**4.7 Using air for DM detachment in performing DALK**

Anwar and Teichmann introduced the big-bubble technique for performing DALK (Anwar & Teichmann, 2002). The technique is a fast method for separating the DM from corneal stroma. The air is injected in the deep layers of the corneal stromal tissues after a partialthickness trephination cut of about 60% to 80% of the corneal thickness. In most cases a big bubble is formed at the DM—stroma interface and a circular white outline demarcates the borders of the air bubble. The overlying corneal tissues are removed to expose the DM and provide the recipient bed for performing MD–ALK. This technique is used by many corneal surgeons throughout the world for performing DALK.

Large-bubble modified technique for performing DALK was introduced in 2010 (Behrooz & Daneshgar, 2010). The rationale of this technique was to create an air bubble at the DM stroma interface that was larger than the trephination wound so that total removal of the corneal stromal tissues could be accomplished with scissors to perform the TALK procedure. The "expanding-bubble modification of the big-bubble technique" (Daneshgar & Fallahtafti, 2011) is the method that I believe is useful for providing full exposure of the DM and performing TALK. The procedure is performed as follows:

A partial-thickness trephination to a depth of about 60% to 80% of the corneal thickness is performed as described in the big-bubble technique (Anwar & Teichmann, 2002). The center of the pupil is determined as the center of trephination using an 8- to 8.25- calibrated trephine (Katena Products, Denville, NJ) for an average cornea (Figures 2 and 3).

Fig. 2. Center of the pupil is considered as the center for trephination cut. Note that the pupil is dilated due to the injection of retrobulbar anesthetic solution.

fibers from underlying DM. John used indocyanine green and forced hydrodissection for performing TALK (John, 2004). This technique benefits from both hydrating the collagen fibers to create stromal swelling for introducing spatulas into the stromal tissues safely and

Anwar and Teichmann introduced the big-bubble technique for performing DALK (Anwar & Teichmann, 2002). The technique is a fast method for separating the DM from corneal stroma. The air is injected in the deep layers of the corneal stromal tissues after a partialthickness trephination cut of about 60% to 80% of the corneal thickness. In most cases a big bubble is formed at the DM—stroma interface and a circular white outline demarcates the borders of the air bubble. The overlying corneal tissues are removed to expose the DM and provide the recipient bed for performing MD–ALK. This technique is used by many corneal

Large-bubble modified technique for performing DALK was introduced in 2010 (Behrooz & Daneshgar, 2010). The rationale of this technique was to create an air bubble at the DM stroma interface that was larger than the trephination wound so that total removal of the corneal stromal tissues could be accomplished with scissors to perform the TALK procedure. The "expanding-bubble modification of the big-bubble technique" (Daneshgar & Fallahtafti, 2011) is the method that I believe is useful for providing full exposure of the DM

A partial-thickness trephination to a depth of about 60% to 80% of the corneal thickness is performed as described in the big-bubble technique (Anwar & Teichmann, 2002). The center of the pupil is determined as the center of trephination using an 8- to 8.25- calibrated

trephine (Katena Products, Denville, NJ) for an average cornea (Figures 2 and 3).

Fig. 2. Center of the pupil is considered as the center for trephination cut. Note that the

pupil is dilated due to the injection of retrobulbar anesthetic solution.

using dye for discriminating the stromal fibers from the underlying DM.

**4.7 Using air for DM detachment in performing DALK** 

surgeons throughout the world for performing DALK.

and performing TALK. The procedure is performed as follows:

Fig. 3. Depth of the trephination wound is checked using a fine toothed forceps.

Fig. 4. Sunny side up sign, red arrows point at a circular furrow encircling the air bubble at the DM\_ stroma interface.

