In addition, when using the Polscope, to measure the angle of meiotic spindle deviation from the 1PB, the oocyte has to be manually rotated, not only until both of the 1PB and the spindle can be clearly viewed in the same observation plane, but also until the spindle appears in the outermost layer of the cytoplasm. However, no matter how the 1PB and the spindle orient, just by post-processing, the angle can be precisely measured using the 3-D dataset obtained with FF-OCT. To measure the angle, 3-D geometry centers of the cytoplasm, the 1PB, and the spindle of the oocyte were calculated. Point O, A, and B in Fig. 2(d) are the corresponding 3-D geometry centers. With these three centers, the angle was quantified to be 101 deg. On the other hand, because the 1PB and the spindle were not oriented in the same XY plane as shown in Fig. 2(a), when scanning in the direction with FF-OCT, the two structures cannot appear in the same observation plane. However, by clipping the 3-D volume of the oocyte with a plane, which contains these three points, the 1PB and the spindle can also be simultaneously seen in a cross-section view, as shown in Fig. 2(d). Figures 2(e) to 2(g) show other oocytes with different angles of meiotic spindle deviation from the 1PB. The angles were measured to be 160, 108, and 70 deg, respectively. Accurate measurement of the angle in this way avoids the subjectivities of observers and is more reliable. Therefore, FF-OCT may provide new insight into the relationship between the angle and subsequent developmental competence.