Automated lamellar therapeutic keratectomy (ALTK) is a promising treatment option for cases of lost caps and patients with recalcitrant striae or scarring after LASIK. This relatively new procedure poses less risk to patients than a full corneal transplant.
WHY ALTK?Free Caps
In patients who have lost a portion of their cornea, the cut edge of their stroma is not as smooth as it would be after laser ablation. When I see these individuals, their eyes have usually been left to re-epithelialize.
I prefer ALTK to a full penetrating keratoplasty in these patients for three reasons: (1) ALTK produces far less irregular astigmatism; (2) rejection is much less of a problem with ALTK; and (3) ALTK patients require medication for a shorter duration.
Striae and Scarring
When a patient's striae persist after ironing or stretching procedures, and scarring has opacified the edge of the fold of the flap, I have resorted to ALTK. Amputating the flap would leave these individuals' stroma as the front surface of their eyes until they re-epithelialize, so their visual acuity is typically poor. ALTK gives patients the benefit of Bowman's membrane, which is smoother than the stroma, so they have superior visual acuity.
Preparing the Treatment Site
After sedating and positioning the patient under the microscope, I clean up the area that I will be treating. In particular, I remove the epithelium and any scarring, which can be substantial in patients who lost their cap long before seeing me (6 months was the latest).
Scarring is usually subepithelial. I will use a 0.12 forceps to separate out the scar tissue, which peels off as a sheet or linearly, depending on its shape (Figure 1). I then apply 0.02% mitomycin C to the bed with a trephinated sponge for 2 minutes.
Measurements
Next, I measure the horizontal and vertical diameters of the treatment site (Figure 2), and I assess the peripheral portion of the bed where it bevels with the patient's normal tissue. I always request donor tissue with at least 3 mm of scleral rim, because I want to be able to hold the corneoscleral area watertight in the ALTK system artificial chamber (Moria Inc., Doylestown, PA).
I use BSS (Alcon Laboratories, Inc., Fort Worth, TX) on a gravity feed, so I place the bottle as high as possible in the OR in order to raise the IOP, which I then measure with applanation tonometry. The target pressure is above 65 mm Hg. The Moria system's fine-pitched rotating dial allows me to raise and lower slightly the stage where the microkeratome will be set in order to adjust the diameter of the donor tissue. I do so by placing applanating lenses with circles of specific diameters on the stage and adjusting the height until the applanated area matches the desired circle size. (Figure 3)
When replacing a lost cap, I want the diameter of the donor tissue to be slightly smaller than the host area. The reason is that, when the stromal portion of the donor tissue overlaps the epithelial portion of the host area, epithelial ingrowth becomes more likely. I have found that leaving a gutter around the donor button lessens this problem.
If the donor button I have created is too large for the host area, I cut it down with a trephine. This is not an ideal solution, because the trephinated edge of the donor tissue will be perpendicular while the host area has a beveled edge. Spending the time to properly align the correctly sized applanating lens with the applanated area of the cornea before cutting the donor tissue has helped me to obtain correctly sized donor buttons.
Harvesting and Placing the Cap
I use the LSK One microkeratome with the 130 or 150 heads (Moria Inc.), which cut caps approximately 160 µm or 180 µm thick, respectively. A straight pass of the microkeratome head across the entire cornea produces the cap, which I then harvest (Figure 4).
I sew the cap into place on the eye, usually with approximately eight bites of an interrupted or running antitorque suture through the donor tissue (Figure 5). The sutures may be loose because their purpose is not to hold the cap watertight. Some surgeons use a mattress suture over the donor tissue, but I have found that this technique can lead to epithelial ingrowth if the edges of the tissue are insecure.
THE PROCEDURE FOR FLAPS WITH STRIAE
These patients typically have some sort of anterior flap on their eyes. Removing the entire flap would make replacing it challenging, because amputation will produce a D-shaped host area that will be difficult to match when cutting the donor material.
After measuring the size of the flap, I will use a vacuum trephine such as the Hanna trephine system (Moria Inc.) to create the host area. The vacuum helps me secure the trephine onto the cornea in order to maintain a stable position, and the Hanna trephine system allows a measured depth to the cut. If I have information on the flap thickness from the original surgery,
I will make my cut 25 µm deeper. If no reliable information on the original flap is available, I will trephine to a depth of 200 µm. I am usually able to create a host area of 7.5 to 8.0 mm in diameter without a problem, because the flaps tend to be sized slightly larger than that. It is important, however, to create a host area slightly smaller than the periphery of the flap. A rim of flap tissue sized 0.75 mm at minimum will allow adequate room for suturing; if the original flap is smaller than 9 mm, the trephine size will therefore need to be 1.5 mm smaller in diameter in order to hold everything in terms of sizing.
Using the ALTK system artificial chamber, I will harvest a large, lamellar donor cap in the same manner as for cap replacement; I aim for the largest possible diameter. I then use a trephine to cut a donor cap of the same diameter as I have trephined from the recipient bed. I peel back the trephinated central portion of the original flap and place the donor button. Next, I loosely suture the cap into place with an eight-bite interrupted or antitorque suture. I leave the sutures in place and remove them in 1 to 2 months.
PATIENT HISTORY
If possible, I ascertain which microkeratome was used on the patient during the original LASIK procedure and the average flap thickness the surgeon has obtained with that instrument. This information gives me an idea of the host tissue I am trying to replace. I use ultrahigh-frequency ultrasound to determine the thickness of the flap in patients with recalcitrant striae. If I have no information in terms of flap thickness, I will use donor tissue that is 180 to 200 µm thick. This choice has not resulted in problems for me so far.
POSTOPERATIVE MANAGEMENT
I place patients on Pred Forte (Allergan, Inc., Irvine, CA) q.i.d. for 1 month and then slowly taper the dosage. There have been reports of epithelial cell rejection and haziness in the flaps due to stopping steroid treatment too quickly.1
CONCLUSION
The patients on whom I have performed ALTK have been concerned about their visual acuity and ocular health. Usually, they have already undergone a procedure in the OR for a complication from their elective refractive surgery. As part of the informed consent, it is important to discuss the relative novelty of the procedure with patients.
Surgeons who are comfortable with microkeratome technology are the most likely to excel with ALTK. I have performed the procedure on eight patients without incident, and I have been pleased by the improvement in their BSCVA from a median of 20/100 (range 20/50 to 20/400) to between 20/20 and 20/30 (median 20/25) postoperatively.
Barrie D. Soloway, MD, is Director of Vision Correction Surgery and Assistant Professor of Ophthalmology at the New York Eye and Ear Infirmary in New York. He holds no financial interest in the products mentioned herein. Dr. Soloway may be reached at (212) 758-3838; bsolowaymd@pol.net.1. Culbertson W. Anterior and posterior lamellar keratoplasties. Paper presented at: Moria Breakfast Scientific Session; June 3, 2002; Philadelphia, PA.