A 27-gauge needle attached to an air-filled syringe is inserted bevel down into the deep stroma in the paracentral cornea as in the big-bubble technique. After air is injected, a paracentesis wound is performed using a stab knife (Eagle Laboratories, Rancho Cucamonga, CA) in a semivertical direction to drain aqueous fluid. A crescent blade (Eagle Laboratories) is used to excise emphysematous stromal tissues as in lamellar keratectomy. The paracentesis wound is widened to 3 mm with the stab knife and the posterior lip of the wound is depressed to drain some aqueous fluid to make the anterior chamber obviously hypotensive. A dry Weck-Cel® sponge is used to depress the cornea. When a big bubble

Manual Deep Anterior Lamellar Keratoplasty 63

Fig. 7. Green arrows point at the hydrated area in the corneal stromal bed.

Fig. 8. The bubble is expanded by injecting viscoelastic material into the bubble cavity. Viscoelastic injection is discontinued and the needle is withdrawn when the demarcating

furrow reaches the trephination wound circumference.

forms, the outline of the bubble is obviously seen as a circular furrow around a domeshaped elevation in the center, similar to the yolk of a sunny-side up egg (Figure 4).

This sunny-side up sign is useful for determining the presence and extent of the air bubble. The diameter of the bubble can easily be measured using calipers. In most instances the diameter of the bubble is about 6 to 7 mm and the border of the air bubble coincides with the trephination wound inferiorly and lies within about 2 mm inside the trephination wound superiorly (Figure 4). It may also be smaller in size, usually when repeated attempts at air injection have been needed (Figure 5),

It may form eccentrically as the bubble border extends beyond the trephination wound over a specific area and lies within the trephination wound in some other area (Figure 6).

Fig. 5. Sunny side up sign with a small egg yoke.

Fig. 6. Eccentric big-bubble. The air bubble extends beyond the trephination wound inferiorly. Red Arrows point at the boundries of the big-bubble.

forms, the outline of the bubble is obviously seen as a circular furrow around a dome-

This sunny-side up sign is useful for determining the presence and extent of the air bubble. The diameter of the bubble can easily be measured using calipers. In most instances the diameter of the bubble is about 6 to 7 mm and the border of the air bubble coincides with the trephination wound inferiorly and lies within about 2 mm inside the trephination wound superiorly (Figure 4). It may also be smaller in size, usually when repeated attempts

It may form eccentrically as the bubble border extends beyond the trephination wound over

shaped elevation in the center, similar to the yolk of a sunny-side up egg (Figure 4).

a specific area and lies within the trephination wound in some other area (Figure 6).

Fig. 6. Eccentric big-bubble. The air bubble extends beyond the trephination wound

inferiorly. Red Arrows point at the boundries of the big-bubble.

at air injection have been needed (Figure 5),

Fig. 5. Sunny side up sign with a small egg yoke.

Fig. 7. Green arrows point at the hydrated area in the corneal stromal bed.

Fig. 8. The bubble is expanded by injecting viscoelastic material into the bubble cavity. Viscoelastic injection is discontinued and the needle is withdrawn when the demarcating furrow reaches the trephination wound circumference.

Manual Deep Anterior Lamellar Keratoplasty 65

Fig. 10. Anterior wall of the bubble is incised using a stab knife.

Fig. 11. Anterior wall of the bubble is excised using blunt tip curved scissors along the trephination wound circumference leaving no corneal stromal tissues within the

trephination wound area.

When no big bubble is formed, the procedure is continued by hydrating a localized area in the stroma with BSS. There is no need for introducing a needle into the corneal stromal tissues for hydrating the collagen fibers; instead we can use a blunt-tipped cannula attached to a syringe filled with BSS to hydrate the stromal tissues by putting the blunt tip in close contact with the stromal tissues in a perpendicular direction and injecting fluid while depressing the tissues by the tip of the cannula (Figure 7). Air injection is repeated in the hydrated area using the same 27-gauge needle and an air-filled syringe. After the sunnyside up sign is seen, the 27-gauge needle used for air injection is attached to a syringe containing viscoelastic material (Coatel™; Bausch & Lomb, Madison, NJ). Viscoelastic material is injected while the needle is inserted into the bubble cavity in the horizontal direction with a rapid movement.

The injection of the viscoelastic material into the bubble cavity is continued slowly as the "egg yolk" is expanded slowly (Figures 8-9).

