corneal shape

Keratoconus 4

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a ‘scissoring’ pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  Mutations at the 2p24 locus on chromosome 2 seem to cause KTCN4 based on genome-wide linkage analysis in families from multiple out-bred populations.  The pattern of inheritance is autosomal dominant.

Other forms of hereditary keratoconus caused by different mutations are:  Mutations in VSX1 (20p11.2) cause KTCN1, KTCN2 (608932) is linked to a mutation on chromosome 16 (16q22.3-q23.1), and KTCN3 (608586) results from a mutation on chromosome 3 (3p14-q13).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Keratoconus 3

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a 'scissoring' pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  KTCN3 seems to be caused by a mutation located at 3p14-q13 as determined from linkage studies in a 2 generation Italian family.  It is inherited in an autosomal dominant pattern.

Other forms of hereditary keratoconus caused by different mutations are:  KTCN1 (148300) caused by mutations in the VSX1 gene at 20p11.2), KTCN2 (608932) from a mutation on chromosome 16 (16q22.3-q23.1), and KTCN4 (609271) caused by a mutation on chromosome 2 (2p24).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Keratoconus 2

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a 'scissoring' pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  KTCN2 seems to be caused by a mutation located at 16q22.3-q23.1 as determined from linkage studies in 20 Finnish families.  It is inherited in an autosomal dominant pattern.

Other forms of hereditary keratoconus caused by different mutations are:  KTCN1 (148300) caused by a mutation in the VSX1 gene (20p11.2), KTCN3 (608586) from a mutation on chromosome 3 (3p14-q13), and KTCN4 (609271) caused by a mutation on chromosome 2 (2p24).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Keratoconus 1

Clinical Characteristics
Ocular Features: 

The cornea progressively thins mostly in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy may show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a 'scissoring' pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively often thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse.

Genetics

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and other chromosomal disorders. It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years. Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder. Only keratoconus associated with single gene mutations are considered here.

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  Mutations in the VSX1 homeobox gene (20p11.2) have been found in what is called KTCN1 keratoconus (the same gene is mutant in posterior polymorphous corneal dystrophy 1 [122000]), inherited as an autosomal dominant trait.

Other forms of hereditary keratoconus caused by different mutations are:  KTCN2 (608932) linked to a mutation on chromosome 16 (16q22.3-q23.1), KTCN3 (608586) by a mutation on chromosome 3 (3p14-q13), KTCN4 (609271) caused by a mutation on chromosome 2 (2p24), KTCN5 (614622) mapped to 5q14.1-q21.3, KTCN6 (614623) mapped to 9q34, KTCN7 (614629) mapped to 13q32, KTCN8 (614628) mapped to 14q24, and KTCN9 (617928) associated with a mutation in the TUBA3D gene located at 2q21.1.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

VSX1: a gene for posterior polymorphous dystrophy and keratoconus

Heon E, Greenberg A, Kopp KK, Rootman D, Vincent AL, Billingsley G, Priston M, Dorval KM, Chow RL, McInnes RR, Heathcote G, Westall C, Sutphin JE, Semina E, Bremner R, Stone EM. VSX1: a gene for posterior polymorphous dystrophy and keratoconus. Hum Mol Genet. 2002 May 1;11(9):1029-36.

PubMed ID: 
11978762
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