Refractive Error and Ocular Parameters: Comparison of Two SD-OCT Systems

Purpose. Spectral domain optical coherence tomography (OCT) was used to examine the influence of refractive error (RE) on foveal retinal and choroidal thicknesses and scleral canal width (SCW). The performance of the Cirrus and Bioptigen spectral domain OCT instruments was compared in the same eyes. Methods. Both eyes of 40 healthy human subjects, aged 22 to 38 years, were dilated and imaged, with the Cirrus OCT, using 6-mm five-line rasters collapsed into one line, one centered on the fovea and one bisecting the optic nerve head. Seventy-two of the same eyes were imaged with the Bioptigen OCT, using 6-by 6-mm scans, one centered on the fovea and one on the optic nerve head. Subfoveal retinal and choroidal thicknesses and SCW were measured. Axial lengths (ALs) and REs were obtained using an IOLMaster and a Grand Seiko autorefractor, respectively. Results. Only right eyes were included in analyses. Spherical equivalent REs ranged from -12.18 to +8.12 diopters (mean [TSD], -3.44 [+/- 4.06] diopters), and ALs ranged from 20.56 to 29.17 mm (mean [+/- SD], 24.86 [+/- 1.91] mm). Myopia was associated with relatively thin choroids at the fovea (p < 0.05) but normal retinal thickness. Scleral canal width was significantly correlated with AL as measured with the Bioptigen OCT (p < 0.05). Retinal and choroidal thicknesses recorded with the Bioptigen OCT tended to be smaller than values obtained with the Cirrus OCT (mean difference, 5.63 and 24.76 Km, respectively), whereas the converse was true for the SCW (mean difference, 25.45 mu m). Conclusions. The finding that high myopes tend to have a thinner subfoveal choroid is consistent with previous studies. That high myopia was linked to enlarged scleral canals may help to explain the increased risk of glaucoma in myopia. Observed differences obtained with the Cirrus and Bioptigen instruments urge caution in comparing results collected with different instruments.