Lattice Corneal Dystrophy

Excerpt

Lattice corneal dystrophy (LCD) is an inherited disorder of the eye characterized by the deposition of amyloid resulting in steadily progressive loss of vision. These deposits create linear, “lattice-like” opacities arising primarily in the central cornea, while the peripheral cornea is often spared. They are radially oriented and are accompanied by gradual, superficial opacification of the cornea. Recurrent epithelial erosions are often present, causing ocular irritation and additional vision loss. The erosions may appear before any noticeable stromal deposits. LCD belongs to a broader family of corneal dystrophies and has several subtypes, as described below.

Type I LCD (LCD1), also known as classic lattice corneal dystrophy or Biber-Haab-Dimmer dystrophy, is the primary form of LCD. It is autosomal dominant and results from mutations in the transforming human growth factor beta-induced (TGFBI) gene. Although TGFBI and its protein transcript are found throughout the body, there are no known systemic effects outside of the ocular pathology for which it is named. It usually presents in the first or second decade of life.

The LCD variants are subtypes of LCD caused by a variety of mutations on the TGFBI gene. The variants were formerly described as types IA, III, IIIA, IIIB, IV, V, VI, VII, and polymorphic corneal amyloidosis. These are variations of the same disease process that causes type I LCD, with minor changes in their phenotypic features. Specific phenotypic patterns are traceable to specific mutations in the TGFBI gene, which resulted in their being initially described as separate diseases. They are now considered to be subtypes of the same disease, in which type I is the classic and most common presentation. The variants are often geographically specific and are occasionally traceable to single founder mutations.

LCD type II is no longer included among the corneal dystrophies as it is a primarily systemic disorder with ophthalmologic features. While it was initially included in the LCD family because of the lattice-like ocular deposits, it is now more accurately described as familial amyloid polyneuropathy (FAP) type IV, FAP Finnish type, FAP Gelsolin type, or Meretoja syndrome. Systemic symptoms include neuropathy (due to amyloid infiltration of nerves), facial paralysis, and extreme skin laxity. It tends to present in the twenties.

Another disease process often mistakenly included in the LCD family is granular corneal dystrophy type II (GCD type II). Also called combined granular-lattice dystrophy or Avellino dystrophy, GCD type II was formerly considered a hybrid of granular and lattice dystrophies since it exhibits symptoms of both diseases. It is characterized by both granular and branching linear deposits that make it challenging to distinguish it from the LCDs. Physical exam findings that differentiate it from the lattice dystrophies are further discussed in this article under the name Avellino dystrophy, to minimize confusion with type II LCD.