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

Chapter 45

Figure 45- 1: The two stab incisions are not radial; they are oriented parallel to the direction of lens insertion. The entry of the stab incision should be pointed directly towards the site on the iris where the enclavation will take place.

to 4 o’clock. The first two stab incisions are designed to permit the enclavation needle to enter the eye directed exactly to the spot where enclavation will take place (Figure 45-1).

Once the stab incisions are made, the anterior chamber is irrigated first with Miochol. Then it is filled with a cohesive viscoelastic such as Healon

or Amvisc Plus. A cohesive viscoelastic is very helpful in cases of phakic lens implantation, because it can be irrigated from the eye very easily at the end of the procedure (Figures 45-2,45-3).

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Figure 45-2: The miotic is injected into the eye. Notice that the needle is pointed directly towards the anticipated enclavation site.

Figure 45-3:After the pupil is constricted, a cohesive viscoelastic is injected into the anterior chamber. At the risk of some redundancy, notice again that the direction of the corneal incision is straight to the enclavation site and not radial.

Figure 45-4: The incision is constructed in two planes. The first plane is a groove of about one-half the corneal thickness.

Figure 45-5: The second plane is a short tunnel of roughly 1 mm to 2 mm. The groove and the tunnel are planned so that the external groove and the internal tunnel are in a line parallel to and slightly above the iris. This minimizes the likelihood of incision distortion and viscoelastic leakage.

The lens hook then rotates the lens perpendicular to the original incision. Using again the example of a 9 o’clock incision, the lens is placed in the eye initially from 9 o’clock to 3 o’clock. It is now rotated from 6 o’clock to 12 o’clock (Figures 45-6, 45-7).

The enclavation needle is slipped into the eye through one of the stab incisions before the lens forceps are passed through the primary incision. If these steps are reversed, it is common to see viscoelastic leakage at the primary incision when the enclavation

needle is placed. Therefore, the needle is always put in first.

The lens forceps hold the optic of the lens gently downward against the iris while the first enclavation takes place. The enclavation needle pushes down and forward against the iris, gathering a knuckle of iris in front of it. The enclavation needle is then lifted into the claw, scooping iris with it in a single, easy motion. If the amount of iris secured in the claw is insufficient, the enclavation can be re-

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Section 4

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Section 6

Section 7

Subjects Index

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Figure 45-6: The intraocular lens is placed in the anterior chamber and left there until after the incision has been sutured and the anterior chamber controlled.

Figure 45-7: Alens hook is used to rotate the lens perpendicular to the direction of insertion. For example, for a temporal incision in the right eye, the lens was inserted from 9:00 towards 3:00. Now it is rotated from 12:00 to 6:00.

Figure 45-8: The enclavation is always difficult to capsule for demonstration. The lens is held with the forceps and the enclavation needle gathers the iris. In this view the tip of the needle is pushing down and forward against the iris, gathering a fold in front, in much the way a snowplow pushes snow.

peated until a sufficient amount of iris is captured (Figures 45-8, 45-9).

Typically, at this point a little more viscoelastic is placed in the eye to deepen the chamber and again to push the lens against the iris. The last step is repeated, this time using the second stab incision to

Figure 45-10: The iridotomy is made by gathering some iris with the tip of sharp scissors, just like the enclavation needle gathered some iris for the enclavation. The scissors are twisted so that the iris lifts away from the crystalline lens. The scissors are closed, making a snip iridotomy.The tips can be opened within the iridotomy to make it larger if needed.

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Figure 45-11: Aclose-up of an enclavation showing an adequate amount of iris captured in the claws.

Figure 45-12: The completed case, with the lens centered, adequate enclavations, and an iridotomy.

A small peripheral iridectomy or iridotomy must be performed. The easiest method is to slip very small, very sharp scissors into the anterior chamber and use one tip of the scissor to capture and lift a piece of iris. When the scissors close, they snip a piece of the iris, forming an iridotomy. If necessary, the tips of the scissors can be placed in the small iridotomy and opened to enlarge the opening (Figure 45-10).

Figure 45-13: The lashes of the lateral upper eyelid are draped because they could interfere with the movement of the microkeratome.

