Independent Effects of Axial Length and Intraocular Pressure on the Highly Myopic Optic Nerve Head.

PURPOSE

The purpose of this study was to investigate associations among intraocular pressure (IOP), axial length (AXL), and optic nerve head (ONH) characteristics in highly myopic eyes.

METHODS

This retrospective cross-sectional study included highly myopic eyes with a refractive error of ≤-6.0 diopters (D) or an AXL of ≥26 mm, without glaucomatous optic neuropathy. Using IOP profiles, obtained retrospectively over a 5-year period, we assessed maximum, median, and range of IOP readings. We performed cross-sectional measurements of morphometric ONH parameters on fundus photographs and optical coherence tomographic (OCT) images.

RESULTS

The study included 201 eyes (134 individuals) with a mean AXL of 27.6 ± 1.4 mm and a mean maximum IOP of 16.6 ± 3.7 millimeters of mercury (mm Hg; median = 14.9 ± 2.5 mm Hg, range = 3.14 ± 3.13 mm Hg obtained in 5.25 ± 2.76 measurements). Longer AXL was associated (multivariable analysis) with higher disc ovality (β = 0.05, P < 0.001), longer disc-fovea distance (β = 0.22, P < 0.001), shallower lamina cribrosa depth (β = -20.5, P = 0.02), and thicker ganglion cell layer and retinal nerve fiber layer in the temporal/inferotemporal sectors (all P < 0.05) with adjustments for age and gender. Higher mean maximum IOP readings were linked to deeper lamina cribrosa depth (β = 6.03, P = 0.006) and reduced disc rotation angle (β = -0.31, P = 0.04); higher mean median IOP was associated with smaller Bruch's membrane opening area (β = -0.06, P = 0.02). AXL was inversely associated with mean median IOP (β = -0.19, P = 0.02).

CONCLUSIONS

Higher IOP and longer AXL are associated with distinct structural changes of the ONH in highly myopic eyes, particularly involving the lamina cribrosa. Elevated IOP but not AXL was associated with ONH features characteristic of glaucoma.