Posterior polymorphous corneal dystrophy (PPCD; sometimes also ''Schlichting dystrophy'') is a type of corneal dystrophy, characterised by changes in
Descemet's membrane
Descemet's membrane ( or the Descemet membrane) is the basement membrane that lies between the corneal proper substance, also called stroma, and the endothelial layer of the cornea. It is composed of different kinds of collagen (Type IV and VIII ...
and
endothelial layer. Symptoms mainly consist of decreased vision due to corneal edema. In some cases they are present from birth, other patients are asymptomatic. Histopathological analysis shows that the cells of endothelium have some characteristics of epithelial cells and have become multilayered. The disease was first described in 1916 by Koeppe as ''keratitis bullosa interna''.
Genetics
PPCD type 2 is linked to the mutations in
COL8A2
Collagen alpha-2(VIII) chain is a protein that in humans is encoded by the ''COL8A2'' gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA th ...
, and PPCD type 3 mutations in
ZEB1
Zinc finger E-box-binding homeobox 1 is a protein that in humans is encoded by the ''ZEB1'' gene.
ZEB1 (previously known as TCF8) encodes a zinc finger and homeodomain transcription factor that represses T-lymphocyte-specific IL2 gene expression ...
gene, but the underlying genetic disturbance in PPCD type 1 is unknown.
Pathophysiology
Vacuoles are demonstrated in the posterior parts of the
cornea
The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...
. The vesicles are located on the endothelial surface. The corneal endothelium is normally a single layer of cells that lose their mitotic potential after development is complete. In posterior polymorphous corneal dystrophy, the endothelium is often multilayered and has several other characteristics of an epithelium, including the presence of desmosomes, tonofilaments, and microvilli. These abnormal cells retain their ability to divide and extend onto the trabecular meshwork to cause
glaucoma
Glaucoma is a group of eye diseases that can lead to damage of the optic nerve. The optic nerve transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of ...
in up to 40% of cases.
Diagnosis
See also
*
Corneal dystrophy
Corneal dystrophy is a group of rare hereditary disorders characterised by bilateral abnormal deposition of substances in the transparent front part of the eye called the cornea.
Signs and symptoms
Corneal dystrophy may not significantly affect ...
References
External links
*
{{Human corneal dystrophy
Disorders of sclera and cornea