Ординатура / Офтальмология / Английские материалы / LASIK and Beyond LASIK Wavefront Analysis and Customized Ablation_Boyd_2001

ring. During advancement, the current on the display should not exceed 80 milliamps (Figure 10-7). The instrument is now ready for surgery.

The Surgeon

Lasik should be performed in a sterile environment wearing cap, mask and boots. We prefer no-glove technique with a Betadine hand scrub between patients, drying with a lint free cloth.

SURGERY PREPARATION

Draping

Apply a disposable self-adhesive drape (fenestrated is easier to apply). Ask the patient to open both eyes as much as possible. To exclude the eyelashes from the operating field, have your assistant hold the drapes’ opposite corners as you apply the drape at the edge of the superior eyelid first and then do the same with the inferior eyelid. Make sure to include the lid margins in the adhesive backing of the drape so they will not be in the way of the microkeratome on course over the suction ring (Figure 10-8).

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Figure 10-9. Accommodate suction ring within the intrapalpebral opening.

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Speculum

A locking eyelid speculum is recommended, but either locking or non-locking speculum can be used. The ideal speculum should provide maximal patient comfort when fully opened, allow for temporal and superior approaches, accommodate suction ring within the intrapalpebral opening and maximize exposure to enable clear passage of microkeratome (Figure 10-9).

Figure 10-10. Prior to placing the LASIK suction ring, the head should be positioned so the chin and forehead are in the same frontal plane.

Positioning the Patient

Prior to placing the LASIK suction ring, the head should be positioned so the chin and forehead are in the same frontal plane (Figure 10-10). Make sure the amount of inferior and superior sclera’s are the same therefore the cornea is centered between the lids (Figure 10-9).

THE LASIK PROCEDURE

Marking

The cornea should be marked with a pararadial line that facilitates exact repositioning of the flap in case of a free cap. A minimum amount of gentian violet should be used to avoid epithelial toxicity.

Placement of the Suction Ring

The LASIK suction ring is placed slightly decentered 1 mm superiorly (Figure 10-11). Suction ring should be firmly placed on the globe with one hand and at the same time apply downward pressure on speculum to proptose the eye.

The vacuum pump is activated and the intraocular pressure is checked with a Barraquer tonometer lens to assure an intraocular pressure

LASIK SURGICAL TECHNIQUE

Figure 10-11. The LASIK suction ring is placed slightly decentered 1 mm superiorly.

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Figure 10-12. Confirming that the area of applanated cornea is Subjects Index the same side or smaller than the circular mark on the applanating

surface of the tonometer.

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greater than 65 mm Hg., confirming that the area of applanated cornea is the same side or smaller than the circular mark on the applanating surface of the tonometer (Figure 10-12). The tonometer and corneal surfaces should be dried to avoid a false reading. Many expert surgeons no longer perform tonometry, relying in digital touch, small displacements and observing the slight mydriasis induced by the suction itself. The surgeon should remember that re-

Figure 10-13. Loading the microkeratome.

dundant conjunctiva could produce the false sensation that the suction ring has adhered to the globe by obstructing the suction. It is very important to remember to keep the cornea wet at all times, and just dried prior to the tonometer reading, as it could result in a complication.

The Microkeratome Cut

When the above is satisfied the surgeon is ready to progress with the keratectomy. After loading the keratome onto the post of the suction ring press down on the motor to slightly compress the cornea and thereby fully seat the eye adapter before engagement of gear to the rack (Figures 10-13 and 10-14). Immediately prior to passage of the microkeratome, one or two drops of glycerin-based anesthetic (Proparacaine) are instilled over the surface of the cornea to allow the microkeratome to advance more smoothly. Make sure to apply the drops directly from the bottle and not through a cannula since the drop size vary and sometimes is not enough fluid to lubricate the cornea. Excess fluid should be removed using a Merocel sponge to prevent it from going into the gears of the microkeratome and then onto the mirrors of the laser consequently disturbing beam quality. Proparacaine is used rather than BSS in order to keep salts away from the microkeratome.

