a thicker flap. • Not enough downward pressure, a thin flap or loss of suction may occur. • The weight of the keratome has been adapted to the speed of the keratome head across the cornea. New Vision Laser Centers

  31. Cable Drives for rotational and axial motion New Vision Laser Centers

  32. Fourth Component • The thickness of the flap is determined by the blade to plate gap • This gap can be varied by physically increasing the gap, or by using different thickness applanation plates New Vision Laser Centers

  33. HEADS • Stainless Steel Construction • Available in multiple depths: • 130 µm • Thin corneas (500u – 530u), high myopes • 160 µm • Moderate corneas (530u – 560u) • 180 µm • All thick corneas (>560 µm) New Vision Laser Centers

  34. Four Essential Components • Suction ring and Vacuum pump • Applanation plate with means of checking applanation • A means of oscillating the blade at high speed and a mechanism for forward translation of the blade • An adjustable plate to blade gap New Vision Laser Centers

  35. HANDPIECE Fully assembled, no on eye assembly required New Vision Laser Centers

  36. CONSOLE Blade Change Vacuum Level Test Vacuum Adjust Battery Indicator On/Off Pedal Connect Handpiece Connect Vacuum Port New Vision Laser Centers

  37. Other Microkeratomes • Suction Ring is first applied on the eye. • The Handpiece is then placed later New Vision Laser Centers

  38. New Vision Laser Centers

  39. FLAP FACTORS • Your success is dependent on close attention to detailed: • assembly • operation • maintenance • The device is a precisely manufactured instrument designed to cut precise corneal lenticules. Damage to any part of the instrument may lead to undesired results New Vision Laser Centers

  40. CLEANING • Always follow the recommended cleaning regimen • Failure to use the proper cleaning technique or cleaning agents may: • Damage the components • Lead to undesired clinical outcomes New Vision Laser Centers

  41. Laser Microkeratomes • Intralase, Femtec 20/20 • All laser procedure • Uses Photodisruption New Vision Laser Centers

  42. New Vision Laser Centers

  43. Thank You Rotational Cable App.Plate Axial Cable HingeStop Blade Suction Ring New Vision Laser Centers

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