Fig. 9. Viscoelastic material is injected into the bubble cavity.

Care must be taken not to depress the cornea while injecting the viscoelastic material or to overexpand the bubble beyond the trephination wound because these actions may rupture the DM. Just as the demarcation furrow reaches the trephination wound margins, the injection of viscoelastic material is stopped and the needle is withdrawn. The stab knife is used to incise the roof of the bubble (Figure 10).

The stromal tissues at the anterior wall of the bubble are excised using curved blunt-tipped corneal scissors (18010; Moria, Antony, France) around the trephination wound circumference (Figure 11).

The DM is exposed to the full extent (Figure 12).

The donor tissue is prepared by disinserting the DM and endothelium from peripheral insertion using a dry Weck-Cel® sponge and wiping it off from the posterior surface of the corneal stroma. A vital dye can be used to stain the endothelium and DM for discriminating the layer from stromal tissues and easy removal of the layer, but I usually put the donor tissue over the back surface of a steel container. The shining reflex of the steel surface facilitates the visualization of the delicate DM (Figure 13).

When no big bubble is formed, the procedure is continued by hydrating a localized area in the stroma with BSS. There is no need for introducing a needle into the corneal stromal tissues for hydrating the collagen fibers; instead we can use a blunt-tipped cannula attached to a syringe filled with BSS to hydrate the stromal tissues by putting the blunt tip in close contact with the stromal tissues in a perpendicular direction and injecting fluid while depressing the tissues by the tip of the cannula (Figure 7). Air injection is repeated in the hydrated area using the same 27-gauge needle and an air-filled syringe. After the sunnyside up sign is seen, the 27-gauge needle used for air injection is attached to a syringe containing viscoelastic material (Coatel™; Bausch & Lomb, Madison, NJ). Viscoelastic material is injected while the needle is inserted into the bubble cavity in the horizontal

The injection of the viscoelastic material into the bubble cavity is continued slowly as the

Care must be taken not to depress the cornea while injecting the viscoelastic material or to overexpand the bubble beyond the trephination wound because these actions may rupture the DM. Just as the demarcation furrow reaches the trephination wound margins, the injection of viscoelastic material is stopped and the needle is withdrawn. The stab knife is

The stromal tissues at the anterior wall of the bubble are excised using curved blunt-tipped corneal scissors (18010; Moria, Antony, France) around the trephination wound

The donor tissue is prepared by disinserting the DM and endothelium from peripheral insertion using a dry Weck-Cel® sponge and wiping it off from the posterior surface of the corneal stroma. A vital dye can be used to stain the endothelium and DM for discriminating the layer from stromal tissues and easy removal of the layer, but I usually put the donor tissue over the back surface of a steel container. The shining reflex of the steel surface

direction with a rapid movement.

"egg yolk" is expanded slowly (Figures 8-9).

Fig. 9. Viscoelastic material is injected into the bubble cavity.

used to incise the roof of the bubble (Figure 10).

The DM is exposed to the full extent (Figure 12).

facilitates the visualization of the delicate DM (Figure 13).

circumference (Figure 11).

Fig. 10. Anterior wall of the bubble is incised using a stab knife.

Fig. 11. Anterior wall of the bubble is excised using blunt tip curved scissors along the trephination wound circumference leaving no corneal stromal tissues within the trephination wound area.

Manual Deep Anterior Lamellar Keratoplasty 67

After this stage no manipulation of the recipient's bed is allowed because no endothelium is present in the donor tissue for converting to penetrating keratoplasty if required. I always remove any residual episcleral and scleral tissues except a small rim around the limbus because those excessive tissues may cause decentered punching of the donor tissue if the

Conversely, care must be taken not to violate the limbus. Cutting the limbal tissues by scissors will result in an ellipsoid rather than round donor button. Loose corneal epithelium may result in donor tissue slippage and decentered punching if the donor tissue is not fresh.

Fig. 15. Geometrical center of the donor cornea is considered as the center for cutting the

punch is not equipped with a suction system (Figure 14).

