We appreciate the comments of Drs Tan and Agrawal on our binarization method of assessing the relationship between the luminal and stromal areas of the choroid in the optical coherence tomographic (OCT) images of normal eyes and eyes after photodynamic therapy. At present, most analysis of the choroid is done on the choroidal thickness, while our method examines both the luminal and stromal areas, or the “choroidal structure.” We showed that our method had high repeatability and reproducibility, and the “choroidal vascularity index,” the proportion of luminal area to cross-sectional choroidal area, of the normal eye was approximately the same, at 65%, in 2 independent studies. A second strength in our method is that it is relatively objective and requires about 5 minutes to analyze 1 OCT image. And finally, our method uses an easily accessible software called ImageJ. Thus, our method can be used by anybody and can be used to confirm or reject our findings. Taking advantage of these features, it would be easy to compare the data of different studies of various diseases, which is most important and required for verifying the results of clinical studies.
Drs Tan and Agrawal suggested an alternative measurement, which they state as being a more stable and reliable method to monitor the changes in the choroid. They suggested calculating the proportion of luminal area to the cross-sectional choroid area instead of calculating the proportion of the luminal area to the stromal area, as we did. Unfortunately, they did not present any evidence that supported their suggestion that their method is more stable and reliable.
However, all of this may be just academic because the sum of the luminal area and stromal area is equal to the total area of the choroid. So,
Our index = luminal area/stromal area
Tan:Agrawal index = luminal area/total choroidal area
Total choroidal area = luminal area + stromal area for both
Again, we thank Drs Tan and Agrawal and wait for future studies on the normal and diseased choroid using both methods.