Figure 10-14. After loading the keratome onto the post of the suction ring press down on the motor to slightly compress the cornea and thereby fully seat the eye adapter before engagement

of gear to the rack.

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The keratome is placed into the suction ring and advanced by depressing the pedal. The microkeratome is reversed and the vacuum is stopped. The microkeratome and suction ring can be removed at the same time as a one unit (Figure 10-15).

Figure 10-16. The corneal flap is lifted superiorly with curved forceps

Figure 10-18. The laser focus is achieved over the pupillary center

Laser Ablation

Figure 10-17. The corneal flap is lifted superiorly with curved cannula.

Figure 10-19. The head is rotated to the right and the body to the left; as a result the ablation will be decentered.

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The corneal flap is lifted superiorly with curved forceps (Figures 10-16, 10-17), the laser focus is achieved over the pupillary center (Figure 10-18), and patient’s head is again aligned so the chin and forehead are in the same frontal plane; a straight imaginary line passes through the feet, umbilicus and nose (Figures 10-19 and 10-20). At this point, the surgeon can proceed with the ablation of stromal bed.

Figure 10-20. A straight imaginary line passes through the feet, umbilicus and nose

When the larger zones of ablation or astigmatism are being completed the surgeon must protect the hinge from ablation by holding a Merocel sponge over this area (Figures 10-21 and 10-22).

Replacing the Flap

When the ablation is complete, couple of drops of BSS is added onto the stromal bed and then the corneal flap is replaced using the cannula starting superiorly (Figures 10-23 and 10-24). Make sure the tip of the cannula is outside the flap before flap is positioned back because surgeon can either place a hole on the flap or scratch the stromal bed, especially when using sharp tips cannulas. (Figure 10-25 and 10-26) The cannula is placed underneath the

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Figure 10-25. Make sure the tip of the cannula is outside and parallel to the flap before flap is positioned back

Figure 10-26. Canulla is not parallel; surgeon can accidentally scratch the stromal bed

Figure 10-27. The cannula is placed underneath the flap and irrigation is completed to clear any remaining debris

Figure 10-28. BSS is use under the flap to facilitate “floating” back into its original position.

Figure 10-29. Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge.

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flap and irrigation is completed to clear any remaining debris from the interface as well as allowing BSS under the flap to facilitate “floating” back into its original position. (Figures 10-27 and 10-28)

The Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge (Figure 10-29).

The flap is inspected to reassure that there are no wrinkles and for proper position by making sure

Figure 10-30. The flap is inspected to reassure that there are no wrinkles and identical distance between the gutter and keratectomy edge is present.

an identical distance between the gutter and keratectomy edge is present all over the flap circumference (Figure 10-30). Depressing the peripheral “non flap” cornea with closed blunt 0.12 forceps completes a Slade’s striae test (Figure 10-31). When striae test is positive around the flap edge appropriate apposition has been achieved. During this phase it is recommended to keep a BSS drop over the central corneal epithelium to keep it wet. There is no specific waiting time with this technique, but we recommend waiting 3-5 minutes before removing the speculum. The case is completed by carefully removing the speculum. When doing this step, make sure to lift and close the speculum at the same time to avoid displacement of the flap.

The patient is then instructed to blink normally, and is observed through the microscope. The flap should remain in the same position and appear adhered to the cornea bed (Figure 10-32).

Figure 10-31. When striae test is positive around the flap edge appropriate apposition has been achieved.

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Figure 10-32. The patient is instructed to blink normally, and is observed through the microscope.

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Bleeding of peripheral corneal vessels usually occur in long-term contact lens wear patients. The occurrence is higher when we use the 9.5 Hansatome suction ring. We prevent this by using an 8.5 suction ring if we notice any limbal pannus in the slit lamp examination. We don’t use any drug to stop intraoperative bleeding, because some of them could

interfere with the iris, causing irregular dilation of the pupil. We use a Merocel sponge and apply some pressure on the peripheral vessels to stop the bleeding; generally is over by the time we finish the ablation treatment and reposition the flap (Figures 10-33 to 10-36)

Figure 10-33. The corneal flap is lifted superiorly with curved forceps

Figure 10-34. Merocel sponge is use to clean the corneal stromal bed

Figure 10-35. The laser focus is achieved over the pupillary center and the ablation start.

