Penetrating keratoplasty (PKP) is the most frequently used and reliable surgical technique available to treat keratoconus. However, the procedure compromises the corneal endothelium, which is usually still healthy in eyes with this disease, and puts patients at risk for immunologic rejection.¹ PKP causes an annual endothelial cell loss of 7.8% between 3 and 5 years after surgery.² Because keratoconic patients are usually young, we must follow a step-by-step therapeutic plan, choosing, when possible, less-invasive techniques that postpone PKP.

Different techniques for anterior lamellar keratoplasty have been proposed as an alternative to PKP. Common principles for these techniques include selective removal of only pathologic tissue, preserving the deeper corneal layers (ie, Descemet's membrane and endothelium), and restoration of normal corneal thickness with a lamellar graft. The use of lamellar stromal grafts avoids the unnecessary transplantation of healthy endothelium.³ In fact, any form of lamellar keratoplasty has two advantages over PKP: (1) the procedure is extraocular, and intraoperative complications (eg, endophthalmitis and expulsive hemorrhage) are therefore minimized, and (2) steroid therapy can be discontinued much earlier than after PKP, reducing the risk for posterior capsular opacification and glaucoma.

However, hand dissection is a difficult, painstaking procedure that is rarely as precise as required. Hand-dissected donor and recipient corneas often have postoperative scar tissue formation, increased light scattering, and, thus, limited vision. If hand dissection is performed deep in the recipient cornea, visual results may improve;⁴ however, the accuracy of stromal removal is strongly dependent on the surgeon's skills, with low reproducibility. Moreover, the learning curve is demanding, and intraoperative complications that often require conversion to PKP are frequent, even in experienced hands.³ As a result, most keratoplasty surgeons have been unwilling to abandon a well-established technique, such as PKP, in favor of a time-consuming method with an unknown long-term outcome, such as lamellar keratoplasty.

Some surgeons have recently begun using the excimer laser to remove the recipient corneal stroma, leaving a quality stromal bed surface.⁵ Excimer laser lamellar keratoplasty (ELLK) of augmented thickness was conceived as an alternative to PKP for the treatment of keratoconus. To simplify and standardize lamellar keratoplasty, ELLK is used to prepare the recipient bed. Results in a small series are encouraging.⁶ In our experience,⁷ excimer laser-assisted dissection is a reproducible technique that requires a short surgical time.

We conducted a study of 41 patients with keratoconus and poor vision despite spectacle or contact lens correction, poor contact lens tolerance, superficial corneal opacity, and pachymetry greater than 350 µm. Patients with diabetes, connective tissue disorders, glaucoma or intraocular hypertension (greater than 20 mm Hg), dry-eye, retinal disorders, or amblyopia were excluded. All patients had a complete eye examination, including UCVA and BCVA, refraction, slit-lamp biomicroscopy, intraocular pressure measurement, and fundus evaluation. Corneal topography was performed during each examination, and corneal thickness was evaluated using a 50-MHz ultrasound pachymeter. The corneal endothelial pattern was evaluated using noncontact endothelial specular microscopy. Measurements were taken preoperatively and 3, 6, 12, and 24 months postoperatively.

SURGICAL TECHNIQUE
Local anesthesia (10 cc bupivacaine 0.5%/mepivacaine 4.0%) was given by peribulbar injection. After mechanical deepithelialization, phototherapeutic keratectomy was performed with the MEL 70 excimer laser (Carl Zeiss Meditec, Jena, Germany) using the following settings: wavelength, 193 nm; frequency, 35 Hz; fluence, 180 mJ/cm2; and ablation depth, 0.25 mm. A 7-mm, round, stainless steel mask was placed on the cornea to create a regular vertical ablation edge. The ablation depth ranged from 110 to 200 µm; the goal of the minimum estimated residual corneal bed was set at 200 µm.

A 2.5-mm stromal pocket was created around the circumference of the ablation floor with a circular movement using a disc knife. Donor lamellae were obtained from a cornea mounted on an artificial anterior chamber. Donors were cut with the ALTK System microkeratome (Moria, Antony, France), and then dehydrated in silicone gel. After rehydration in balanced salt solution for 10 minutes, the donor lamella was secured in the recipient bed with four 10-0 nylon cardinal sutures at the 6-, 12-, 9-, and 3-o'clock positions.

The wing of the donor lamella was introduced into the stromal pocket, followed by placement of 16 interrupted 10-0 nylon sutures (Figure 1). Finally, the knots were buried, and intraoperative suture adjustment was performed. At the end of surgery, the speculum was removed and the eye patched.

The patch was removed on the first postoperative day. Therapy consisted of three daily applications of topical ofloxacin 3% until complete reepithelialization. After ofloxacin was discontinued, topical dexamethasone 0.1% was administered for at least 1 month and then tapered and titrated. Within 3 months, all medication was stopped. Preservative-free artificial tears (sodium hyaluronate 0.2%) were used for up to 6 months. Two months after surgery—and based on corneal topography analysis—selected sutures that caused major graft distortion were removed. Over the following 3 months, all remaining sutures were selectively removed to achieve as regular a corneal curvature as possible.

