Management of astigmatism in keratoconus with therapeutic refractive surgery
TL;DR
Current therapeutic refractive strategies are best viewed within an individualized, phenotype-driven framework rather than a mandatory linear sequence, and future progress will depend on multimodal imaging, improved phenotyping, and more individualized corneal shape-restoration strategies.
Abstract
Astigmatism is a major determinant of visual impairment in keratoconus (KC), yet in this setting it cannot be understood as a simple cylindrical refractive error. Instead, it reflects a complex optical phenotype generated by anterior and posterior corneal asymmetry, epithelial remodeling, internal optical compensation, and progressive biomechanical instability, often in combination with coma-dominant higher-order aberrations. Beyond reducing monocular image quality, KC-related astigmatism may also compromise binocularity through interocular asymmetry, impaired binocular summation, reduced stereopsis, and visual discomfort. Management therefore depends not only on correcting refractive cylinder, but on distinguishing calculated astigmatic vectors from functionally relevant refractive astigmatism and identifying the relative contributions of irregular corneal optics, including coma, trefoil, and residual low-order error. Measurement remains challenging because corneal and manifest astigmatism frequently diverge, and because results are influenced by centration, analysis zone, device characteristics, and limited repeatability in more advanced disease. Current therapeutic refractive strategies are best viewed within an individualized, phenotype-driven framework rather than a mandatory linear sequence. Corneal collagen cross-linking remains fundamental when progression is present, but has limited refractive predictability. Corneal regularization procedures, including intracorneal ring segments, corneal allogeneic intrastromal ring segments, and customized surface ablation, may be selected when irregular corneal optics are the dominant cause of visual impairment. Once stability and sufficient regularity are achieved, toric phakic intraocular lenses, and in selected cases toric intraocular lenses, can address residual refractive error. Future progress will depend on multimodal imaging, improved phenotyping, and more individualized corneal shape-restoration strategies.