Misalignment of foveal pit and foveal bulge determined by ultrahigh-resolution SD-OCT in normal eyes

Purpose The foveal bulge (FB) results from a lengthening of the outer segments of the photoreceptors which then makes the central fovea arcuate in shape. The purpose of this study was to evaluate the morphological features and locations of the FB relative to the foveal pit (FP) in a single B-scan image. Methods One hundred and forty-seven eyes of 147 healthy volunteers were studied. Horizontal and vertical B-scan optical coherence tomographic (OCT) images through the fovea were recorded by an ultrahigh-resolution spectral domain OCT (UHR-SD-OCT) instrument (Bi-μ, KOWA, Japan). The vertex of the FB and the center of the FP were identified with the ImageJ software. The distance between the FB and FP and the height of the FB were measured. Results In the horizontal images, the vertex of the FB was on the nasal side of the center of the FP in 97 eyes (66%), on the temporal side in 42 eyes (29%), and the same position in 8 eyes (5%). In the vertical images, the vertex of the FB was superior to the center of the FP in 82 eyes (55%), inferior to the center of the FP in 45 eyes (31%), and the same position in 20 eyes (14%). The mean distance (± SD) between the FB and the FP was + 16.8 ± 30.1 μm in the horizontal images and + 8.27 ± 28.0 μm in the vertical images. The mean height (± SD) of the FB was 77.0 ± 4.78 μm in the horizontal images and 77.9 ± 5.05 μm in the vertical images. The height of the FB in the horizontal images was significantly correlated with refractive error in the multiple regression analysis ( P = 0.041). Conclusions These results indicate that the vertex of the FB was not aligned with the center of the FP in the majority of the eyes of normal Japanese individuals in a single B-scan image. Analysis showed that eyes with less severe myopia had the higher height of the FB. This must be considered when interpreting the location of the vertex of the FB and the center of the FP in clinical situations.