Abstract
PurposeTo assess whether macular Bruch´s membrane gets lengthened in axial myopia.MethodsUsing the enhanced depth imaging mode of spectral-domain optical coherence tomography and examining a subgroup of participants of the population-based cross-sectional Beijing Eye Study, we measured the length of Bruch´s membrane (“MacBMLength”) from the fovea to the temporal edge of parapapillary gamma zone, and the distance between the fovea and the temporal optic disc border. Parapapillary gamma zone was defined as the parapapillary region without Bruch´s membrane. We additionally measured ocular biometric parameters and assessed non-ophthalmologic variables.ResultsMeasurements of MacBMLength were performed on 322 individuals. MacBMLength (mean: 3.99±0.33 mm; range: 3.17–4.93 mm) was not significantly associated with any systemic parameter or ocular biometric parameter. Gamma zone width (mean: 0.18±0.30mm; range: 0.00–2.61mm) was associated (multivariate analysis; correlation coefficient r:0.80) with longer axial length (P<0.001; standardized correlation coefficient beta: 0.60; non-standardized correlation coefficient B:0.11; 95%CI: 0.09,0.14) and with longer fovea-optic disc border distance (P<0.001; beta:0.28; B:0.19; 95%CI:0.14,0.25), but not with MacBMLength (P = 0.42). Fovea-temporal disc border distance (mean: 4.16±0.44mm; range: 3.17–5.86mm) was associated (overall correlation coefficient: 0.68) with longer axial length (P<0.001; beta: 0.36; B: 0.10; 95%CI: 0.06, 0.13), after adjusting for flatter anterior chamber depth (P = 0.003; beta:-0.14; B:-0.14; 95%CI: -0.23,-0.05) and wider parapapillary gamma zone (P<0.001; beta:0.42; B:0.62; 95%CI:0.44,0.81).ConclusionsIn contrast to parapapillary gamma zone width and fovea-disc border distance, MacBMLength was not significantly associated with axial length. Axial elongation associated increase in fovea-disc distance may predominantly occur through development or elongation of parapapillary gamma zone, while macular Bruch´s membrane may mostly be independent of axial elongation.
Highlights
Axial myopization is associated with an elongation of the globe diameters, more in the sagittal direction than in the horizontal direction or the vertical direction
Gamma zone width was associated with longer axial length (P
Fovea-temporal disc border distance was associated with longer axial length (P
Summary
Axial myopization is associated with an elongation of the globe diameters, more in the sagittal direction than in the horizontal direction or the vertical direction. If the macular region enlarges postnatally and assuming that the retinal photoreceptors do not multiply after birth or after the end of the second year of life, one may conclude that the density of the retinal photoreceptors in the macular region decreases and that the inter-photoreceptor distance subsequently increases with longer axial length. This would imply a decreased visual acuity in axially myopic eyes versus in emmetropic eyes. Since the retinal photoreceptors rest on the retinal pigment epithelium which forms Bruchs membrane as its basal membrane, the density of the foveal photoreceptors will depend on a potential lengthening of macular Bruchs membrane in axially myopic eyes
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