Dystrophies of the cornea are primary, bilateral disorders with an underlying genetic cause. The International Committee for Classification of Corneal Dystrophies (IC3D) categorizes the major corneal dystrophies by the corneal layer (ie, epithelial, stromal, or endothelial) most involved and by the identified genetic alterations, when they are known. Thus, the classification system divides major corneal dystrophies into 4 groups:
The dystrophies are described according to a template consisting of clinical, pathologic, and genetic information (see BCSC Section 8, External Disease and Cornea). Although traditional pathologic methods continue to play an important role in the diagnosis of corneal dystrophies, clinicians increasingly rely on ancillary clinical diagnostic modalities, such as confocal microscopy and OCT, because treatment selection depends on the layers and structures involved. Molecular genetic studies are becoming more important in elucidating the pathogenetic mechanisms of corneal dystrophies, for example, the various dystrophies that are now known to be due to a mutation in the transforming growth factor β–induced gene (TGFBI). Such studies have also shown that various corneal dystrophy phenotypes may be caused by mutations in the same gene. Many of these genetic tests are commercially available and can be performed on peripheral blood.
The following subsections cover only the most common corneal dystrophies; see BCSC Section 8, External Disease and Cornea, for additional discussion.
Han KE, Choi SI, Kim TI, et al. Pathogenesis and treatments of TGFBI corneal dystrophies. ProgRetin Eye Res. 2016;50:67–88.
Seibelmann S, Scholz P, Sonnenschein S, et al. Anterior segment optical coherence tomography for the diagnosis of corneal dystrophies according to the IC3D classification. Surv Ophthalmol. 2018;63(3):355–380.
Weiss JS, Møller HU, Aldave AJ, et al. IC3D classification of corneal dystrophies—edition 2. Cornea. 2015;34(2):117–159.
Epithelial and Subepithelial Dystrophies
Epithelial basement membrane dystrophy
Also called map-dot-fingerprint dystrophy, epithelial basement membrane dystrophy (EBMD) is characterized by clinically observed patterns resembling maps, dots, and fingerprints in the superficial cornea. Regional thickening of the epithelial basement membrane with deposition of intraepithelial basal laminar material results in large, slightly gray outlines that look like a continent on a map. Intraepithelial pseudocysts containing degenerated epithelial debris appear as dots. Riblike intraepithelial extensions of basal laminar material give rise to patterns resembling fingerprints (Fig 6-17). EBMD results in focally impaired adhesion of the epithelial basement membrane to Bowman layer. As a result, patients may experience recurrent epithelial erosions. Management includes superficial keratectomy and phototherapeutic keratectomy and is described in BCSC Section 8, External Disease and Cornea.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.