Abstract
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/axial length in older normal eyes.
Methods :
Spectral domain optical coherence tomography (SDOCT) scans (Spectralis SDOCT with Enhanced Depth Imaging) centered on the ONH were acquired in one eye of 15 older normal subjects (mean age = 58.1 ± 7.4 years) with high myopia (spherical equivalent [SE] ≤ -6.00 D) and 16 normal subjects (mean age = 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 (Inner Limiting Membrane, Bruch’s Membrane termination points, anterior lamina cribrosa surface [ALCS]) 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, mean ALCS depth (ALCSD) and mean minimum rim width (MRW). Dilated refractions were measured (RK600 autorefractor). Ocular biometry was measured (Lenstar) and used to scale SDOCT images to account for differences in retinal magnification.
Results :
Refractive errors and axial lengths (ALs) in highly myopic eyes (mean SE = -7.18 ± 1.17 D; mean AL = 26.4 ± 0.75 mm) were statistically different from low myopia eyes (mean SE = -1.59 ± 1.63 D; mean AL = 24.9 ± 1.1 mm) (P<.001). While RNFLT was thinner in older normal eyes with high myopia (mean = 85.5 ± 7.7 μm) compared to those with low myopia (mean = 99.2 ± 5.0 μm; P<.001), no significant differences were measured in BMO area, mean ALCSD and mean MRW between both groups. Mean MRW was significantly thinner in highly myopic eyes with larger BMO areas (P<.01) and tended to be thinner in eyes with more posteriorly located ALCS’s (P=.06). Conversely, no significant relationships were found between MRW and ALCSD (P=.60) or BMO area (P=.54) in older normal eyes with low myopia.
Conclusions :
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.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.