Asymmetric intracorneal ring segments in the treatment of snowman phenotype keratoconus

Keratoconus is a progressive, non-inflammatory disease, resulting in a corneal cone with abnormal thinning and steepening. It causes myopia and irregular astigmatism that cannot be corrected with glasses in moderate and severe cases. The corneal cone can be central, paracentral or pericentral. The topographical abnormality in keratoconus shows different patterns. Fernandez-Vega and Alfonso described asymmetrical types of keratoconus in their latest classification [1]. Snowman phenotype (asymmetric bow-tie) is one of the asymmetrical phenotypes with astigmatic lobes of different size and perpendicular axes of topography and coma.

Intracorneal ring segments (ICRSs) regularize corneal geometry in keratoconus by adding thickness to the periphery and thus, flattening the central cornea [2], [3]. In asymmetric patterns, some parts of the cornea need more flattening, compared to other parts. Therefore, new models with progressive thickness have been designed to customize the corneal effect in asymmetric keratoconus phenotypes. These models have two types with implantation zones of 5 or 6 mm. Their arc-lengths are 160°. The asymmetric segment thickens from one end to the other by 100 μm. Two types can be found in the markets, with thicknesses of 150/250 μm and 200/300 μm.

The study aimed to evaluate refractive, aberrometric, topographic, and topometric outcomes and safety of asymmetric ICRS implantation (Keraring AS) in snowman phenotype keratoconus.

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