Histological changes of high axial myopia.

To describe pathological changes in the anatomy of highly myopic (axially elongated) eyes, enucleated globes were examined by light microscopy and ocular structures were measured histomorphometrically. These studies revealed that highly axially myopic eyes show continuous thinning of the sclera starting at or behind the equator with a maximal thinning at the posterior pole; a profound thinning of the choroid decreasing from ∼ 250 to <10 μm in extreme axial myopia, secondary macular defects in the Bruch's membrane associated with a complete loss of retinal pigment epithelium and choriocapillaris, and retinal photoreceptors; a Bruch's membrane of normal thickness in contrast to the profound thinning of the choroid and the sclera; an up to 10-fold elongation and thinning of the peripapillary scleral flange as anterior roof of the orbital cerebrospinal fluid space, and subsequently a retrobulbar extension of the cerebrospinal fluid space; an increased distance of the peripapillary arterial circle of Zinn-Haller to the optic disc border; an elongation and thinning of the lamina cribrosa with a subsequently decreased distance between the intraocular pressure compartment and the retrobulbar orbital cerebrospinal fluid pressure compartment; an increasing exposure of the peripheral posterior lamina cribrosa surface to the cerebrospinal fluid space, no longer buffered by the solid optic nerve tissue; and the development and enlargement of parapapillary gamma zone, in contrast to a myopia-independent parapapillary beta zone. These anatomical changes may be associated with high axial myopia-related complications such as an increased susceptibility of glaucomatous optic neuropathy and myopic retinopathy.