Bilateral Excimer Laser-Assisted Penetrating Keratoplasty for Genetically Verified Autosomal Recessive Cornea Plana (CNA2) – Ultrastructural and Immunohistochemical Findings

Introduction

Cornea plana (CP) is a rare congenital disorder, characterized by a bilaterally flattened corneal curvature, limbal anomalies with early-onset arcus lipoides and corneal opacities of variable extend [1]. The more frequent and more severe autosomal recessively inherited subtype of CP (CNA2; MIM #217 300) is caused by various homozygous mutations in the KERA-gene (chromosome 12q21) [2]. KERA encodes keratocan, a predominantly in the cornea occurring core protein of proteoglycans, which contributes to corneal fibrillogenesis and is believed to be important for the formation and maintenance of the corneal curvature [2]. The autosomal dominant subtype of CP (CNA1; MIM #121 400) with less severe corneal flattening is considered to occur much rarer [3].

In CNA2, the corneal radius of curvature converges almost to that of the sclera, which reduces the corneal refractive power to about 25 to 35 Diopters (> 35 D in the milder CNA1 subtype), resulting in high refractive hyperopia and usually major amblyopia [4], [5]. The expanded limbal zone and early-onset arcus lipoides may create the appearance of a pseudo-microcornea, but the corneal diameter is usually not reduced [6]. Further ocular malformation is not common. Despite the corneal flattening, axial length of the globe is reported to be regular in most cases [7]. There is a risk of disease progression during lifetime that manifests as a slow central spread of the peripheral stromal opacity, endothelial decompensation or narrow-angle glaucoma [1], [4], [8].

Management of CP is currently focused on non-surgical correction of the refractive error and glaucoma monitoring. Surgical approaches are reported very rarely and are usually declined due to the difficult situs [1], [4], [9]. This case report presents successful excimer laser-assisted penetrating keratoplasties (excimer-PKP) in two eyes with severe CNA2 and chronic corneal edema, in one eye with simultaneous open-sky cataract surgery (Triple Procedure) as well as subsequent Descemetʼs membrane endothelial keratoplasty (DMEK).

Due to the rare availability of explanted tissue, no histopathological studies on CNA2 are available to date. This report is the first to present such, in the form of light and electron microscopic findings as well as keratocan-immunostaining of genetically confirmed CNA2.

Publication History

Received: 13 April 2025

Accepted: 22 June 2025

Article published online:
01 September 2025

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