Fig. 14. Execcive scleral tissues are excised.

donor tissue using a corneal punch.

Fig. 12. Descemet mambrane is exposed troughout the entire trephination wound area.

Fig. 13. Dry Weck-Cel sponge is used for disinserting DM from the peripheral insertions and wipping it off from posterior surface of the donor cornea.

Fig. 12. Descemet mambrane is exposed troughout the entire trephination wound area.

Fig. 13. Dry Weck-Cel sponge is used for disinserting DM from the peripheral insertions

and wipping it off from posterior surface of the donor cornea.

After this stage no manipulation of the recipient's bed is allowed because no endothelium is present in the donor tissue for converting to penetrating keratoplasty if required. I always remove any residual episcleral and scleral tissues except a small rim around the limbus because those excessive tissues may cause decentered punching of the donor tissue if the punch is not equipped with a suction system (Figure 14).

Fig. 14. Execcive scleral tissues are excised.

Conversely, care must be taken not to violate the limbus. Cutting the limbal tissues by scissors will result in an ellipsoid rather than round donor button. Loose corneal epithelium may result in donor tissue slippage and decentered punching if the donor tissue is not fresh.

Fig. 15. Geometrical center of the donor cornea is considered as the center for cutting the donor tissue using a corneal punch.

Manual Deep Anterior Lamellar Keratoplasty 69

Fig. 17. The exposed surface of the DM is irrigated with free-flowing solution.

Fig. 18. Cardinal sutures are placed

Hence, if the corneal epithelium is loose and edematous it must be wiped away using an applicator. The precise geometric center of the donor cornea is determined and marked. The donor cornea devoid of endothelium is put in a corneal punch (Katena Products) using the mark for centration (Figure 15) and is cut to the desired size.

I routinely put some viscoelastic material over the punch blade before cutting, which is useful in creating a more even and smoother edge of the cut donor button. Conversely, the edge of the donor button might become "s" shaped especially if the punch blade is not sharp enough (Figure 16).

Fig. 16. A coin shape donor button with vertical edges is achieved.

Ultimately, the donor button is secured in the recipient site with sutures (10-0 nylon). The exposed surface of the DM is irrigated with free-flowing BSS for removing the viscoelastic material completely after placing the first corneal suture (Figure 17). I prefer to perform mixed continuous and separate sutures (Figures 18-20). In the TALK procedure the depth of the sutures traveling through the corneal tissues is identical at both sides of the graft interface and is approximately 80% to 90% of the corneal thickness at both donor and host tissue sides. If no big bubble is formed after several attempts at air injection, a deep lamellar dissection is performed with a crescent knife to the pre-Descemet level. The tiny air bubbles can be recognized at the DM—stroma interface under high microscopic magnification. The viscoelastic material is injected after inserting the tip of a 30-gauge needle attached to the viscoelastic syringe into a tiny bubble and the bubble will begin to expand. If the overlying collagen fibers are not removed sufficiently, the bubble will expand into the anterior chamber and the surgeon must drain the aqueous fluid from the anterior chamber to provide space for the bubble to expand. If the overlying collagen fibers are minimal, the bubble will expand over the DM toward the outer space and the procedure will continue as described above.

Hence, if the corneal epithelium is loose and edematous it must be wiped away using an applicator. The precise geometric center of the donor cornea is determined and marked. The donor cornea devoid of endothelium is put in a corneal punch (Katena Products) using the

I routinely put some viscoelastic material over the punch blade before cutting, which is useful in creating a more even and smoother edge of the cut donor button. Conversely, the edge of the donor button might become "s" shaped especially if the punch blade is not sharp

mark for centration (Figure 15) and is cut to the desired size.

Fig. 16. A coin shape donor button with vertical edges is achieved.

