Thank you for your constructive comments.1 As you pointed out, the number of changes in choroidal thickness was not large, especially in eyes with spontaneously resolved central serous chorioretinopathy (CSC). In eyes with spontaneous resolution of CSC in our previous report, subfoveal choroidal thickness was 459.16±77.50 μm at baseline and decreased to 419.31±54.49 μm after spontaneous resolution; the difference was ∼40 μm. In eyes treated with photodynamic therapy, choroidal thickness was also reduced from 416.43±74.01 to 349.50±88.99 μm; the difference was ∼70 μm.2 As we described in the Discussion section, diurnal variation may have been an issue, especially when the difference was not large. Previous reports have described diurnal variations of 33.7 and 33.0 μm.3, 4
However, diurnal variation indicates a mean maximum–minimum difference in a day, not a casual change in a day. I admit that diurnal variation may result in bias; however, if the difference exceeds the amount of known diurnal variation, I believe that the difference would be meaningful.
I reviewed the OCT image data regarding the examination time and explored the incidence, which exceeded 3 h between examination at baseline and after resolution. For example, if a patient underwent OCT at 9:00 hours on 1 June and 11:00 hours on 15 July, the time difference was regarded as 2 h. There were no noticeable differences between the two groups (P=0.729; Table 1). Changes in choroidal thickness in each group were also compared. The Mann–Whitney U-test revealed no significant differences between the <3 h group and >3 h group in both spontaneous resolution and low-fluence PDT (P=0.174 and 0.207, respectively). Based on these results, I concluded that diurnal variation did not create substantial bias in the study, although the possibility did exist.
Based on another suggestion, we also usually adopt the eye-tracking feature of the Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) when performing successive OCT scans at each visit. I agree with your concern that even a minor change in the OCT scan may cause differences in choroidal thickness measurements.
Tan CSH, Cheong KX, Sadda SR . Change in subfoveal choroidal thickness in central serous chorioretinopathy. Eye 2013; 27 (10): 1221–1222.
Kang NH, Kim YT . Change in subfoveal choroidal thickness in central serous chorioretinopathy following spontaneous resolution and low fluence photodynamic therapy. Eye 2013; 27: 387–391.
Tan CS, Ouyang Y, Ruiz H, Sadda SR . Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci 2012; 53: 261–266.
Usui S, Ikuno Y, Akiba M, Maruko I, Sekiryu T, Nishida K et al. Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects. Invest Ophthalmol Vis Sci 2012; 53: 2300–2307.
The author declares no conflict of interest.
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Kim, Y. Reply to ‘Change in subfoveal choroidal thickness in central serous chorioretinopathy’. Eye 27, 1222 (2013). https://doi.org/10.1038/eye.2013.165