To reduce postoperative refractive error in unsatisfied patients, topography-guided PRK was performed using the MEL 70 excimer laser linked to a computerized videokeratographer (TMS-3; Tomey Corp., Nagoya, Japan) with a topographically supported customized ablation workstation.3 Ablation took place at least 12 months after ELLK and 6 months after complete suture removal.

RESULTS
All patients attended the 3- and 6-month follow-ups. At 1 and 2 years, results were available for 40 and 33 patients, respectively. There were no intraoperative complications. The mean ablation depth was 185.5 ±30.7 µm. The mean diameter of the donor lamellae was 9.0 ±0.3 mm (range, 8.5–9.8 mm), and the mean thickness was 362.7 ±36.3 µm (range, 320–420 µm). All corneas were clear on the first postoperative day, and reepithelialization was complete within 2 weeks after surgery, except in one patient who developed corneal melting and underwent successful PKP 7 months after ELLK. This patient was excluded from the study before the 1-year follow-up. In all other patients, the corneal sutures were removed a mean 3.2 ±2.3 months postoperatively (range, 2–5 months).

All corneas remained clear throughout the study (Figure 2), with no immunologic rejections. There were no cases of corneal vascularization or infection. No compression sutures or limbal relaxing incisions were placed. A mean of 16.6 ±4.7 months after ELLK, seven eyes of seven patients who were unsatisfied with their vision underwent topography-guided PRK to correct a postoperative refractive error. These patients were excluded from the study before the 2-year follow-up.

UCVA and the BCVA were statistically significantly better post- versus preoperatively. The number of patients with a BCVA better than 20/40 after ELLK rose to 37 (92.5%) and 29 (87.9%) at 1 and 2 years, respectively. At 24 months, BCVA had improved by one line in four (12.1%) and by two or more lines in 21 (63.6%) patients. It decreased by one line in three patients (9.0%) and by two or more lines in four (12.1%) patients. In the seven eyes that had topography-guided PRK, UCVA, BCVA, and refraction improved after 6 months.

The mean average keratometry value decreased statistically significantly from pre- to all postoperative visits (P<.0001). At 2 years, corneal topography patterns were classified as regularly astigmatic in 28 (84.8%) eyes. The corneal patterns remained stable in all eyes, with no substantial changes (Figure 3).

The preoperative mean thinnest point on the cornea increased significantly 3 months after ELLK (P=.02). No significant changes in corneal thickness occurred from 3 months to 2 years. There was no statistically significant difference in endothelial cell density or coefficient of variation between pre- and postoperative levels.

DISCUSSION
The contour of the cornea was regular in all cases, despite the wide range of preoperative corneal curvature and degree of surface irregularity.⁸ The advantage of using an excimer laser for lamellar keratoplasty is the laser's ability to remove tissue with microscopic precision. The laser does not interfere with wound-healing processes, including cell migration and proliferation and production of new tissue.⁹ The surgeon sets the depth of laser ablation in relation to the preoperative corneal thickness of the eye, and the laser lamellar keratoplasty can be performed with no risk for dissection errors.

In our procedures, normal thickness (greater than 500 µm) was restored in all eyes by implanting a donor lamella that was thicker than the tissue ablated from the recipient cornea (mean diameter, 9 mm). The peripheral portion of the donor was inserted inside the stromal pocket of the recipient cornea to minimize the risk for interface epithelialization and encourage peripheral scarring between the tissues. After photoablation, the corneal bed maintains an irregular thickness and curvature.

The 360-µm lamella sutured correctly within the peripheral pocket reshapes the anterior surface of the cornea—the most important factor from a refractive viewpoint. Corneal curvature improved by more than 50.00 D because of the flattening effect of the sutures, as described with other lamellar techniques, such as epikeratophakia.

Results of this 2-year study indicate that ELLK may be an alternative treatment for moderate to advanced keratoconus in eyes with a minimum corneal thickness of 350 µm. ELLK provides similar efficacy to PKP, but it is less invasive. It preserves the healthy recipient endothelium, thus producing a higher safety profile.

The use of the excimer laser allowed us to standardize lamellar keratoplasty by simplifying the surgical maneuvers, shortening surgical time, and decreasing intra- and postoperative complications. In the near future, the development of new laser devices and customized ablation algorithms could improve the results and expand treatment indications.

Leopoldo Spadea, MD, is an Associate Clinical Professor of Ophthalmology, Chief of Eye Clinic, S. Salvatore Hospital, University of L'Aquila, L'Aquila, Italy. Professor Spadea states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 0862 319671; e-mail: lspadea@cc.univaq.it.

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