Ultimately, the donor button is secured in the recipient site with sutures (10-0 nylon). The exposed surface of the DM is irrigated with free-flowing BSS for removing the viscoelastic material completely after placing the first corneal suture (Figure 17). I prefer to perform mixed continuous and separate sutures (Figures 18-20). In the TALK procedure the depth of the sutures traveling through the corneal tissues is identical at both sides of the graft interface and is approximately 80% to 90% of the corneal thickness at both donor and host tissue sides. If no big bubble is formed after several attempts at air injection, a deep lamellar dissection is performed with a crescent knife to the pre-Descemet level. The tiny air bubbles can be recognized at the DM—stroma interface under high microscopic magnification. The viscoelastic material is injected after inserting the tip of a 30-gauge needle attached to the viscoelastic syringe into a tiny bubble and the bubble will begin to expand. If the overlying collagen fibers are not removed sufficiently, the bubble will expand into the anterior chamber and the surgeon must drain the aqueous fluid from the anterior chamber to provide space for the bubble to expand. If the overlying collagen fibers are minimal, the bubble will expand over the DM toward the outer space and the procedure will continue as

enough (Figure 16).

described above.

Fig. 17. The exposed surface of the DM is irrigated with free-flowing solution.

Fig. 18. Cardinal sutures are placed

Manual Deep Anterior Lamellar Keratoplasty 71

The eye is examined on the first postoperative day and after a week. In these visits special attention is focused on the corneal epithelium. Usually a bandage soft lens and nonpreserved lubricant drops are used to improve reepithelialization of the cornea. Topical steroids and antibiotics are started on the first postoperative day. Topical antibiotics are discontinued after the epithelium heals completely. Topical steroids are tapered off over a 4 month period. The patient visits at monthly intervals for 4 months. During this period, every loose suture must be removed and replaced by a new suture. Adjustment of the tension of the continuous sutures can be performed during this period. After the fourth month the patient is examined every 2 months. At the 6-month postoperative visit and beyond the corneal sutures are selectively removed to improve visual function. I routinely remove sutures with the guide of retinoscopy alone and rarely a topographic corneal image is needed to determine the suture that requires removal. I remove the continuous suture if the spherical equivalent is over +3 and remove radial sutures along the steepest corneal meridian (the most "with movement" of the light reflex intercept while performing

Perforation of the DM can occur during trephination. In this instance the wound must be sutured and the operation is better postponed to a time after the wound has healed for

Perforation can also occur after penetration by the tip of the needle for air injection, in which case air immediately enters the anterior chamber. No attempt to expose the bare DM should

When the large-bubble or expanding-bubble technique is used, perforation of the DM may occur after the DM—stroma interface is overfilled. A horizontal radial tear appears at the center of the DM along the 3-to-9 o'clock meridian. It is wise to convert these surgeries to penetrating keratoplasty because trying to oppose the DM to the posterior surface of the donor cornea using gas tamponade is difficult. Even if this procedure is successfully performed, it is associated with opacification and scar formation over an elliptical area (fishmouth shape) in the posterior corneal surface that is devoid of DM. The opacification has

Perforation of the DM can occur during lamellar dissection and tissue removal. In these cases a pre-Descemet DALK can be performed. The perforation site must be left until the end of tissue removal and a small amount of stromal tissue must be left over the perforation

If an instrument touches the bare DM, perforation is possible. In most of these cases the procedure can be continued by thoroughly washing any retained viscoelastic material, suturing the donor tissue in place, and using air for intracameral injection to seal the perforation. Because the dome-shaped contour of the cornea is reduced, especially with tight sutures, the air bubble in the anterior chamber will apply noticeable pressure over the pupil to induce papillary block. Performing a peripheral iridotomy via a paracentesis is necessary and infusion of a hyperosmotic solution such as 20% mannitol is necessary to induce vitreous shrinkage if not contraindicated according to the patient's general status.

be made. However, a pre-Descemet DALK could be performed in these cases.

**5. Follow-up schedule** 

retinoscopy).

**6. Complications**

**6.1 Perforation of the DM** 

site to seal the perforation.

planned pre-Descemet level DALK.

adverse visual effects because it is centrally located.

Fig. 19. Eight separate radial sutures are tied and Burried in the donor button.

Fig. 20. Suturing the donor button in the recipient bed is completed using combined Interrupted and continuous sutures.
