I. Biomicroscopic Examination Techniques for Best Viewing of Corneal Opacities
A.Diffuse Illumination
1.How many and what type of opacities
B.Parallelpiped
C.Optic Section
1.What layer(s) of the cornea are involved
D.Indirect illumination
E. Retroillumination
1.Are more opacities visible
II.Features of Corneal Dystrophies and Degenerations
A. Corneal Degenerations
1.A deposition of abnormal elements due to corneal cellular changes
2.Signifies a degradation, deterioration, change in structure, secondary
inflammation, metabolic change, aging
III.Characteristics of Corneal Dystrophies
A. Inherited, usually autosomal dominant Bilateral and symmetric (may be asymmetric)
B. Present early with central changes
C. Not associated with prior inflammation and rarely with systemic disease
D. No corneal vascularity expected
E. May be stationary or slowly progressive
IV.Epithelial Dystrophies
A. Map-Dot-Fingerprint Dystrophy
1. Most common anterior dystrophy
2. Maplike, dot-like (microcysts), fingerprint and bleb (putty) opacities
3. Painful recurrent epithelial erosions after 3rd decade
B. Meesman’s Dystrophy
1. Opacities consist of epithelial uniform grey-white microcysts seen early in life
2. Microcysts contain intracellular keratin; recurrent corneal erosions
3. Linkage studies identify mutations in two cornea-specific genes
C. Band-Shaped/Whorled Microcystic Dystrophy (Lisch)
1. Grey band-shaped, feathery opacities made up of densely crowded microcysts.
2. Linkage of the gene maps to the X chromosome
V.Bowman’s Layer Dystrophies
A.Reis-Buckler’s Dystrophy
1.Ring-shaped opacities confined to Bowman’s membrane
2.Thickened epithelium-Irregular astigmatism, RCEs
3.Mutation maps to the keratoepithelin gene (BIGH3) on chromosome 5
VI. Stromal Corneal Dystrophies
A.Granular Dystrophy
1. Common stromal dystrophy
2. Opacities consist of white, round, crumb-like spots and/or rings
3. Good visual acuity until 7th or 8th decade when spots coalesce and stroma
between the spots is affected
4.Opacities consist of an eosiniphilic hyaline type deposition
5.Do well with PTK when VA deteriorates
6.Mutuation localized to the BIGH3 gene on chrom 5(5q31)
B.Lattice Dystrophy Type I
1.Opacities consist of thin, translucent lines composed of amyloid
2.Good vision until later in life-may need PK
3.Is bilateral, but can be asymmetric and unilateral
4.Epithelial erosions can occur
5.Mutation localized to the BIGH3 gene (5q31)
C. Lattice Dystrophy Type II
1.Associated with systemic amyloidosis
2.Deposition of amyloid in many tissues including skin, arteries, sclera
3.Corneal changes occur later in life
4.Mutation localized to the gelsolin (GSN) gene on chromosome 9 (9q34)
D. Late-Onset Lattice Dystrophies
E..Combined Granular and Lattice Dystrophy (Avellino Dystrophy)
1.Granular and lattice type changes in the same eye
2.Hyaline and amyloid deposits in stroma
F. Macular Dystrophy
1.Autosomal recessive, early onset; VA severely affected
2.Characterized by stromal haze, and milky white opacities
3.Mutation localized to the 123 gene on chromosome 16 (16q22)
I.Central Crystalline Dystrophy of Schnyder
1.Characterized by central crystalline stromal cholesterol deposits possible arcus
2.Rule out hyperlipidemia
5.Mutation localized to chromosome 1 (1p34-36)
J. Fleck Dystrophy
1.Opacities consist of small, fine dandruff-like particles in the stroma
2.Visual acuity good throughout life since stroma between flecks remains clear
K.Central Cloudy Dystrophy
1.Central opacity in stroma looks like cracked-ice or crocodile skin
2.Appearance similar to crocodile shagreen,
VII.Endothelial Dystrophies
A.Fuch’s Dystrophy
1.Characterized by three stages
2.Results in corneal edema, usually greatest upon awakening
3.Affects older individuals, greater than 40 years
4.If edema is present, treat with hyperosmotic agents
B.Posterior Polymorphous Dystrophy
1.Isolated and coalesced posterior vesicles
2.Wide areas of thickening of Descemet’s membrane
3.Corneal edema and peripheral anterior synechiae
4.Treatment similar to Fuch’s dystrophy
5.An unidentified gene has been mapped to the 20q11 locus of chromosome 20
C.Congenital Hereditary Endothelial Dystrophy (CHED)
1.CHED 1
a. Autosomal dominant, edema a few years after birth
b. Mutation for CHED1 has also been mapped to 20p11-20q11
c. Progressive
2.CHED 2
a.Autosomal recessive, central corneal edema from birth
b. Nystagmus
c. Not progressive
VIII. Summary of the Molecular Genetics of the Corneal Dystrophies
IX. The Reclassification of the Corneal Dystrophies by Affected Chromosome
X.
Implications of Molecular Genetics for the Future Management of the Corneal Dystrophies