Lamina Cribrosa and Optic Nerve Head Geometry as a Function of Myopia in Older Normal Eyes

Purpose: Increased age and levels of myopia are potential risk factors for the development of glaucoma. However, their impact on optic nerve head (ONH) structure in normal eyes has not been fully described. We examined whether differences exist in ONH and lamina cribrosa structure with myopia in older normal eyes.

Methods: Spectral domain optical coherence tomography (SDOCT) scans centered on the ONH were acquired in one eye of 15 older normal subjects (mean = 58.1 ± 7.4 years) with high myopia (spherical equivalent [SE] ≤ -6.00 D) and 16 older normal subjects (mean = 57.5 ± 6.8 years) with emmetropia to moderate myopia (SE = plano to -6.00 D). Retinal nerve fiber layer thickness (RNFLT) was quantified from 12° circular scans. ONH features were marked in each of 48 radial B-scans (20° field) using a semi-automated MATLAB program to calculate Bruch’s Membrane Opening (BMO) area and circumference, mean anterior lamina cribrosa surface depth (ALCSD), mean minimum rim width (MRW) and mean scaled MRW.

Results: Refractive errors and axial lengths (ALs) in highly myopic eyes (mean SE = -7.18 ± 1.17 D; mean AL = 26.41 ± 0.76 mm) were statistically different from emmetropic/low myopic eyes (mean SE = -1.59 ± 1.63 D; mean AL = 24.92 ± 1.06 mm) (P<.01). While RNFLT was thinner in older eyes with high myopia (85.5 ± 7.7 μm) compared to those with emmetropia/low myopia (99.2 ± 5.0 μm; P<.01), no significant differences were measured in other ONH parameters between groups. Mean MRW was significantly thinner in highly myopic eyes with larger BMO areas (P=.04) and tended to be thinner in eyes with more posteriorly-located ALCS’s (P=.09). Conversely, no significant relationships were found between MRW and ALCSD (P=.60) or BMO area (P=.54) in older eyes with emmetropia/low myopia.

Conclusion: The tendency for mean MRW to be thinner in highly myopic eyes with more posteriorly-located ALCS’s and larger BMO areas could indicate that axons are pulled toward the BMO in eyes with a deeper lamina. This anatomical configuration may increase the biomechanical susceptibility for glaucomatous axonal damage in older, highly myopic eyes.