Abstract: Enhanced depth imaging spectral domain optical coherence tomography (EDI SD-OCT), based on the improvement of traditional frequency domain OCT, is a new technology used to reflect the structure of the choroid. The images are obtained by positioning the SD-OCT device close enough to the eye to present an inverted representation of the fundus, and also can quantitatively measure the choroidal thickness. So far studies about this technology are focused on the changes of the choroidal thickness. By measuring the choroidal thickness, EDI SD-OCT can not only be used to explore the pathogenesis of the diseases such as high myopia, age-related macular degeneration, polypoidal choroidal vasculopathy, etc, but also be used to differentiate age-related macular degeneration, polypoidal choroidal vasculopathy, a variety number of choroidal tumors, etc. In addition, EDI SD-OCT can be used to observe the treatment effect such as choroidal neovascularization and Vogt-Koyanagi-Harada.