Stromal Dystrophies Lattice

There are three major types of lattice dystrophy and all are unified by the appearance of lattice lines on slit-lamp examination and amyloid deposition on histological examination.

Lattice type 1. In type 1 lattice, or Biber-Haab-Dimmer corneal dystrophy, amyloid is deposited in the cornea but is not found elsewhere in the body. It can vary in its appearance, and there is often progression from round, ovoid and white, or small, filamentous, and refractile anterior stromal lesions to more nodular, threadlike, and thicker linear lesions that extend into deep stroma (Figure 2(a)). Initially, the stroma between lesions remains clear, but over time these spaces opacify and assume a ground-glass appearance. The limbus is typically spared. Signs of lattice dystrophy most often appear in early childhood, but symptoms of surface erosions, irregular astigmatism, and vision loss usually begin in the second or third decades of life.

Recurrent erosions can be frequent and can be managed as described previously. Some authors believe that phototherapeutic keratectomy should be avoided (as well as laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK)) because excimer laser, within the UV light spectrum, may trigger activation of TGFB and exacerbate this condition. For severe vision loss due to opacification, penetrating and lamellar keratoplasty may be warranted. Recurrence may occur in these grafts but presents differently than the primary lesions.

Specimens are positive for amyloid and stain with Congo red, periodic acid-Schiff’s reagent (PAS), Masson’s trichrome, and thioflavine-T fluorochrome, and are metachromatic with crystal violet (Figure 2(b)). As with all amyloid, they demonstrate apple-green birefringence under polarized light.

Lattice type 2. Type 2 lattice, also known as Meretoja’s, familial, or Finnish amyloidosis syndrome, is characterized by both systemic and corneal amyloid deposition. Typically seen in families of Finnish, European, or Japanese origin, it is usually asymptomatic until early adulthood.

Figure 2 (a) Slit-lamp photograph of lattice type 1 dystrophy. Arrow indicates amyloid deposition. (b) Congo red stain of cornea in lattice type 1 demonstrating amyloid deposition. Afshari, N. A., Mullally, J. E., Afshari, M. A. et al. (2001). Survey of patients with granular, lattice, avellino, and Reis-Bijcklers corneal dystrophies for mutations in the BIGH3 and gelsolin genes. Archives of Ophthalmology 119:16-22. © 2001 American Medical Association. All rights reserved.

Corneal slit-lamp examination shows more peripheral deposits, with fewer and finer lattice lines, and a primarily sub-Bowman’s location of deposition.

Patients begin to experience corneal changes in the third decade of life, but symptoms of reduced corneal sensation and frequent recurrent erosions are uncommon until the fifth decade. Overall, the visual prognosis is better than in type 1 with many patients not developing visual loss until late in the course of disease. While there is a decreased severity of corneal disease, the systemic manifestations can be serious and include dry, itchy skin, intermittent proteinuria, and cardiac abnormalities. Patients may develop severe mask-like facial paresis (loss of facial Muscle motor function), blepharochalasis (inflammation of eyelid), protruding lips, and pendulous ears from amyloid deposition and secondary muscular dysfunction.

Unique among the lattice dystrophies, type 2 does not arise from a mutation in the TGFBI gene. Instead, it has been linked to a dominant mutation of the gelsolin gene on 9q32-34 that encodes an amyloid precursor.

Lattice types 3 and 3a. Type 3 lattice is the least severe and has an autosomal recessive pattern of inheritance. The lattice lines in type 3 are thicker and ropier in appearance, and later in onset. Vision is often not affected until the sixth or seventh decade of life, and recurrent erosions are rare. Like type 1, type 3 is associated with a defect in the TGFBI gene. Type 3a is similar in presentation to type 3 but follows an autosomal dominant inheritance pattern.

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