Inferior eyelashes bleeding is usually due a poor technique when loading the keratome; the surgeon is either applying to much pressure onto the suction ring and it end deeper than the speculum or not applying downward pressure on speculum to proptose the eye. (Figure 10-37)

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Figure 10-37. The surgeon is applying too much pressure onto the suction ring and it end deeper than the speculum.

HOME CARE INSTRUCTIONS

-Wear a clear eye shield to sleep for the first five days.

-Wear protective sunglasses anytime patient is outside for the first five days.

-Use Acular eye drops only on the first day post-op and only for discomfort.

-Two hours after surgery start 1 drop of Ocuflox and Lotemax every 3 hours while awake

-Patient should wait about one minute between drops.

-Make sure to shake the Lotemax before us-

ing.

-Next four days use Ocuflox and Lotemax four times a day.

-Patients may need Lubricating drops for dry

eyes.

-Do not to rub the eyes for 5 days after the surgery, avoid any trauma to the eyes.

-Patient may wash face, but avoid getting anything into the eyes.

-Use good hand washing technique and cleanliness.

-No eye makeup for 3 days -No swimming for 10 days

-Stay out of hot tubs for 4 weeks

-Patient may shower; however keep the force of the water away from the eyes

-We advice against driving

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LASIK surgery has become a quick, automated procedure. However, a good outcome still depends largely on the surgeon’s knowledge, skill, and experience. A successful procedure begins with appropriate patient selection and counseling. Intraoperatively, there must be great attention to detail. This chapter will describe surgical techniques designed to achieve the best outcomes and lowest risk of complications in LASIK surgery.

Patient Counseling

A successful LASIK surgery depends as much on a technically good operation as it does on an appropriately counseled patient. The patient must not only be informed of the risks and benefits of the procedures, but also its limitations. Thus, the patient must have realistic expectations of what the outcomes could be.

In counseling the patient, it is far better to counsel for lesser outcomes and have the patient pleasantly surprised than the converse. The goal of the surgery is functional vision without glasses or contact lenses. There can be no guarantee of 20/20 vision. The vast majority of the time, results will be excellent and the patient will be pleased.

Presbyopic patients should understand that reading glasses will still be needed after LASIK. For surgeons who aim for some initial overcorrection, the patient should also be forewarned about some difficulty with their intermediate range of vision as well. Myopic patients need to understand that their faces may be blurry in the mirror postoperatively. Hyperopic patients should be informed that they may be temporarily myopic.

The surgeon should explain that, particularly for the higher levels of correction, visual recovery may take several weeks to months. Although a big improvement in their uncorrected visual acuity will occur in the first 24 hours, continued improvement can occur after this. Additionally, patients should understand that 5-10% will require an enhancement to achieve the desired results. They should be given an estimate of the time at which this might occur, if desired, based upon their preoperative refractive error. We prefer to wait one month per diopter of myopia and three months per diopter of hyperopia prior to performing an enhancement.

Achieve Adequate Exposure

Achieving adequate exposure is the first and one of the most important steps of the LASIK procedure. All of the subsequent maneuvers in the surgery rely on this step. Adequate exposure is critical to visibility, achieving adequate suction, ability to place the microkeratome properly, unobstructed passage of the microkeratome, and a well-exposed stromal bed. There are certain orbital anatomies that predispose to difficult exposure and these should be noted preoperatively. Deep set orbits, prominent brows, or small palpebral fissures may all interfere with placement of instruments on the globe. In these instances, as well as others, it is often helpful to have the patient maintain a chin-up position for adequate visibility and instrument placement. If the patient has a prominent lower cheek that overhangs the lower blade of the speculum, the surgeon may use his/her 4th and 5th fingers to retract this tissue inferiorly and out of the surgical field. Similarly, a technician can

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