Assessment of the number of lamellae in the central region of the normal human corneal stroma at the resolution of the transmission electron microscope

Abstract

Purpose: To determine the total number of lamellae within the central region of the human corneal stroma by using a continuous section through the corneal stroma and at the ultrastructural resolution of the electron microscope.

Methods: Six human eye bank corneas, from individuals aged between 42 and 82 years, were received in corneal storage medium (Optisol GS) and then processed for transmission electron microscopy with buffered 2% glutaraldehyde fixation. Thin sections were mounted on parallel bar copper grids for an uninterrupted full corneal thickness observation. A sequence of overlapping micrographs were taken at 2,600x magnification, printed at a final magnification of 3,640x, and assembled as a montage. The number of lamellae were counted across the corneal stromal strip by three observers, independently, by using a preagreed set of criteria for identifying individual lamella.

Results: The average number of lamellae per stroma was determined to be 242+/-4 (range, 234-247). In the more anterior region of the stroma, the density of the lamellae was 50% greater than in the posterior stroma (mean, 57+/-12 per 100 microm anteriorly vs. 38+/-5 per 100 microm posteriorly). Interobserver differences were modest and generally less than the intersample variance.

Conclusions: When assessed at the resolution of the transmission electron microscope, the number of stromal lamellae in the central region of the human cornea are higher (at approximately 240 per cornea) than most previous estimates reported from light microscopy studies.