Bruch's membrane thickness in high myopia

To measure the thickness of Bruch's membrane (BM) and assess its associations with axial length.

Using a light microscope, we measured the thickness of Bruch's membrane, choroid and sclera on horizontal anterior-posterior histological sections of enucleated human globes.

The study included 54 eyes (42 with glaucomatous optic nerve damage; 23 globes with axial length ≥26.5 mm) with a mean axial length of 26.6 ± 3.3 mm (range: 21.0-34.0 mm). In the non-highly myopic eyes, BM was significantly thicker at the pars plana region (6.6 ± 1.1 μm) than at the equator (4.1 ± 1.5 μm; p < 0.001), the midpoint between equator and posterior pole (4.1 ± 1.5 μm; p < 0.001), the parapapillary region (4.5 ± 1.0 μm; p = 0.006) or the posterior pole (4.4 ± 1.7 μm; p = 0.001). At any measurement location at or behind the ora serrata, BM thickness did not differ significantly (all p ≥ 0.40) between the non-glaucomatous non-highly myopic group and the glaucomatous non-highly myopic group, or between the non-highly myopic group and the highly myopic group. BM thickness at any location was not significantly (all p > 0.45) related to axial length. The ratio of scleral thickness to BM thickness and the ratio of choroidal thickness to BM thickness significantly decreased with longer axial length for measurements taken behind the equator.

BM is physiologically thickest in the pars plana, with no major thickness differences between locations at or behind the ora serrata. In contrast to choroidal and scleral thickness, BM thickness is not significantly related to axial length. Axially elongated eyes have a normal BM thickness, despite a thinned choroid and sclera.