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Up Front | Jan 2008

Half-Depth Corneal Scar After PRK

A laser malfunction left a linear scar extending into the optical zone.

In June 2005, a 24-year-old woman underwent PRK in both eyes for correction of an initial myopia of -4.50 D. The excimer laser the surgeon used was part of a mobile unit that was carried on a truck and moved from one refractive center to another.

Treatment of the right eye was uneventful. During treatment of the left eye, however, a malfunction of the mirrors inside the laser system resulted in the application of laser spots concentrated along one horizontal line in the prepupillary area (Figure 1). The resulting scar extended halfway into the stroma (Figure 2) and caused a notable loss in BCVA (0.4 with a refraction of -1.75 -2.25 X 100º in December 2007), blurriness, and double vision. Corneal topography revealed a reversed central island (Figure 3). The central corneal pachymetry was 467 µm.

What would you suggest to improve the situation in this patient's left eye?

Case presented by Jérôme C. Vryghem, MD.

This case presents the typical indication for a superficial automated lamellar keratoplasty (SALK). In SALK, a dedicated microkeratome with a 130-µm head (Moria, Antony, France) is used to create a free cap that includes the superficial scar. If the cornea is thick enough, as in this specific case, a 200-µm head can be used to perform a deeper keratectomy and entirely eliminate even a scar reaching more deeply.

A donor lamella is obtained using the same microkeratome, always mounting the 130-µm head, regardless of the amount of tissue removed from the host. This type of thin graft can simply be laid on the recipient bed, and either a therapeutic contact lens or overlay sutures can be used to secure it into position. To fixate thicker grafts, conventional radial sutures are required; they must be kept in place for months. This considerably slows down visual recovery.

Overlay sutures can be removed within 1 week after surgery, and the corneal shape stabilizes in 4 to 6 weeks.

In the presence of sufficient thickness in the host cornea, residual refractive error can be managed by simply lifting the free cap graft (as early as 2 to 3 months after SALK) and performing laser ablation on the recipient bed surface. In this way, an unsuccessful PRK can be converted into successful LASIK (Figures 4A and B).

SALK is an effective, simple, and standardized technique. It removes diseased corneal tissue independent of its structural or optical homogeneity, thus offering a significant advantage over phototherapeutic keratectomy, which has been reported to produce mixed results in cases such as the one presented herein. Finally, unlike with conventional penetrating keratoplasty, visual rehabilitation is rapid, and stabilization of the corneal architecture can occur in just a few weeks.

Before deciding on a therapeutic approach, I would first want to have two additional diagnostic assessments, a Visante OCT (Carl Zeiss Meditec AG, Jena, Germany) or confocal microscopy study to properly evaluate the depth of the scar, and visual and refractive evaluation with a rigid contact lens (RCL). With this information, we may imagine several scenarios:

  • BCVA with an RCL is 20/25 or better. (Irregular astigmatism is the main problem.) In this case, I would definitely attempt a topography-guided treatment (transepithelial PRK) with the MEL 80 excimer laser (Carl Zeiss Meditec AG). The prescription of an RCL could also be an option in this case, if acceptable to the patient.
  • BCVA with the RCL is 20/40 or worse. (Opacity is the main problem.) In this case, I would recommend deep anterior lamellar keratoplasty. My preferred option would be a pre-Descemet's membrane manual dissection. If a femtosecond laser lamellar cut is used, we must be certain to design a cut that goes below the scar. Several months after lamellar surgery, we should be able to correct residual refractive error either with corneal or intraocular (phakic IOL) refractive surgery or a combination of both.
  • BCVA with the RCL is between 20/40 and 20/25. The choice of approach will depend on the patient's subjective complaints/needs, eye dominance, and the patient's final realistic expectations.

Since the surgery was performed more than 2 years ago, the linear scar appears to have had enough time to fade or undergo epithelial recontouring, which might have minimized the distortion. Therefore, the visual result will be permanent if not corrected. If the scar is half-thickness, then a phototherapeutic keratectomy would not be helpful, because the cornea would be left too thin.

As there appears to still be a significant amount of surface irregularity, a microkeratome dissection may not provide sufficient improvement in the visual result. I would recommend either a deep anterior dissection or big-bubble technique with full-thickness donor grafting to correct the scarring. The patient should be advised that she will most likely still need laser refractive surgery at a later date to correct residual myopia and astigmatism.†

I have encountered several similarly irregular corneas secondary to infection, irregular ablation, and/or trauma. Keeping penetrating keratoplasty in mind as the definitive final treatment if everything else fails, I would employ our experience over the past 6 years with topography-guided ablation and collagen cross-linking.

Topography-guided surface ablation can be used to smooth the irregularity. I would treat 75% of manifest sphere and cylinder. The WaveLight AG (Erlangen, Germany) excimer laser platform has the longest and most successful results with this treatment modality.

In conjunction with this treatment, at the same sitting, I would perform collagen cross-linking on this cornea for several reasons: (1) to reduce corneal scarring (cross-linking eliminates keratocytes for about 6 months to a depth of 300 µm), (2) to reduce the chance of scarring from the PRK, and (3) to stabilize the potentially thinner cornea postoperatively.

Figures 5 and 6 illustrate our experience with this treatment combination in a case similar to the one presented here. The patient's eye had contact lens–related corneal scarring and vascularization with BCVA of 20/100 (Figure 5). Pentacam-guided (Oculus Optikger‰te, Wetzlar, Germany) PRK and collagen cross-linking (0.1% riboflavin plus 7 mW/cm² UV light exposure for 15 minutes) were performed (Figure 6). The postoperative result can be seen in Figure 3.

In a case such as this, I would be pleased with a result of 20/40 or better, which compares favorably with the average corneal graft results. The procedure can be further complemented with a second PRK in the future, if needed.

Massimo Busin, MD, is a Professor of Ophthalmology and Director of Ophthalmology at Villa Serena Hospital, Forli, Italy. He may be reached at mbusin@yahoo.com.

José L. Güell, MD, is Director of the Cornea and Refractive Surgery Unit at the Instituto de Microciruglía, in Barcelona, Spain, and an Associate Professor of Ophthalmology at the Autonoma University of Barcelona. Dr. Güell states that he is a consultant to Carl Zeiss Meditec AG. He may be reached at +34 93 253 15 00; guell@imo.es.

Francis W. Price Jr, MD, is in private practice at Price Vision Group, Indianapolis, Indiana. He states that he has no financial interest in the products or companies mentioned. Dr. Price may be reached at +1 317 814- 2823; fprice@pricevisiongroup.net.

A. John Kanellopoulos, MD, is Director of Laservision Eye Institute, in Athens, Greece. He is an Attending Surgeon for the Department of Ophthalmology at the Manhattan Eye, Ear, & Throat Hospital, in New York and a Clinical Associate Professor of Ophthalmology at New York University Medical School. Dr. Kanellopoulos states that he has no financial interest in the products or companies mentioned. He is a member of the CRST Europe Editorial Board. Dr. Kanellopoulos may be reached at +30 21 07 27 27 77; laservision@internet.gr.

Jérôme C. Vryghem, MD, is from the Brussels Eye Doctors, in Brussels, Belgium. Dr. Vryghem states that he has no financial interest in the products or companies mentioned. He is a member of the CRST Europe Editorial Board. He may be reached at +32 2 741 69 99; j.c.vryghem@vryghem.be; info@vryghem.be.