Abstract
Purpose
To investigate the reproducibility of choroidal thickness measurements in healthy Koreans using two spectral do-main optical coherence tomography (SD-OCT) instruments: Zeiss Cirrus HD-OCT (Carl Zeiss Meditec Inc., Dublin, CA, USA) and Heidelberg Spectralis (Heidelberg Engineering, Heidelberg, Germany).
Methods
Images were obtained in 60 eyes of 30 healthy undilated volunteers without ocular pathology in a clinical setting. The choroid was imaged in all subjects using Cirrus HD 1-line raster and Spectralis enhanced depth imaging (EDI). The choroid was measured subfoveally, 1500 µm temporal, and 1500 µm nasal to the fovea. All measurements were per-formed by two independent observers. One-way analysis of variance (ANOVA), Pearson correlation, and Bland–Altman analysis were used to compare measurements.
Results
The study group consisted of 15 males and 15 females. The mean age was 50.73 ± 15.09 years (range, 24-75 years). There was no significant difference in the mean choroidal thickness (p > 0.05) between systems for any location. The choroidal thickness measurements using two instruments (Cirrus vs. Spectralis) were also strongly correlated (p < 0.001).
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Figure 1.
Optical coherence tomography scans showing cho-roidal thicknesses of the same subject on Cirrus and Spectralis. (A) An OCT image of the subject on Cirrus (Carl Zeiss Meditec Inc., Dublin, CA). Image averaging is used for cho-roidal visualization. choroidal thickness measurements was taken perpendicularly from the outer edge of the hyper-re-flective retinal pigment epithelium to the inner sclera at the fo-vea, 1500 μ m temporal to the fovea, and 1500 μ m nasal to the fovea. (B) An OCT image of subject on Spectralis. Image averaging with the aid of the eye tracking and EDI are used for choroidal visualization. Choroidal thickness measurements was taken at the fovea, 1500 μ m temporal to the fovea, and 1500 μ m nasal to the fovea (CTN: choroidal thickness meas-ured at 1.5 mm nasal to the fovea, CTF subfoveal choroidal thickness, CTT choroidal thickness measured at 1.5 mm tem-poral to the fovea).

Figure 2.
Graph showing mean choroidal thickness measure-ment in normal eyes at the fovea, 1.5 mm nasal to the fovea, and 1.5 mm temporal to the fovea.

Figure 3.
Bland-Altman plots for Cirrus vs. Spectralis. (A) Bland-Altman plot for subfoveal choroidal thickness. Mean dif-ference is 2.425 (95% CI -0.174 to 5.024). The 95% limits of agreement for choroidal thickness measurements are -17.694 to 22.544. (B) Bland-Altman plot for choroidal thickness of the na-sal fovea. Mean difference is 0.733 (95% CI -1.489 to 2.956). The 95% limits of agreement are -16.476 to 17.942. (C) Bland- Altman plot forchoroidal thickness of the temporal fovea. Mean difference is 1.292 (95% CI -1.659 to 4.242). The 95% limits of agreement for choroidal thickness measurements between Cirrus and Spectralis are -21.549 to 24.133.

Table 1.
Inter-grader comparison of choroidal thickness measurements for cirrus and spectralis
Location |
Spectralis |
Cirrus |
||
---|---|---|---|---|
Correlation coefficient | p-value | Correlation coefficient | p-value | |
CTN* | 0.945 | <0.001§ | 0.919 | <0.001§ |
CTF† | 0.977 | <0.001§ | 0.966 | <0.001§ |
CTT‡ | 0.953 | <0.001§ | 0.890 | <0.001§ |
Table 2.
Summary of previous studies on demographics and choroidal thickness measurements using various optical coherence to-mographies in normal subjects