Depth and age-dependent distribution of keratocytes in healthy human corneas - A study using scanning-slit confocal microscopy in vivo

Purpose: To document keratocyte distribution and changes with age in the cellular network of the human cornea in vivo. Setting: Department of Ophthalmology, University of Rostock, Rostock, Germany. Methods: Forty-nine eyes of 31 healthy subjects of various ages were examined with a modified Microphthal(R) scanning-slit confocal microscope (SSCM) (Hund) to document keratocyte distribution in the intact living cornea. Optical sections made by confocal microscopy were recorded on videotape, and the keratocyte density was determined for the total volume of the cornea and for the stromal sublayers. Results: The highest cell density was in the anterior stroma of the cornea immediately posterior to Bowman's membrane (24 320 cells/mm(3) +/- 6740 [SD]), the lowest in the central area (11 610 +/- 4290 cells/mm(3)), and an intermediate density in the posterior stroma immediately adjacent to Descemet's membrane (18 850 +/- 4610 cells/mm(3)). The differences were statistically significant (P < .005). The keratocyte density was significantly lower in the anterior and posterior regions in the group older than 50 years: Cell density at 4% depth was 20 960 8200 cells/mm(3) and at 96%, 15 520 +/- 4290 cells/mm(3) (P < .05). Conclusions: In healthy living corneas, the keratocyte density was high in the areas adjacent to Bowman's and Descemet's membranes and was lower in patients older than 50 years than in those younger than 50 years. Further studies are needed to document the rate of change with age and to better understand the role and capacity of aging keratocytes in regenerative processes following corneal diseases or surgical procedures.