Heterogeneity in Keratoconus: Possible Biochemical Basis

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Abstract
Total protein and collagen content in normal and keratoconus corneas were determined. The protein content (expressed as a function of dry weight) in all keratoconus corneal samples was lower than that found in normal corneas. Among the 11 keratoconus corneas examined, only 7 (group A) had the same hydroxyproline content (expressed as a function of dry weight) as normal corneas; 4 others (group B) showed significantly less. In tissue culture, 4 strains derived from keratoconus stroma (group I) produced total protein at the same rate as cells from normal controls. Four other strains (group II), had a decreased rate of protein synthesis. The amount of collagenous protein synthesized/.mu.g DNA by group I strains was similar to that found in normal cultures, whereas it was significantly reduced in group II cultures. Group I strains may represent group A corneas. Group II strains, with a reduced level of both protein and collagen synthesis, may represent group B corneas. The defect in this group appears to be decreased total synthetic activity of corneal cells. The variation in these results suggests that keratoconus is a heterogeneous disease. The heterogeneity may explain the contradictory data that exist in the literature.