Femtosecond laser-enabled keratoplasty offers wound shape flexibility

Roger F. Steinert, MD, describes the technique and tells surgeons to closely follow the steps from the training videos in their early cases.

Introduction

Thomas John

Corneal transplantation continues to move in new directions in the arena of full-thickness penetrating keratoplasty and partial-thickness lamellar keratoplasty.

Lamellar keratoplasty or selective tissue corneal transplantation involves only the diseased portion of the recipient cornea being replaced with similar healthy tissue, whereas in PK, the entire recipient cornea within the circular trephination area is replaced with full-thickness donor corneal tissue.

A manual PK wound is usually vertical, and variations from this type of wound construction are not easily possible in the manual PK techniques. Variations from a vertical wound in PK include top hat, mushroom, zigzag, Christmas tree, zigsquare and other configurations (Figure 1).

Some of these wound shapes were initially described by José Ignácio Barraquer in 1950. Recently, there has been a newfound interest in these new wound shapes. These newer wound constructions in PK have been associated with better wound integrity, presumed faster donor-recipient junction wound healing, earlier suture removal, less surgically induced corneal astigmatism and earlier visual rehabilitation.

Figure 1. Schematic representation of a zigzag femtosecond laser-enabled keratoplasty (FLEK) (top center); various schematic shapes of FLEK procedure from top hat to zig square (bottom row). Images: Steinert RF

The femtosecond laser has enabled these newer shapes of wound construction for femtosecond laser-enabled keratoplasty (FLEK). In this issue, Dr. Roger Steinert discusses his technique of performing FLEK.

by Thomas John, MD
OSN Corneal Dissection Editor

Anesthesia

Roger F. Steinert

Preferred anesthesia is retrobulbar or general anesthesia. Do not use topical anesthesia for this surgical procedure.

Step-by-step surgery

The laser settings on the donor and recipient corneas are identical, with one exception. The donor cornea is cut full-thickness, with the laser depth set deeper than the peripheral corneal thickness.

Donor cornea

A standard setting of 850 µm guarantees that the laser will begin in the artificial anterior chamber. This can be verified by the appearance of bubbles in the artificial anterior chamber. Because the zigzag anterior incision is beveled, we have not found any need to change our settings if the donor has epithelium or is de-epithelialized.

The settings for zigzag pattern FLEK are:

• Lamellar ring-cut depth of 300 µm;
• Tangential and radial spot separation of 4 µm;
• Anterior side-cut posterior depth of 330 µm and an angle of 30°;
• Posterior side-cut anterior depth of 270 µm and a side-cut angle of 30°;
• Alignment incisions in donor consisting of 16 incisions, with posterior depth 100 µm, length 1,250 µm, width 50 µm, radial offset –2, spot separations all set at four;
• Alignment incisions in the patient consisting of eight radial incisions (Figure 2) — same parameters as in donor — except a radial offset between +1 and +2; as much as the corneal diameter will permit.

The remaining variable is diameter. For keratoconus, most patients have enough corneal diameter for a 9 mm outer diameter. Other standard diameters are 8.5 mm and 8 mm. Because the laser settings are identical for the donor and recipient corneas, with one exception (see above), when these smaller diameters are chosen, subtract the reduced amount from the default values given below:

• Ring outer diameter 9.1 mm and inner diameter 7.9 mm;
• Anterior side-cut anterior diameter 9 mm;
• Posterior side-cut diameter 9.1 mm.

Recipient cornea

When the laser incision is performed outside of the operating room, usually in a laser center, a bridge of about 70 µm of uncut posterior stroma is necessary for safety.

To accomplish this, we measure the peripheral thickness of the patient’s cornea, take the lowest value and subtract 70 µm. The easiest way to get the pachymetry reading is with anterior segment optical coherence tomography, but an ultrasonic pachymeter is also acceptable.

The alignment incisions in the patient’s cornea consist of eight radial incisions (Figure 2) — same parameters as in donor (see above) — except a radial offset between +1 and +2; as much as the corneal diameter will permit. The other laser settings for the patient’s cornea, including the diameter of the laser incisions, are described in the previous section.

Figure 2. The completed laser incision on the patient’s cornea is seen (top row left); The eight laser-induced alignment incisions in the patient’s peripheral cornea is highlighted with a surgical marking pen (top row right); Intraoperative photographs displaying the gentle dissection of the corneal tissue bridges within the laser incision using a Sinskey hook (bottom row).

Figure 3. Completion of the gentle dissection of the corneal tissue bridges is seen within the laser incision (top row); Anterior chamber is entered with a super blade (bottom row left); The recipient corneal cut is completed with corneal microscissors, keeping the blade and the scissors at an angle that respects the 30° laser bevel (bottom row right).

Immediately after the laser incision on the recipient cornea that is performed in the laser center, we instill antibiotic drops, namely Iquix (levofloxacin 1.5%, Vistakon), Vigamox (moxifloxacin 0.5%, Alcon) or Zymar (gatifloxacin 0.3%, Allergan), and apply a gentle pressure patch.