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Figure 45-14: The Moria suction ring is placed on the eye, centered, and activated with high vacuum in preparation for making the flap.

Figure 45-15: The flap is made with the forward pass of the microkeratome while the ring is on high vacuum. When the head reaches its stop, the motor is inactivated and the vacuum is reduced to its low setting before the head is retracted. Retraction under low vacuum reduces epithelial friction and abrasions.

the ring except where the flap will rest when flipped. I used to dry everywhere but once I lost suction and the ring moved. The flap was stuck to the dried ring and ripped off the eye, leaving a free cap (Figure 45-16).

The tip of a second sponge is used to lift the flap and flip it over. That same sponge is immedi-

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Figure 45-17: Stage one of lifting the flap with the cellulose sponge. A new, dry sponge is used as a pusher, engaging the flap at its temporal edge.

Figure 45-18: Stage two of lifting the flap with the cellulose sponge. The tip of the sponge pushes the flap and begins to flip it over.

Figure 45-19: Stage three of lifting the flap with the cellulose sponge. The flap is completely lifted and flipped. The sponge smoothes out the flap to prevent wrinkles.

After the ablation the corneal bed and the underside of the flap are irrigated vigorously with balanced salt solution and wiped thoroughly with the cellulose sponge. After I am confident that both surfaces are completely clean and free of debris, the same

Figure 45-20: The same sponge is immediately used to dry any moisture that may have settled on the stromal bed.

sponge is used to reposition the flap. The surface of the flap is massaged several times with the lint-free sponge to remove underlying fluid, the gutters are dried, and the flap is allowed to seal in place (Figures 45-22 -- 45-25).

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Section 6

Section 7

Subjects Index

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Figure 45-21: Stage three of lifting the flap with the cellulose sponge. The flap is completely lifted and flipped. The sponge smoothes out the flap to prevent wrinkles.

Figure 45-22: Once the ablation is completed, the assistant irrigates the bed and the underside of the flap vigorously with BSS, while the surgeon scrubs each with the cellulose sponge.

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Results

Following surgery, the postoperative uncorrected visual acuities were very similar. 43% of the LASIK patients and 50% of the Artisan patients saw 20/20 or better without correction. A total of 68% of the LASIK patients and 66% of the Artisan patients saw 20/25 or better, and 88% of the LASIK patients and 94% of the Artisan patients saw 20/40 or better. The trend toward improved vision in the Artisan patients had mild statistical significance (p=0.04), but the difference between the two is still very slight (Table 2, Graph 2).

There is, however, a tremendous difference in the postoperative BCVA between the two treatment groups. Sixty-three percent of the LASIK group and 94% of the Artisan implant group were able to see 20/20 or better with correction following surgery. All of the Artisan patients saw at least 20/25 or better. However, only 84% of the LASIK patients saw 20/25, and only 97% of them saw 20/40. This represents a dramatic shift from the BCVA prior to surgery, where the LASIK patients clearly had the advantage. Postoperatively, the advantage shifted to the Artisan lens patients. This is statistically significant to the level of p=0.0001 (Table 3, Graph 3).

Table 2

Table 3

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Subjects Index

The average visual acuity in the LASIK group fell slightly, from 20/21 to 20/24, while in the Artisan lens group it improved slightly from 20/24 to 20/18 (Table 4).

In the Artisan lens group, there was a dramatic improvement in the number of eyes that gained BCVA. Thirteen percent of the LASIK eyes improved by one or more lines of visual acuity, and only 2% improved by two lines of vision or more. On the other hand, 83% of the Artisan patients improved by one or more lines, and 22% of the eyes improved by two or more lines (Table 5).

Just the reverse was found when we examined loss of BCVA. None of the Artisan implant eyes lost any visual acuity; however, 25% of the LASIK eyes lost one or more lines, and 6% lost two or more lines of BCVA. In many cases, the recorded loss of one line occurred because some patients before surgery were examined while wearing a hard contact lens, whereas they were examined behind the phoropter postoperatively. This variable applied to Artisan lens patients as well. There was no question that the Artisan lens eyes gained more vision and lost no vision, while the LASIK eyes gained only a little vision and lost some as well (Table 6).