Purpose: To investigate whether the human corneal keratocyte density changes during aging.
Methods: Comparative data on keratocyte and endothelial cell density (ECD) were obtained from 178 normal corneas (89 persons ranging in age from 30 weeks of gestation to 90 years). Keratocyte density was quantified by using biochemical measurements of the stromal DNA/ mass content within the central 7-mm diameter zone (sDNA) (1 U equals 1 microgram DNA per milligram of dry tissue weight), whereas central ECD was assessed after alizarin red staining.
Results: In the first decade of life, there was a mean sDNA of 1.64 +/- 0.29 U, corresponding to 6.22 +/- 1.1 x 10(4) keratocytes per mm3. A direct correlation between keratocyte density and donor age was found (r = -0.49; p < 0.0001) with a physiologic decline of 0.3% per year throughout life (density = 6.30 x 10(4) keratocytes per mm3-190 x age). A similar decrease of 0.3% per year was observed in the ECD during adulthood, whereas the annual decline was 2.9% during infancy and childhood. The interindividual variation in keratocyte density was of the same magnitude as that seen in ECD. Moreover, keratocyte density was positively correlated with ECD (r = 0.23; p < 0.001); however, after correcting for age by multiple regression analysis, this correlation disappeared, indicating that keratocytes and endothelial cells form distinct cell populations.
Conclusions: The study demonstrates a linear loss of human corneal keratocytes as a function of age, a loss that parallels the well established decline in ECD.