Surprising astigmatism hypercorrection after corneal ring segments implantation in keratoconus treatment after 8 years of follow up

Objective: To report a case of hypercorrection of astigmatism (Cyl) after implantation of 2 segments of short arch ring for keratoconus treatment and to describe its replacement by long arch segment. Methods: This is a case report of a patient with keratoconus and no adaptation to glasses or contact lenses, who was implanted 2 ring segments: upper nasal (155º/ 200μm) and inferior temporal (155º/ 250μm). Results: First postoperative month: CVA = 20/ 50 (-10.50-2.50x135°) and SimK K1 = 48.4x143° and K2 = 51.2x53° (Cyl 2,8D). In the 3rd year: CVA 20/ 30 (-6.00-2.50x135º), with inversion of the axes: K1 = 49,5x60º and K2 = 52,0x150º (Cyl 2,6D). The hypercorrection increased up to the 8th year: CVA = 20/40 (-4,50-6,00x75º) and SimK 47,8x51º/ 60,4x141º (Cyl 12,6D). The 2 segments were replaced for a single segment (320º/ 300μm) and after 1 month: CVA = 20/ 25 (-5,75 spherical) with SimK 46,8x38º/ 48,9x128º (Cyl 2,1D). Conclusion: The ring aims to flatten the most curved meridian, but surpassing the previous value induces astigmatism in the opposite meridian. The hypercorrection of the 2 short segments must occur due to its movement of the extremities, which does not occur with the single long arc segment (≥ 300º). Abbreviations: CVA = Corrected visual acuity, SimK = Simulated keratometry, LE = Left eye, RE = Right eye