Corneal dystrophies are a group of inherited disorders characterized by loss of corneal transparency that affect different layers of the cornea. They are typically bilateral although onset may be sequential or asymmetric. The International Committee for Classification of Corneal Dystrophies (IC3D), Edition 2, proposed a modified anatomic classification consisting of (1) epithelial and subepithelial dystrophies, (2) epithelial–stromal transforming growth factor-induced (TGFBI) dystrophies, (3) stromal dystrophies, and (4) endothelial dystrophies (▶ Table 5.1).

5.1.1 Epithelial and Subepithelial Dystrophies

Epithelial basement membrane dystrophy (EBMD), also known as map-dot-fingerprint dystrophy, usually develops between the ages of 20 and 40 years. It is characterized by grayish epithelial fingerprint lines, dots (microcysts), and geographic maplike lines. Although it is usually asymptomatic, approximately 10% of patients develop painful, recurrent epithelial erosions and decreased vision. In some families, EBMD appears to segregate as an autosomal dominant (AD) disorder and point mutations in the TGFBI gene have been identified. EBMD is, however, present in up to 76% of persons over the age of 50 years, suggesting that most cases of this condition represent age-dependent degeneration of the cornea.

Meesmann’s corneal dystrophy is a slowly progressive corneal dystrophy with early childhood onset, which presents with multiple, small epithelial vesicles that extend to the limbus (▶ Fig. 5.1). These are most numerous in the interpalpebral area. Coalescence of cysts may result in refractile linear opacities with intervening clear cornea. Corneal thinning and hypoesthesia may also be found. In the Stocker–Holt variant, the whole cornea shows fine grayish punctate, epithelial opacities that stain with fluorescein and linear opacities that may adopt a whorl pattern. Patients are usually asymptomatic, although some may have mild visual reduction, glare, photophobia, and recurrent painful punctiform epithelial erosions.

5.1.2 Epithelial–Stromal TGFBI Dystrophies

Symptoms of patients with Reis–Bücklers corneal dystrophy (RBCD) include painful recurrent corneal erosions and impaired vision, starting in the first decade of life. While recurrent corneal erosions tend to decrease with time, vision slowly deteriorates. In the early stages, discrete confluent irregular geographic-like opacities with varying densities develop at the level of the Bowman layer and superficial stroma. Subsequently, opacities extend to the limbus and deeper stroma.

Thiel–Behnke corneal dystrophy (TBCD) is also called corneal dystrophy of Bowman’s layer type II, honeycomb-shaped corneal dystrophy, anterior limiting membrane dystrophy type II, and curly fiber corneal dystrophy. TBCD is an AD form of corneal dystrophy characterized by progressive honeycomb-like, subepithelial corneal opacities with recurrent erosions. It can be difficult to distinguish TBCD from RBCD in early or individual cases. In the early stage, RBCD shows more irregular diffuse opacities with clear interruptions, whereas TBCD exhibits multiple flecks with reticular formation. RBCD tends to have a more aggressive course. In patients with TBCD, the symptoms start at the first and second decades with painful recurrent corneal erosions. Gradually erosions become less frequent and characteristic solitary flecks or irregularly shaped scattered opacities at the level of the Bowman layer appear, followed by symmetrical subepithelial honeycomb opacities (▶ Fig. 5.2). The onset of visual impairment is noted at the second decade of life and gradually progresses, resulting from increase of corneal scarring. The peripheral cornea typically is not involved, but in older patient, opacities can progress to deeper stromal layers and affecting the corneal periphery. Anterior segment optical coherence tomography (OCT) demonstrates the sawtooth pattern of hyper-reflective material in the Bowman layer in patients with TBCD.

Granular corneal dystrophy type 1 (GCD1), also called corneal dystrophy Groenouw type I, is characterized by multiple stromal opacities. Symptoms start as early as the age of 2 years. The initial symptoms are glare and photophobia. Visual acuity decreases as opacification progresses with age. Recurrent erosions are seen frequently. In children, a vortex pattern of brownish granules superficial to the Bowman layer can be observed. In later stages, well-defined granules appear white on direct illumination with clear intervening stroma (▶ Fig. 5.3). The size and number of granules increase, resulting in a “snowflake” appearance. On retroillumination, these granules are composed of extremely small, translucent dots that have been described to resemble vacuoles, glassy splinters, or crushed bread crumbs. Opacities do not extend to the limbus. In later life, granules extend into the deeper stroma approaching Descemet’s membrane. With progression, opacities become more confluent in the superficial cornea and reduce visual acuity.

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