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

Figure 7-3: Blade cover opened. This way one does not damage the blade

Figure 7-4: Blade being inserted into the groove of the microkeratome’s head

Figure 7-5: Hansatome head showing l for left eye

Figure 7-6: Hansatome head showing the 180 & 160 micron thickness marks

The head can be 180 or 160 microns (Figure 7-6). This means that if we use the 180-micron head the microkeratome will create a flap of 180 microns and if we use the 160-micron head the flap thickness will be 160 microns.

Once the head & the adapter are fixed (Figure 7-7) the motor of the keratome is taken and screwed onto the head of the microkeratome (Figures 7-8 and 7-9). The cord is connected to the motor, which in turn is connected to the power supply. Once the motor has been screwed into place, the blade will swing from right to left with a slow regular

Figure 7-8: Motor of the microkeratome being screwed onto the head.

Figure 7-7: Head fixed on the adapter.

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Figure 7-9: Microkeratome head fixed on the suction ring.

Chapter 7

Figure 7-10: Head moving on the tracks of the suction ring.

gear tooth of the rack. While lightly supporting the motor, press the forward pedal (labeled F) of the motor foot switch to start the head across the ring (Figure 7-10). In normal operation, the head will automatically stop, with two audible beeps. This will happen when the head reaches the mechanical stop and the motor current will drop to zero. Once this happens, depress the reverse pedal (labeled R) of the motor foot switch to reverse the head back off the ring. If everything is alright then only should one proceed with using the Hansatome on the patient.

Care & Maintenance

The mechanical components of the Hansatome should be cleaned immediately and thoroughly after each use. Delayed cleaning can leave residual debris such as stromal cells, epithelial cells and strands from surgical sponges. If the components are autoclaved, this debris may become firmly baked onto the com-

ponents. To remove debris allow the components to soak in very hot distilled water for a minimum of 15 minutes, then employ the cleaning regimen outlined below and repeat until all debris has been removed. Debris allowed to build up on the Hansatome Microkeratome components may affect the performance of the device and result in malfunction of the device and possible patient injury.

Chiron Vision recommends use of a cleaning solution consisting of 2 parts green Palmolive dishwashing liquid (unconcentrated product) to 100 parts warm tap water. Do not substitute. The cleaning solution used must not leave any residue. All the components must be thoroughly rinsed with distilled or sterile water after cleaning in the solution. Once this is done one should dry with a lint-free surgical wipe or blow dry with microfiltered forced air. Since most of the components are small and could possible be lost in a sink or drain, it is best to perform the cleaning procedure by using small bowls or basins. The bowls or basins should be made of plastic and not metal to avoid potential damage to the Chiron Vision Hansatome microkeratome mechanical components.

For cleaning the Hansatome motor, wipe the outside of the motor housing with a cloth dampened with isopropyl alcohol and clean the motor shaft with a dry toothbrush. Do not immerse it in any fluid. Do not use ethylene oxide sterilization for the motor as this can congeal the internal grease and cause potential malfunctions.

For cleaning the cord, one should wipe it with a cloth dampened with isopropyl alcohol. Do not immerse it in any fluid or autoclave it. Autoclaving will cause convolution of the initially round cable and will cause cumulative damage to the cable and electrical connectors, eventually leading to possible malfunction.

Contents

Section 1

Section 2

Section 3

Section 4

Section 5

Section 6

Section 7

Subjects Index

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Contents

Section 1

Section 2

Section 3

Section 4

Section 5

Section 6

Section 7

Subjects Index

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Troubleshooting

Head will not Advance Across the Suction Ring

The head may be jammed on the first tooth of the gear track. Press the reverse pedal of the motor foot switch to release, then place the head in position and try again.

Head will not Fit Properly Onto the Suction Ring

Confirm that the left/right eye adapter has been oriented correctly onto the head for the eye to be operated on. Confirm that the head has been oriented near the correct starting point for the cut, at which point the adapter should drop down onto the pivot pin. Check for any obstructions or debris that may be impeding the loading of the head onto the suction ring. Clean the head, adapter and suction ring and try again.

No Suction Occurring

Check if the tubing is all right or if the attachment of the tubing to the power supply is correctly done.

SURGICAL TECHNIQUE

The surgical technique of Down Up Lasik starts from draping of the patient. When one drapes the patient one should be careful that the eyelashes do not come into the microkeratome. The authors use a cellotape to tape the eyelashes so that they are away from the field of the microkeratome. Then the eyelid speculum is inserted. The eyelid speculum should be a good one, which retracts the eyelids well.

Once the eyelid speculum is inserted, one should check the working of the microkeratome. The microkeratome head should be fixed on the suction ring and the movement of the microkeratome checked. One should check that the microkeratome moves smoothly on the tracks of the suction ring.

