Retinal pigment epithelium cell density in relationship to axial length in human eyes

Purpose: To assess associations between axial length and density of retinal pigment epithelium (RPE) cells in various ocular regions. Methods: The histomorphometric investigation included histological sections of enucleated eyes of Caucasian patients. Using a light microscope, we counted the number of RPE cells on Bruch's membrane at the ora serrata, in the preequatorial region, the equatorial and retro-equatorial region, at the midpoint equator/posterior pole, and at the posterior pole. Results: The study included 65 globes with a mean axial length 25.9 +/- 3.5 mm (range: 21.0-34.0 mm). Retinal pigment epithelium (RPE) cell count in the equatorial to retro-equatorial region (p < 0.001; correlation coefficient r(2) : 0.44), in the pre-equatorial region (p < 0.001; r(2) : 0.39) and at the midpoint equator/posterior pole (p = 0.03; r(2) : 0.12) decreased with increasing axial length. Retinal pigment epithelium (RPE) cell count at the ora serrata (p = 0.49) and posterior pole (p = 0.44) was not significantly correlated with axial length. As a corollary, mean RPE cell density was higher (p < 0.001) at the posterior pole than at the midpoint equator/posterior pole or at the ora serrata region, where it was higher than in pre-equatorial region (p < 0.001) and in the equatorial to retroequatorial region (p < 0.001). Conclusions: The decrease in the RPE cell density mainly in the equatorial to retro-equatorial region in association with longer axial length suggests a region of enlargement of Bruch0s membrane in the equatorial to retro-equatorial area in association with axial elongation. The finding may be of interest to elucidate the process of emmetropization/myopization.