Lattice dystrophy

There are 4 types, which vary by age at presentation, corneal morphology, and location of the corneal deposits:

• type I, the most common form and the earliest in age of onset
• type II, a form with systemic repercussions, with deposits that are more peripheral and less numerous than in type 1.
• type III a
• later age of onset, after 40 years.
• deposits that are larger than in type 1 and deeper, reaching the mid stroma, extending from limbus to limbus
• type IV, nodular deposits that are larger than in type 1 and reach the deep stroma. This variant is often unilateral or bilaterally asymmetric. Older age, around 40-50 years

Lattice dystrophy type I: Biber-Haab-Dimmer

Genetics

AD Autosomal dominant (AD)

Mutation

TGFBI, including L518P

Laterality

bilateral

Symmetry

Yes

Systemic factors:

Age of onset

during childhood; the cornea is normal at birth, 1st and 2nd decade.

Location

Bowman layer and anterior stroma.

Appearance:

Direct illumination

refractile branching linear deposits within the stroma, with whitish subepithelial ovoid deposits early in the dystrophy and a stroma that is initially clear between the deposits. As the disease progresses, a diffuse anterior stromal haze appears, sparing the corneal periphery. The lines begin centrally and superficially and progress in a centripetal manner and into deeper layers.

Retroillumination

the best way to see the amyloid deposit lines.

Cobalt blue

the refractile deposits may be autofluorescent.

Pain or recurrent erosion

Yes; the erosions may take on a dendritic/pseudodendritic appearance.

Visual acuity

decreases as the dystrophy progresses, owing to the stromal haze and epithelial irregularity.

Diagnosis:

• Histology: amyloid deposits in the subepithelial region and mainly in the anterior stroma. It is this subepithelial deposit that disrupts the bond between stroma and epithelium, resulting in recurrent erosions. The deposits stain with Congo red and are birefringent and dichroic under polarized light. Periodic Acid Schiff (PAS) staining positive.
• Electron microscopy: extracellular fibrillar deposits measuring 8 to 10 microns, randomly aligned.
• Confocal microscopy: hyperreflective branching linear images reminiscent of fungal infections or even of the corneal deposits seen in monoclonal gammopathies. The subepithelial nerve plexus is less dense than normal, with reduced corneal sensitivity.
• OCT: the deposits are hyperreflective and poorly defined, and the stromal surface is irregular and wavy

Recurrence +++ Recurrence on the graft: Frequent (indeed the most frequent of the stromal dystrophies). The mean time to recurrence is 9 years.

Lattice ≈ 9 years > granular > macular ≈ 15 years

Lattice dystrophy type II: Meretoja syndrome — currently no longer considered a dystrophy, since it is a systemic disorder.

Genetics

AD Autosomal dominant (AD)

Mutation

9p34, gelsolin

Laterality

Bilateral

Symmetry

Yes

Systemic factors

mask-like facies, blepharochalasis, pendulous ears, peripheral facial nerve palsies, and dry, lax skin.

Age of onset

3rd and 4th decade, associated with systemic amyloidosis.

Location

Bowman layer and anterior stroma.

Appearance:

Direct illumination

the reflective linear deposits are less numerous and more peripheral; they begin at the periphery and extend centripetally from the limbus but rarely reach the center of the cornea. Reduced corneal sensitivity

Pain or recurrent erosion

rare

Visual acuity

preserved for a long time.

Diagnosis:

• Histology: lattice-type amyloid deposits in discontinuous bands beneath Bowman layer. The deposits are secondary to the gelsolin mutation and do not correspond to AA and AP type amyloid. These deposits are also present in the sclera, conjunctiva, ciliary body, choroid, ciliary nerves and vessels, as well as the optic nerve. In addition, they may be present in the walls of vessels, the peripheral nerves, and the glomeruli.
• Confocal microscopy: fibrillar deposits along the basal epithelial cells and the corneal nerves.

Recurrence +++ Recurrence on the graft: Frequent (indeed the most frequent of the stromal dystrophies). Mean time to recurrence: lattice > granular > macular.