In the operating room, the tissue bridges are dissected gently with a Sinskey hook (Figures 2 and 3). After the posterior side cut is opened 360°, the anterior chamber is entered with a 15° super blade (Figure 3), and the cut is completed with corneal microscissors, keeping the blade and the scissors at an angle that respects the 30° laser bevel (Figure 3).

Figure 4. The central full-thickness corneal disc is removed using 0.12 forceps, exposing the patient’s anterior iris surface (top row); The donor corneal disc prepared using the laser incision is sutured to the patient’s cornea initially with four-cardinal, interrupted 10-0 nylon sutures (bottom row).

Figure 5. After the cardinal sutures, the 24-bite, running 10-0 nylon suture is placed (top row left); The cardinals are removed after all 24 bites of the 10-0 nylon suture are completed. The knot is buried within the host corneal incision (top row right); The corneal shape is checked, and the suture tension is redistributed to obtain the optimal shape with minimal intraoperative astigmatism (bottom row left); The completed view of the FLEK procedure (bottom row right).

For suturing the donor cornea to the recipient, I prefer a 24-bite running suture, unless there is vascularization or inflammation that would warrant a combined running and interrupted or pure interrupted sutures. I use a 10-0 nylon suture in all cases. My technique for the running suture is to first place four cardinal sutures (Figure 4).

Accurate distribution of the tissue is assured by the radial marks (Figure 4). These are easily seen on the donor cornea. On the host, they are difficult to see if the epithelium becomes hydrated, so before dissecting and removing the patient’s cornea, mark the radial marks with a fine point gentian violet pen (Figure 2).

After the cardinal sutures are placed, the running suture is placed (Figure 5). The consistency of the length of the suture in the donor cornea is greatly enhanced by the radial marks, which is why they are set at the above parameters.

There are 16 marks on the donor cornea. For a 24-bite running suture, each pass occupies one-third of the space. I place one pass directly through a mark, then move one-third of the distance to the next mark, then another one-third, then the subsequent pass will be directly on a mark again (Figure 5).

In this manner, each quadrant has six suture passes. The cardinals are removed after all 24 bites are completed. The knot is buried within the host corneal incision. Figure 6 shows the clinical biomicroscopic and OCT views of a FLEK procedure.

Figure 6. Displays of the clinical biomicroscopic (left) and OCT (right) views of a FLEK procedure.

Surgical pearls and tips

• IntraLase (Abbott Medical Optics) provides some standard laser settings, and the SightLife and Tissue Banks International eye banks use standard settings to facilitate ordering precut donor corneal tissue. If you wish a custom pattern, this can be specified, but make sure that your parameters result in a valid intersecting cut pattern.
• Do not improvise in your early cases. IntraLase has training videos on each of the steps. Follow them closely.

Postoperative treatment

During the immediate postoperative period, medications include topical antibiotics four times a day, such as levofloxacin 1.5%, moxifloxacin 0.5% or gatifloxacin 0.3%, and a topical steroid four times a day, namely Durezol (difluprednate ophthalmic emulsion 0.05%, Sirion Therapeutics) or Pred Forte 1% (prednisolone acetate 1%, Allergan).

References:

• Bahar I, Kaiserman I, Lange AP. Femtosecond laser versus manual dissection for top hat penetrating keratoplasty. Br J Ophthalmol. 2009; 93(1):73-78.
• Barraquer, JI. Keratoplasty: Problems arising from the fixation of the graft. Britannia Acta. 1951;2:999–1004.
• Farid M, Kim M, Steinert RF. Results of penetrating keratoplasty performed with a femtosecond laser zigzag incision initial report. Ophthalmology. 2007;114(12):2208-2212.
• John T. Lamellar Corneal Surgery. New York, USA: The McGraw-Hill Companies; 2008.
• John T. Selective tissue corneal transplantation: a great step forward in global visual restoration. Expert Rev Ophthalmol. 2006;1:5-7.
• John T. Step by Step Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
• John T. Surgical Techniques in Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
• Malta JB, Soong HK, Shtein R, et al. Femtosecond laser-assisted keratoplasty: Laboratory studies in eye bank eyes. Curr Eye Res. 2009; 34(1):18-25.
• Steinert RF, Ignacio TS, Sarayba MA. “Top hat”-shaped penetrating keratoplasty using the femtosecond laser. Am J Ophthalmol. 2007;143(4):689-691.

• Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com. Dr. John is a speaker for Vistakon Pharmaceuticals.
• Roger F. Steinert, MD, can be reached at the Gavin Herbert Eye Institute at University of California, Irvine, 118 Med Surge I, Irvine, CA 92697-4375; 949-824-8089; e-mail: steinert@uci.edu. Dr. Steinert is a consultant for Abbott Medical Optics.