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Up Front | Jan 2006

Surface Irregularity After Enhancement

This is a difficult case because of the highly irregular nature of the patient's cornea, a finding supported clinically by the refraction with high astigmatism and the loss of BSCVA. The wavefront map also shows a great degree of higher-order aberrations, the most notable of which is coma. The Orbscan axial map shows high astigmatism in the center that becomes very irregular toward the periphery around the 3- to 4-mm optical zone area. Of special note is the flattened inferior and temporal area straddling the pupillary border. This location is likely where the sliver of stroma was accidentally removed during the recut.

On this highly irregular cornea, an enhancement with a wavefront-guided excimer laser platform will not work well, because the aberrations may well be out of the range of most wavefront-measuring devices. In simple terms, the cornea may be too irregular to be treated with a wavefront-based procedure. Another consideration is tissue reserve. Wavefront-guided ablations remove tissue according to this rough formula: 3 X (maximal deviation - minimal deviation in microns). It may not be feasible to proceed with wavefront-guided ablation, even if the treatment could be calculated.

My colleagues and I have worked with the Allegretto Wave topography-guided platform (Wavelight Laser Technologie AG, Erlangen, Germany) during the last 3.5 years.1 We presented our data at the American Academy of Ophthalmology 2004 Annual Meeting.2 I would attempt an enhancement with a topography-guided system, because the aberration/irregularity is corneal in origin. It will probably be feasible to obtain reproducible topographies and create a treatment plan.

The topography-guided software from Wavelight that we have used will treat only the relatively steep areas of the cornea — somewhat like a selective phototherapeutic keratectomy (PTK) — in order to generate a smooth central corneal surface. Although we have been pleasantly surprised by such treatments in the past, I should note two caveats from our experience. First, one should not attempt to correct tilt during the topography-guided treatment (an option with the Wavelight platform), because this cornea is so irregular. Second, one should expect a smoothing effect on the cornea but also a possible refractive surprise, because the ablation will be highly irregular to match the irregular nature of this cornea.

My guess is that this eye would experience a myopic shift after such a treatment. I would perform surface ablation in order to avoid any additional flap-related complications. Specifically, I would proceed with a topography-guided PRK using adjunctive 0.2% mitomycin C for 1 to 2 minutes, and I would explain to the patient that a second PRK might be necessary to treat residual spherical error.

I had a similar case. Figure 2 shows the pre- and postoperative topographies of the cornea. This eye had an old, contact lens-related Pseudomonas corneal ulcer that was located slightly temporal to the visual axis. The paracentral cornea was relatively flatter and thinner as a result. In this case, I treated the -3.00 to -3.50 D of irregular cylinder with a topography-guided procedure and believe I achieved a relatively satisfactory result. The difference map shown in Figure 2 depicts the actual laser ablation profile.

ERIK L. MERTENS, MD, FEBO
First, an initial relift of the nasal hinged flap had to be attempted. Even after several years, it is almost always possible to lift the original flap. A recut should be considered as the last possibility. The second flap was more superficial than the initial flap at the temporal edge of the pupillary border, and therefore a small piece of stromal bed tissue between the original flap and the interface needed to be discarded.

This case with irregular corneal astigmatism is challenging. The BSCVA drops to 20/100 with a correction of -2.50 + 3.25 X 55. The Orbscan axial power map (Bausch & Lomb) shows irregular astigmatism. The Customvue wavefront map shows a significant amount of higher order aberrations, especially coma. This will not, however, help or guide us in the solution of this problem case. Aberrometers cannot measure highly postoperative aberrated eyes properly. Even if possible, the tissue cost with additional laser surgery would be too high. The majority of aberrations are caused by the cornea; it makes more sense to perform a topography-guided surface ablation or a PTK with a smoothing agent. I would not advise to relift the flap for two reasons. First, the quality of the flap is poor. Secondly, there is a higher risk of ectasia when performing additional laser surgery.

