Keratoconus is a bilateral, non-inflammatory and progredient corneal ectasia with an incidence of approximately 1 per 2,000 in the general population. Within the second decade of life the cornea develops a conical shape, due to thinning of the corneal stroma with subsequent irregular astigmatism and myopia leading to marked impairment of vision. The most common presentation of the keratoconus is as a sporadic disorder, but it has long been recognized that a significant minority of patients exhibit a family history as an autosomal dominant mode of inheritance. Most investigators suggest complete penetrance of predisposing factors with variable phenotypic expression. In some patients heterozygous mutations in the VSX1 gene are described as the underlying gene defect. An association with Down syndrome, monosomia X (Turner syndrome), Leber's congenital amaurosis, mitral valve prolaps, collagenosis, retinitis pigmentosa and Marfan syndrome is described. The role of corneal cells in the pathogenesis of keratoconus is supported by the published reports of recurrence of keratoconus in eyes after penetrating keratoplasty due to graft repopulation by the recipient cells. Placido-based computeed videokeratographic corneal curvature mapping systems, linked with pachymetry, are useful for identifying overt and subclinical cases of keratoconus. Different indices may quantify the clinical features of keratoconus and may improve the classification. We compared videokeratometric data (Fourier series harmonic analysis and wavefront analysis) in eyes with keratoconus to answer the question of which parameters are useful for early diagnosis of keratoconus.
An expanded TGC allele with more than 50 TGC repeats in intron 2 and the described risk allele G of the polymorphism rs613872 in intron 3 of the TCF4 gene appear as an association to FECD. The chance to be affected by FECD is up to 30 times higher. With molecular genetics also donors with clinically unknown FECD may be detected.
Codon 124 of the BIGH3 gene appears as a mutation hot spot also in German families with CDL1 and CDA. Indirect mutation analysis with restriction digestion is suggested as first step investigation in families with relevant corneal dystrophies. Direct sequencing of all exons is recommended as a second step if there are no results in restriction digestion.
Irregular astigmatism and the aberration coefficient are useful parameters in detecting ectatic corneal disease using a computerized videokeratoscope. The calculation of the spherical equivalent (Fourier series harmonic analysis: no decrease of spherical equivalent in PMCD subjects) and of quadrant eccentricities are useful tools in distinguishing PMCD and keratoconus.
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