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Consultation section

May consultation #2

Shousha, Mohamed Abou MD

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Journal of Cataract & Refractive Surgery: May 2010 - Volume 36 - Issue 5 - p 867-868
doi: 10.1016/j.jcrs.2010.03.004
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This patient presents with poor vision, subepithelial scarring, and hyperopic anisometropia secondary to PTK performed for recurrent epithelial erosions. The slitlamp photograph shows central subepithelial haze. On corneal topography, there is irregularity attributable to the subepithelial scarring and, most important, central corneal flattening consistent with the previous PTK. The affected cornea is 48 μm thinner than that in the fellow eye. Assuming that the 2 eyes had the same pachymetry, one could conclude that the ablation depth of the PTK was approximately 48 μm. The deep PTK ablation, together with the subepithelial scarring, explains the hyperopic anisometropia. Phototherapeutic keratectomy for recurrent epithelial erosions typically uses superficial ablation (5 to 7 μm). Reviewing the medical records might explain why the surgeon aimed for such an unusually deep ablation.

A rigid gas-permeable (RGP) contact lens over-refraction would help determine the major contributor to the patient's poor vision. I do not think this would improve her vision much, confirming that haze, not topography, is the greater contributor to the poor CDVA. In this case, an RGP lens could be ruled out as an option to rehabilitate the patient's vision and a more invasive intervention would be warranted.

An appealing option is combined PTK and PRK with adjunctive mitomycin-C (MMC). First, the surgeon must explain to the patient that the main goal of the intervention is to regain corneal clarity and that even though a refractive correction would be attempted, a residual refractive error is possible. The patient must understand that despite measures taken to minimize the risk for haze recurrence, the possibility cannot be eliminated. Measuring the depth of the corneal scar preoperatively by anterior segment optical coherence tomography will allow accurate programming of the laser machine. I would use alcohol 20% for epithelial debridement and because it would be hyperopic PRK, would not touch the central cornea. First, PTK laser pulses with a masking agent (balanced salt solution) would be applied to remove the central scar and smooth the surface. Next, I would perform PRK to correct most of the hyperopic anisometropia.

I would treat the entire preoperative hyperopia. More hyperopic PRK could be attempted depending on the depth of the second PTK. The amount of PTK-induced hyperopia depends on many factors, such as the laser platform (broad beam versus flying spot), ablation profile (size, asphericity, blend zone) and, most important, the amount of masking agent used. Because of these factors, the prediction of PTK-induced hyperopia would be based more on an individualized surgeon's nomogram. At the end of surgery, I would apply MMC 0.02% for 45 seconds to decrease the risk for haze recurrence. Postoperatively, I would fit a bandage contact lens until complete reepithelialization. I would prescribe profuse lubrication to optimize the ocular surface and a slow steroid taper to prevent haze formation.

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