Using the reference marker (Figure 7-11) a mark is made on the cornea. Then the suction ring is

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taken and placed properly on the eye (Figure 7-12). Once the suction ring is fixed in the proper position the foot switch of the vacuum is pressed so that the suction comes on. The tracks of the suction ring should be placed nasally. Once the suction is on one should check the intraocular pressure of the eye using the Barraquer´s pre-surgical tonometer. This creates a black ring in the center. The black ring should be smaller than the white ring seen in the Barraquer’s

Figure 7-13: Flap being lifted with a spatula

tonometer. If this happens, then the intraocular pressure is greater than 65 mm of Hg and the case can be proceeded with. If it is larger than the white ring then something is wrong with the suction. So release the suction and start the process once again. Once everything is alright swab the area so that excess fluid is not present.

When the suction ring is fixed in position, the microkeratome head is now fixed onto the pin of the suction ring. There are notches on the pin of the suction ring, which coincide with the head so that the head gets properly fixed. Then the forward foot switch is depressed and the microkeratome moves on the tracks of the suction ring. This will automatically stop when the head hits the stop mechanism. When this happens two beeps will be heard. Then press the reverse foot switch and the head will move in the reverse direction. Once it has come back fully release the suction and take off both the suction ring and the microkeratome head.

Use a fine spatula or repositor and lift the flap from the inferior area (Figure 7-13). Lift the flap so that the hinge is superior and the flap lies superiorly (Figure 7-14). Before the whole Lasik procedure was started one should have calibrated the excimer laser machine and the required refractive power entered. The authors use a Chiron 217 excimer laser machine and overcorrect by 10%. The ablation is then started

Figure 7-14: Superior flap made.

(Figure 7-15). One can use an eye tracking system or alternatively fixate the eye with a forceps and start the ablation. One should be careful that decentered ablation does not occur. See to it that the excimer laser hits perpendicular to the cornea and not obliquely. The laser should hit the pupillary area. In cases of astigmatism one should be careful that the eye is not rotated otherwise the axis of the astigmatism will become different.

When the ablation of the excimer is completed, one should wash the stroma with the irrigating fluid (BSS). Wash the flap well. See to it that there is no foreign body lying on the stroma. Take a wet Merocel sponge (Figure 7-16) and clean the flap with both ends of the sponge. This will prevent epithelial ingrowths. Then take the syringe with BSS and pass the cannula under the flap. While irrigating lift the flap and the flap will fall back into its original position onto the stroma. One can use a spatula also to reposit the flap (Figure 7-17). Once the flap has been repositioned check that the reference marks coincide (Figure 7-18). Then wait for a couple of minutes so that the flap is stuck. Carefully take out the speculum without disturbing the flap.

The authors see the patient on the slit lamp after half an hour and if everything is all right the patient goes home without a patch. Both eyes are done simultaneously. The patient is put on artificial

Contents

Section 1

Section 2

Section 3

Section 4

Section 5

Section 6

Section 7

Subjects Index

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Figure 7-15: Excimer ablations started

Figure 7-17: Superior flap reposited with a spatula. One can use an irrigating cannula to do the same thing

tears; antibiotic and steroid drops for 2-3 weeks only. The patient is seen again the next day. When seen on the slit lamp it should be as if no treatment was done, except for slight subconjunctival hemorrhages due to the suction ring being present. The patient is seen again after a month and if necessary relasik is done by lifting the flap. This is done if regression has occurred. In such cases one need not again make the cut, but lift the same flap back.

Figure 7-16: Flap cleaned with a merocel sponge. This helps prevent epithelial ingrowths.

Contents

Section 1

Section 2

Section 3

Section 4

Section 5

Section 6

Section 7

Subjects Index

Figure 7-18: Flap back in position. Note the cut edges of the flap. The reference markers should coincide

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FACTORS RESPONSIBLE FOR SECURING THE FLAP

There are basically four factors (3) responsible for securing the flap in position.

1. The natural capillary attraction of the tissues and mucoproteins. This occurs rapidly within seconds to minutes

1. The endothelial pump action. This occurs within minutes to hours.

3.Epithelial covering along the margin starts from 12-24 hours and

4.Scarring along the cut edge of Bowman’s layer occurs weeks to months later.

ADVANTAGES

The main advantage of the Down Up Lasik technique is that as the eyelid moves downwards it presses on the flap which has a superior hinge and thus does not displace the flap. The same does not apply to a flap, which has a hinge nasally. Gravitational forces also help in positioning the flap properly. The compression effect of the eyelid also helps to smoothen the flap. Another advantage of the Down Up Lasik technique is that it creates a large flap. The ablation pattern of the excimer requires a large flap preferably in cases of hyperopia treatment. Further chances of the flap getting shot with the excimer do not occur with the Down Up Lasik. Free caps do not occur with the Hansatome.

