Sir,

We greatly appreciate Squirrell et al for their kind comments and beautiful images. As they mentioned, the arrow in our figure can be read as pointing to the line of ELM.

We should apologize for the incomplete explanation and presentation of the figure. We have detected at least four lines at the outer segment of the fovea. The figure provided shows the higher-magnified image of the figure (Figure 1—type 3 in the paper).1 We have interpreted the uppermost line as ELM (dashed arrow), the second line as IS/OS (upper arrow), and the fourth line as RPE (lower arrow). The line between IS/OS and RPE may be the tips of the cone's outer segments (short arrow). As in many cases, the uppermost line (ELM) was faint and difficult to detect in some cases; we have defined the IS/OS line as the first or second detectable line that has similar intensity as the RPE line. This might be the same as the IS/OS line described earlier; namely, when three lines are present the uppermost line is the IS/OS.2 Thus, the arrow provided in Figure 1 in the article indicates an IS/OS line, but not ELM, and the measurement was performed for the IS/OS line. We should have been more careful in making the figure and we have to apologize for the figure leading to misunderstanding.

Figure 1
figure 1

A stratus OCT image of a RP patient was analysed in the paper. The uppermost line indicates ELM (dashed arrow), the second line IS/OS (upper arrow), and the fourth line RPE (lower arrow). The line between IS/OS and RPE may be the tips of the cone's outer segments (short arrow). ELM lines are sometimes faint in stratus OCT images.

Full size image