Corneal crosslinking: Stabilization or rehabilitation?
Corneal crosslinking: Stabilization or rehabilitation?
复制标题
角膜交联：稳定还是康复？
DOI：
10.1016/j.jcrs.2018.05.005
复制
发表时间：
2018
影响因子：
2.8
通讯作者：
DuppsJr,WilliamJ
中科院分区：
文献类型：
--
作者：
DuppsJr,WilliamJ
Keratoconus and other ectasias are, fundamentally, disorders of refractive error. Since management options span the entire spectrum of anterior segment surgery, these conditions do not respect traditional disciplinary lines between the refractive surgeon, the cataract surgeon, and the corneal transplant surgeon. Corneal crosslinking (CXL), phakic IOL implantation, lens extraction with toric lens implantation, small aperture sulcus implants, intracorneal implants, photorefractive keratectomy (PRK), transepithelial photorefractive keratectomy (PTK), deep or penetrating keratoplasty, and combinations of the above are all employed in the management of ectasia. For this reason, patients are likely to achieve the best outcomes when a crossdisciplinary approach to treatment is emphasized. Corneal crosslinking has become an indispensable tool in the treatment of ectasia. One important and practical question that is particularly salient outside the United States relates to the purpose of treatment: Is the treatment goal optical rehabilitation or disease stabilization? Clearly, both are desirable outcomes. But questions remain as to how to best combine these goals in a CXL treatment plan so visual improvement can be maximized without compromising the goal of long-term disease stabilization. The answers to those questions impact which treatments should be selected, how they should be performed, when they should be offered, and to whom they should be recommended. To form an approach to addressing these questions, it is helpful to first focus on the mechanisms of vision loss and corneal shape instability in ectasia then unpack some operating principles for understanding and leveraging the effects of CXL. To the first point, it is useful to understand ectasia as a spatially inhomogeneous corneal biomechanical weakening process that can involve intrinsic (ie, genetic, biochemical) and/or extrinsic (ie, surgical, eye rubbing) risk factors. The primary factor limiting visual quality of life in most ectasia patients is irregular astigmatism, especially the coma components, that arises from inhomogeneous weakening. While lower-order aberrations (LOAs) can account for significant visual blur in ectasia patients, they are readily addressed with spectacles, soft contact lenses, and surgical approaches that correct sphere and regular astigmatism. It is the spatial inhomogeneity of the stromal weakening process that causes a change in the distribution of strain in the cornea. Weaker areas of the stroma are less able to resist the outwardly directed force of intraocular pressure (IOP) than stronger areas. In the conservation of energy demanded by Newtonian physics, this causes a disproportionate outward bending of the weakest area and produces a steep irregular topographic feature that is the sine qua non of corneal ectasia. Localized corneal thinning is an important clinical feature of corneal ectasia, but experimental and computational studies support the idea that weakening may be the primary factor driving the topographic manifestations of ectasia. 1–3 Furthermore, modeling suggests that the relationship between progression of weakening and progression of corneal steepening is not linear, but exponential. 1 Thus, early stromal weakening may produce relatively slow changes in corneal curvature that make shape-based detection of early disease challenging, and substantial weakening may already be present before curvature begins to inflect noticeably upward. Building on this foundation, certain clinical and experimental observations can serve as operational principles for a rational approach to explaining corneal shape responses to CXL and informing our thinking on …