My approach includes epithelial removal with PTK, application of mitomycin C3-4 (0.02%) for 30 seconds, irrigation, a short waiting period to allow for diffusion, PRK correction without nomogram adjustment, and a bandage contact lens. I also include a regimen of prednisolone acetate (1%) and ofloxacin (0.03%) five times daily for 1 week (steroid tapered). I will warn the patient that a second treatment is inevitable because of the refractive surprise that arises after this kind of treatment. If this does not work, the final option is a lamellar keratoplasty.

Damien Gatinel, MD
This is a challenging case because of the previous complicated flap relift and severe loss of BCVA. The latter is the most alarming: Persistent low BCVA after spherocylindrical correction contrasts with the moderate elevation of high-order RMS according to the Customvue measurement.

In my experience, such a loss of BCVA on a 5-mm pupil is not induced with 0.6 µm of RMS higher-order aberrations. With the employed Schack-Hartmann aberrometer (Customvue Waveprint, Visx, Santa Clara, California), the underestimation of high-order RMS in this eye with heavily distorted cornea may be the explanation for that discrepancy. Subjective and aberrometer calculated refraction are in relatively good agreement, however, especially for the axis of the cylinder. Significant interface scattering and persistent microfolds may play an additional role in the BCVA reduction. Confirmation of these latter features would orient my therapeutic strategy toward keratoplasty rather than an excimer laser subtraction procedure. I would also perform a complete ocular examination to systematically rule out causes other than corneal for BCVA.

I would not consider any technique incurring relifting the second superficial flap because of both the previous flap relift problems and increased risk of subsequent complications including ectasia, diffuse lamellar keratitis or epithelial ingrowth. Moreover, if the second flap were relifted, the aforementioned possible interface flap microfolds and/or reduced transparency would be increased. Superficial ablation is an alternative, however, there is a risk of severe haze on previously stromal-ablated corneas.

Due to the mixed character of the astigmatism with slight negative spherical equivalent, a pair of arcuate relaxing incisions placed on the steepest meridian (approximately 55?) may also help to reduce the corneal astigmatism. This is my first recommended step. Care should be taken in the incision realization to prevent epithelial ingrowth and perforation. Compromised biomechanics of the cornea may, however, cause poor predictability. If the astigmatism were successfully reduced, the patient would gain additional lines of UCVA and have excess tissue for the following superficial laser ablation. This is my second recommended step. Most of the HOA originates from the cornea, and therefore topography-guided ablation is probably the best option in that case. A topography-guided PRK with the EC-5000 excimer laser (Nidek Inc, Fremont, California), using adjunctive 0.2% mitomycin C for 30 seconds, would then be performed. The parameters of the ablation profile would be determined in the Final Fit Software (Nidek Inc), where optical and transition zone design can be optimized to minimize the depth of ablation. Based on previous successful experience, I would choose the Corneal Wavefront mode with tilt deactivated. My final recommendation is penetrating or deep lamellar keratoplasty, which should only be attempted if the other procedures are ineffective.

A. John Kanellopoulos, MD, is a corneal and refractive surgery specialist. Dr. Kanellopoulos is director of Laservision Eye Institute in Athens, Greece, and practices in New York as well. He is attending surgeon for the department of ophthalmology at the Manhattan Eye, Ear, and Throat Hospital in New York and clinical associate professor of ophthalmology at New York University Medical School. He has no financial interest in any product or company mentioned. Dr. Kanellopoulos may be reached at laservision@internet.gr or +30 21 07 47 27 77.

Erik L. Mertens, MD, FEBO, is a cataract and refractive surgery specialist. Dr. Mertens is medical director of the Antwerp Eye Center, Antwerp, Belgium. Dr. Mertens is a consultant for Bausch & Lomb and STAAR Surgical and he does not have a financial interest in any product or company mentioned. He may be reached at e.mertens@zien.be or +32 3 828 29 49.

Damien Gatinel, MD, is a cataract, corneal and refractive surgery specialist. He is an assistant professor at the Rosthschild Ophthalmology Foundation and Bichat-Claude Bernard Hospital, Paris. Dr. Gatinel does not have a financial interest in any product or company mentioned. He may be reached at gatinel@aol.com or +33 1 48 03 64 86.

Jan 2006