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Corneal refractive surgery in keratoconus.

W. Dupps

Published 2020 in Journal of cataract and refractive surgery

ABSTRACT

The scenario is common. A patient comes to your office with high hopes of scheduling a surgery that can offer spectacle or contact lens independence and then is told for the first time that they have keratoconus. This news comes unexpectedly and has multiple layers of impact for the unsuspecting patient, who hears in rapid succession the following bits of information: (1) you are not a candidate for laser refractive surgery, (2) in addition to that disappointing news, you have a progressive corneal disease that could lead to loss of vision even with spectacles or contact lenses, and (3) finally, some good news: a treatment is available, corneal crosslinking (CXL), and it offers a high likelihood of stabilizing (but not necessarily improving) this condition. At this point in the visit, the patient likely has not suddenly forfeited their desire to reduce their dependence on spectacles or contact lenses. In fact, many keratoconic patients who are diagnosed during a refractive surgery screening examination originally schedule their consultations because they are aware that their visual quality is suboptimal in spectacles or contact lenses and they hope that laser refractive surgery might be able to rectify their vision. The question of whether corneal refractive surgery can be performed after CXL therefore flows naturally from the patient’s underlying motivations and is a logical extension of our explanation of how CXL works. If CXL increases the biomechanical strength of a pathologically weakened cornea, then why would not laser refractive surgery become an option? Given that keratoconus has significant adverse effects not only on vision but also on quality of life, we share the patient’s goal of trying to improve vision, not merely stabilize it, and we are sympathetic to the question. However, the conscientious refractive surgeon instinctively recoils at the idea of performing ablative corneal surgery in the setting of ectatic disease. The primary risk factor for postrefractive surgery ectasia is topographic evidence of keratoconus, and the prospect of performing any procedure that involves tissue incision or removal carries a risk of further destabilization. Even if we could assume that CXL fully restores the normal biomechanical state of the keratoconic cornea, the prospect of performing a subsequent ablative procedure is troubling because it would involve removing tissue that was specifically stiffened to achieve corneal shape stability. Would not this directly undermine the purpose of CXL in such patients? In an attempt to balance the goal of visual rehabilitation with the concern of destabilization, several studies have explored sequential, same-day excimer laser treatment followed immediately by CXL. There is an inherent advantage in combining the time-tested stiffening efficacy of an epithelium-off CXL procedure with a rehabilitative procedure such as transepithelial phototherapeutic keratectomy (PTK) or photorefractive keratectomy (PRK) that also requires removal of the epithelium. This approach nullifies the need to debride the epithelium again for PRK at a later date and avoids any potential related complications of a second epithelial defect. And, as noted earlier, there is a strong rationale for performing CXL as the final step in the procedure to avoid ablation of the crosslinked stroma. The variety of approaches has taken many forms, including but not limited to the following, which have been published with at least 12 months of follow-up data:

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