Optical coherence tomography-guided decision-making for Descemet stripping automated endothelial keratoplasty in Ahmed glaucoma valve-related corneal decompensation.

Regular astigmatism is a common, treatable refractive error caused by a stronger power in one meridian [,], leading to an asymmetric refraction of light rays []. Uncorrected astigmatism negatively affects patients’ vision-related quality of life by increasing glare and haloes, impairing night-driving visibility, and increasing the risk of falls or physical injury []. Prolonged vision impairment can lead to significant eyestrain and headaches for patients, increasing the difficulty of everyday activities and negatively affecting professional life []. Surgical correction of astigmatism offers powerful corrective potential, restoring vision quality and greatly improving the patient’s quality of life [-]. Classified by source, astigmatism can be corneal, lenticular, or retinal []. Corneal astigmatism is the most common form of astigmatism and is secondary to abnormalities in the anterior and/or posterior corneal curvature [,]. Curvatural lenticular astigmatism originates from abnormalities of the crystalline lens shape, such as in lenticonus [,]. Positional lenticular astigmatism is caused by tilting or displacement of the lens (subluxation) [], such as encountered in ectopia lentis and/or Marfan Syndrome [,]. Lenticular index astigmatism is caused by progressive variations in the refractive lens index [,-]. Retinal astigmatism is rare and originates from oblique placement of the macula [], such as in retinopathy of prematurity [] or after traditional scleral-buckling surgery of retinal detachment []. Classified by type, astigmatism can be regular when there is a single higher-power refractive meridian or irregular when there are several meridians of different refractive strengths and orientation in degrees [,]. Regular astigmatism is commonly subclassified by orientation of the higher-power meridian into with-the-rule (60-120°, WTR astigmatism) [], against-the-rule (0-30° or 150-180°, ATR astigmatism) [], and oblique astigmatism (between 30-60° and 120-150°) []. Irregular astigmatism is most commonly corneal in origin and thus often associated with the evolution of corneal conditions such as keratoconus, where the corneal shape changes from a physiological orthogonal shape to non-orthogonal with a dramatic increase in higher-order aberrations (HOAs) []. Irregular astigmatism cannot be fully corrected using cylindrical spectacle lenses and requires use of specialized contact-lenses such as in keratoconus management (rigid corneal, soft, hybrid or piggyback systems – rigid corneal lens fitted over a soft contact lens) [] or refractive surgery (corneal topography-guided [] or via toric intraocular lens implantation [,] which can also be combined with adjuvant corneal treatment for other significant meridians via femtosecond laser-assisted astigmatic keratotomy (FSAK) [].