The effect of transverse ocular magnification adjustment on macular thickness profile in different refractive errors in community-based adults

Abstract

Purpose Changes in retinal thickness are common in various ocular diseases. Transverse magnification due to differing ocular biometrics, in particular axial length, affects measurement of retinal thickness in different regions. This study evaluated the effect of axial length and refractive error on measured macular thickness in two community-based cohorts of healthy young adults. Methods A total of 2160 eyes of 1247 community-based participants (18–30 years; 23.4% myopes, mean axial length = 23.6mm) were included in this analysis. Macular thickness measurements were obtained using a spectral-domain optical coherence tomography (which assumes an axial length of 24.385mm). Using a custom program, retinal thickness data were extracted at the 9 Early Treatment of Diabetic Retinopathy Study (ETDRS) regions with and without correction for transverse magnificent effects, with the corrected measurements adjusting according to the participant’s axial length. Linear mixed models were used to analyse the effect of correction and its interaction with axial length or refractive group on retinal thickness. Results The raw measures (uncorrected for axial length) underestimated the true retinal thickness at the central macula, while overestimating at most non-central macular regions. There was an axial length by correction interaction effect in all but the nasal regions (all p<0.05). For each 1mm increase in axial length, the central macular thickness is overestimated by 2.7–2.9μm while thicknesses at other regions were underestimated by 0.2–4.1μm. Based on the raw thickness measurements, myopes have thinner retinas than non-myopes at most non-central macular. However, this difference was no longer significant when the corrected data was used. Conclusion In a community-based sample, the raw measurements underestimate the retinal thickness at the central macula and overestimate the retinal thickness at non-central regions of the ETDRS grid. The effect of axial length and refractive error on retinal thickness is reduced after correcting for transverse magnification effects resulting from axial length differences.

Characterisation of the normal human ganglion cell–inner plexiform layer using widefield optical coherence tomography

“…The additional findings of significant decrease in global GCIPL thickness with increasing axial length and female sex were similar to those reported in macular OCT studies investigating demographic variables influencing the GCIPL, 17,20,21 suggesting that these trends persist in widefield investigations of the GCIPL. In particular, the association of increasing axial length with decreasing GCIPL thickness in peripheral macular locations appears consistent with the present findings, 21,50 given the greater retinal area imaged using widefield OCT. While the magnitude of this effect was reduced with adjustment of transverse magnification, 50 suggesting axial length-induced magnification effects contributed in part to these observations, the persistence of these trends with correction for axial length plus reported correlations between GCL volume adjusted for axial length and optic chiasm volume 79 may indicate axial length-dependent variations independent of magnification.…”

“…In particular, the association of increasing axial length with decreasing GCIPL thickness in peripheral macular locations appears consistent with the present findings, 21,50 given the greater retinal area imaged using widefield OCT. While the magnitude of this effect was reduced with adjustment of transverse magnification, 50 suggesting axial length-induced magnification effects contributed in part to these observations, the persistence of these trends with correction for axial length plus reported correlations between GCL volume adjusted for axial length and optic chiasm volume 79 may indicate axial length-dependent variations independent of magnification. Perhaps it is not surprising therefore that with the inclusion of more peripheral retinal locations in the widefield OCT scan, the significant association persists.…”

Macular outer nuclear layer, ellipsoid zone and outer photoreceptor segment band thickness, axial length and other determinants

“…In the OCT device used in our study (Spectralis®), the image magnification by the ocular media may at least partially be compensated for by taking into account of the keratometric readings of the individual eye. In a previous study conducted by Niyazmand et al, the raw retinal thickness measurements by the Spectralis® were underestimated for the foveal region and overestimating in extrafoveal regions 35 . For each axial length increase by one millimeter, the foveal thickness was overestimated by 2.7 μm to 2.9 μm and the retinal thickness in extrafoveal regions was underestimated by 0.2 μm to 4.1 μm.…”

Capturing the Transition From Intermediate to Neovascular AMD: Longitudinal Inner Retinal Thinning and Factors Associated With Neuronal Loss

“…A final limitation is intrinsic to OCT technology, as variations in transverse magnification primarily caused by differences in axial length may have an impact on individual retinal thickness measurements. 35 However, individual differences in retinal image magnification may be marginal in our analysis, which assessed longitudinal changes in retinal layer measurements rather than differences in these metrics between two groups.…”