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Nancy J. Coletta; Retinal Thickness In Myopia After Adjustment For Axial Length Variation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3209.
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© ARVO (1962-2015); The Authors (2016-present)
Studies using optical coherence tomography (OCT) to investigate retinal thickness generally indicate that the retina is thinner in the perifoveal region and thicker in the central foveal region in myopic eyes than in emmetropic eyes. A potential factor in interpreting OCT data gathered from myopic eyes is that the transverse magnification of an OCT varies with the eye’s axial length. Lateral retinal dimensions are affected by OCT magnification (Johnson et al., ARVO, 2009). The purpose of this study was to explore whether magnification adjustments would alter the pattern of retinal thickness results in the macular region.
Measurements were made on one eye of 50 subjects; spherical equivalent refractive error ranged from +0.50 D to -12.00 D and axial lengths (AL) ranged from 21.9 mm to 29.2 mm. Retinal thickness was measured with an Optovue RTVue spectral domain OCT, using the MM6 scan pattern that consists of twelve 6-mm B-scans that rotate through the fovea. Retinal thickness was analyzed for the central 1 mm, parafovea (1-3 mm diameter ring) and perifovea (3-6 mm diameter ring). Comparisons of magnification adjustment were made for two sets of data: 1) unadjusted RTVue data were compared to RTVue values adjusted for the eye’s AL using an Optovue software upgrade; and 2) retinal thickness values calculated from the raw B-scan data were compared to adjusted B-scan data in which the transverse range in each of the twelve B-scans was shifted by an artificial eye calibration of the OCT.
The unadjusted RTVue retinal thickness significantly decreased with increasing myopia and axial length in both the parafovea (p<0.05) and perifovea (p<0.001), while the central 1 mm thickness increased significantly with myopia (p=0.02) but not with axial length (p>0.05). The difference in retinal thickness with vs. without magnification adjustment was plotted as a function of AL. Both the Optovue software and artificial eye adjustments reduced thickness in the fovea and increased thickness in the perifovea compared to their respective unadjusted data. The Optovue and artificial eye adjustments per mm AL were 0.32 and 0.39 micron in the fovea and 0.61 and 0.70 micron in the perifovea, respectively. However the adjusted data from both the Optovue software and the artificial eye did not change the overall pattern of results from their respective unadjusted data.
Adjustment for variation in axial length did not alter the pattern of retinal thickness results in the macular region in this group of eyes. Adjustment provided by an artificial eye calibration was similar to that provided by an upgrade to the Optovue RTVue software.
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