Posterior amorphous corneal dystrophy

History

Recently reclassified from a category 3 dystrophy to a category 1 dystrophy

Genetics

AD

Mutation

Heterozygous deletion on chromosome 12q21 of a cluster of genes: keratocan, lumican, decorin, and epiphycan, which are small leucine-rich proteoglycans involved in collagen and extracellular matrix synthesis.

Laterality

Bilateral

Symmetry

Yes

Associated factors

Rare; anterior segment anomalies: corectopia, pseudopolycoria, iridocorneal adhesions, a prominent Schwalbe line but no glaucoma. Thin cornea and flatter than normal keratometry (hyperopia).

Age of onset

The abnormality is present from birth but is rarely diagnosed, since the majority of patients are asymptomatic.

Location

The posterior stroma

Appearance:

Direct illumination

incomplete or complete gray lamellar opacities of the posterior stroma, often involving the peripheral cornea but sometimes extending from limbus to limbus. These opacities are separated by clear intervals.

Pain or recurrent erosion

No

Visual acuity

Usually preserved; patients are often asymptomatic.

Diagnosis:

• Histology: irregular posterior stromal lamellae with the presence of extracellular material that takes up colloidal iron staining (mucopolysaccharides and glycoproteins). An interruption of Descemet membrane by collagen fibers and cystic membranous abnormalities of the endothelial cells is possible.
• Electron microscopy: disorganization of the posterior stromal lamellae with interruption of Descemet membrane by a fibrillar layer.
• Confocal microscopy: hyperreflective posterior stroma with microfolds.