In this case, PTK in the right eye to treat idiopathic recurrent corneal erosions resulted in significant anterior stromal haze and a 3.75 D hyperopic shift. The patient has poor quality of vision, with a CDVA of 20/100, and topography shows significant flattening in the central cornea. The most important issues to address are the reason for the induced hyperopia and how to treat the loss of CDVA.
The thickness of Bowman layer is approximately 12 μm; a partial ablation depth between 3 μm and 10 μm is sufficient to achieve healthy migration of the surface epithelium and formation of a new basement membrane. This depth of ablation has no or a minor effect on the refractive error.1 The postoperative pachymetric difference between the 2 eyes in this case is 48 μm, in excess of what is necessary to ablate Bowman membrane. In addition, the circular pattern of the anterior stromal haze corresponds to an ablation width of 6.0 to 7.0 mm. These findings show that during treatment, all ablation was performed directly in the center of the cornea. Creating a wider ablation, performing some ablation in the peripheral cornea, and using an integrated slitlamp on the laser could have avoided the overablation.
The first treatment option in this patient is an RGP contact lens trial for visual rehabilitation. If visual acuity does not improve with the lenses, another excimer laser treatment would be required. The major question is when to correct the residual refractive error. Some prefer to correct the error and the stromal haze during the same session. However, performing PTK alone can significantly improve the refractive error in patients with stromal haze and a refractive shift. I would elect to remove the epithelium with ethanol and perform PTK with MMC 0.02% (0.2 mg/mL) for 2 minutes. The main haze-inhibiting effect of MMC is at the level of blocking keratocyte transformation into myofibroblasts. Mitomycin-C is less effective in producing apoptosis of preexisting myofibroblasts, thereby requiring a longer exposure for therapeutic purposes.2 After the refraction stabilizes, the patient can have another surface ablation for the correction of hyperopia, again with the use of adjuvant MMC. If this approach fails, the patient may be a candidate for femtosecond laser–assisted anterior lamellar keratoplasty for visual rehabilitation.3
1. Rashad KM, Hussein HA, El-Samadouny MA, El-Baha S, Farouk H. Phototherapeutic keratectomy in patients with recurrent corneal epithelial erosions. J Refract Surg. 2001;17:511-518.
2. Netto MV, Mohan RR, Sinha S, Sharma A, Gupta PC, Wilson SE. Effect of prophylactic and therapeutic mitomycin C on corneal apoptosis, cellular proliferation, haze, and long-term keratocyte density in rabbits. J Refract Surg. 2006;22:562-574.
3. Yoo SH, Kymionis GD, Koreishi A, Ide T, Goldman D, Karp CL, O'Brien TP, Culbertson WW, Alfonso EC. Femtosecond laser-assisted sutureless anterior lamellar keratoplasty. Ophthalmology. 2008;115:1303-1307.