DISADVANTAGES

There are disadvantages of the Down Up Lasik technique also. One problem is the large flap. If the patient is wearing contact lenses they can have peripheral vascularization of the cornea. On cutting the cornea, as the flap is large these blood vessels bleed and it takes some time for the bleeding to stop. Another problem with the Hansatome is that the palpebral fissure should be large. If the fissure is small then the suction ring of the Hansatome does not fir in the eye and one would have to resort to a canthotomy. In such cases, the authors prefer to use the Automatic corneal shaper. Yet another problem with the Hansatome is that when the cut has been completed the suction ring and the keratome head are removed so that when the laser is being applied there is nothing to stabilize the eye. One can use the eye tracking system to get accurate ablation. The advantage of the Automatic Corneal Shaper in contrast is that once the keratome cuts the cornea the suction ring is not removed and this can stabilize the eye well. The suction is not stopped till the entire ablation is completed. One can move the eye is such a way as the suction is still on so that the excimer

DOWN UP LASIK

lasers are perpendicular to the cornea thus preventing decentered ablations. This is not possible with the Hansatome.

REFERENCES

1. Chiron Vision Hansatome Microkeratome operator’s manual

2.Lucio Buratto: Down Up Lasik with the new Chiron Microkeratome; Milano, Italy 1997

3.Jeffery J Machat: Excimer Laser Refractive Surgery: Slack Incorporated 1996.

Contents

Section 1

Section 2

T. Agarwal

Dr. Agarwal’s Eye Hospital Section 3

Chennai, India; Bangalore, India; Dubai

Section 4

Section 5

Section 6

Section 7

• Part of the text and some of the figures of this Chapter are Subjects Index presented with permission from Agarwal et al textbook on

REFRACTIVE SURGERY published by Jaypee, India, 1999.

•The authors are grateful to Bausch and Lomb for supplying some of the photos and materials for this Chapter.

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Introduction

This chapter will describe the basic steps in a LASIK procedure using the Pulsion FS Laser to create the corneal flap and the Bausch & Lomb Technolas 217 excimer laser (Figure 8-1). Today, more than a million refractive surgery procedures are performed in United States and LASIK has clearly become the number one choice. The quick visual recovery produced by LASIK makes the surgery very attractive; in addition it is currently the most sophisticated procedure to correct refractive errors.

The majority of complication in LASIK are related to the mechanical microkeratome; which use a metal blade to cut the cornea and create a flap. Even in the most expert surgeons hands complications occurs. It is very important that the corneal flap be the optimal diameter, thickness and quality to reproduce excellent short and long-term results. When using microkeratomes, the laser treatment cannot continue if a partial resection has been made, and the procedure must be postponed for usually 3 months. Should an interruption occur during the Pulsion FS laser procedure, we would ask the patient to wait for 45 minutes and then repeat the procedure to create flap.

The corneal flap is created under very low vacuum, delivering the laser energy directly to the middle layer of the cornea through a disposable glass lens. There is no trauma to the epithelial surface of the cornea, and the surgery is painless.

Patient Selection

Selection criteria for flap creation with the Pulsion FS Laser are the same that we use of traditional LASIK procedures. Patients should have a

Figure 8-2: The Pulsion FS Laser provides the surgeon with control of surgical parameters like Hinge angle, Hinge position, Flap diameter, and Flap position, Flap Thickness.

thetic (Proparacaine) should be instilled and then one more drop before the keratectomy. No preoperative miotic is used. The patient eye is prepared by irrigating the conjunctival fornices with an irrigating solution (Sterile Eye Wash Optopics) to clear the area of any secretions or debris. Swab the skin of the eyelids with a povidine-iodine swab stick and gently dry.

Surgical Logistics

The Pulsion FS Laser is an intrastromal scanning laser with a 3 micron spot size that can create a corneal flap with optimal accuracy and precision. Uti-

lizing a fraction of the energy of an Excimer laser, the femtosecond laser technology provides the surgeon with control of the following surgical parameters (Figure 8-2):

Hinge angle

Hinge position (temporal, nasal, superior) Flap diameter (mm) 8.0, 8.5, 9.0, 9.5 Flap position (superior, inferior, nasal or

temporal)

Flap Thickness (um) 150,160, 170, 180

The laser pulses are placed very closely together in a spiral pattern, and an uncut section of tissue is pre-programmed to create the hinge for the flap (Figures 8-3, 8-4, 8-5 and 8-6)

The laser flap procedure offers a very safe and predictable alternative to the traditional microkeratome approach. The Pulsion FS laser is an extremely clean and efficient solid-state laser, which means it does not rely upon a mixture of gases to generate a homogeneous beam, as does the excimer laser.

Draping and Speculum

-Proparacaine drops to lubricate. Place drape over the eyelashes.

-Continue with the lid speculum and open the lids to a comfortable position

-Confirm laser is in its Home position and align patient comfortably underneath.

-Lock patient bed in place.

Contents

Section 1

Section 2

Section 3

Section 4

Section 5

Section 6

Section 7

Subjects Index

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