### Materials and Methods

*p*-value less than 0.05 was considered statistically significant.

### Results

*p*< 0.0001, GEE), but there were no significant differences between the mean FTD of the other retinal diseases and that of the normal group. The coefficient of variation of FTD was largest in the DR group (62.2%) and smallest in the normal group (17.6%) (Table 2).

_{Stratus},

*p*= 0.13, GEE) or between FTD and Spectralis OCT-measured FT (FT

_{Spectralis},

*p*= 0.39, GEE). In the inner-retinal disease group, there was no significant correlation between FTD and FT

_{Stratus}(

*p*= 0.81, GEE), but a statistically significant positive correlation was observed between FTD and FT

_{Spectralis}(

*p*= 0.0004, GEE, FTD = 0.10 × FT

_{Spectralis}+ 25.76). In the exudative AMD group, the correlations of FTD and Modified FTD with FT measured by Stratus and Spectralis OCT were analyzed. There was a statistically significant positive correlation between FT

_{Spectralis}and FTD (

*p*< 0.0001, GEE, FTD = 0.53 × FT

_{Spectralis}- 67.61), but no significant correlation between FT

_{Stratus}and FTD (

*p*= 0.59, GEE), between FT

_{Stratus}and modified FTD (

*p*= 0.26, GEE), or between modified FT

_{Spectralis}and modified FTD (

*p*= 0.63, GEE).

_{Stratus}from FT

_{Spectralis}shown in Table 3 and Fig. 4 were statistically significant, except in the nonexudative AMD group. In Fig. 4, the prediction lines of the inner-retinal disease groups were close to that of the normal group, while the exudative AMD group showed a prediction line that deviated most from that of normal subjects and, thus, had the lowest correlation coefficient (0.47). For the exudative AMD group, an additional formula was constructed that considered CNV thickness, which resulted in a correlation coefficient for FT

_{Spectralis}(0.79) that was closer to 1.0 than that of the original formula. Fig. 2B shows the averages and SDs of the differences between the FT

_{Stratus}values calculated by the conversion formulas and the actual FT

_{Stratus}in each group. The SD was largest in the exudative AMD group (38.6 µm) and lowest in the normal subjects (11.3 µm). The SDs of the differences between predicted FT

_{Stratus}and actual FT

_{Stratus}(the right column of Table 3) were smaller than the SDs of the differences in FTDs (Table 2) in each group, except for the MH group. The SD was dramatically decreased by applying the conversion formulas in the exudative AMD group (38.6 µm from 55.0 µm). Furthermore, in the exudative AMD group, the additional conversion formula that considered CNV thicknesses was also applied, and the SD after considering CNV thicknesses (37.2 µm) was slightly smaller than that before considering CNV thicknesses (38.6 µm).

### Discussion

_{Stratus}for exudative AMD using CNV thickness (Table 3) was well-matched to our expectations of low SDs and higher correlation coefficients, and this can be interpreted to mean that the FT

_{Stratus}is equivalent to FT

_{Spectralis}less the CNV thickness (equivalent to the modified FT

_{Spectralis}).

_{Spectralis}and FTD in the exudative AMD group. However, there was no significant correlation between FT

_{Stratus}and FTD in that disease group. The higher resolution and accuracy of Spectralis OCT may be the main reasons why this has been shown in previous reports [27,28]. Another explanation is that Spectralis OCT includes CNV during the measurement of FT, and the included CNV thickness should be larger in eyes with large FT

_{Spectralis}, which leads to increased FTD with increasing FT

_{Spectralis}. This explanation is also supported by the fact that there was no correlation between FT

_{Spectralis}and modified FTD (

*p*= 0.63, GEE). Using the Modified FTD formulation, therefore, the FTD can be controlled in the accepted range even in eyes with large FT values. In Fig. 4, the prediction line for exudative AMD shows increasing discrepancy in FT

_{Stratus}values from the line of normal subjects. This could also be explained by the increasing thickness of CNV in exudative AMD eyes with increasing FT

_{Spectralis}.

_{Spectralis}but not with FT

_{Stratus}. The better accuracy of Spectralis OCT in delineating retinal borders in eyes with inner-retinal pathology, as well as outer-retinal diseases, may support the positive correlation between FTD and FT

_{Spectralis}. The use of the eye tracker when scanning the retina with Spectralis OCT results in a better localization of the fovea and a lower incidence of artifacts than when using Stratus OCT. In summary, FTD values are expected to be greater in eyes with either inner-retinal disease or exudative AMD showing large FT on Spectralis OCT than in eyes with small FT.

_{Stratus}from FT

_{Spectralis}for each retinal disease group (Fig. 4 and Table 3). The conversion formulas were different among the disease groups and statistically significant, except for eyes with nonexudative AMD. It should be noted that the SDs of the differences between actual FT

_{Stratus}and predicted FT

_{Stratus}calculated from FT

_{Spectralis}using the conversion formulas (Table 3) were smaller than the SDs of FTD (Table 2). Thus, these formulas can be useful when calculating FT

_{Stratus}from FT

_{Spectralis}according to the corresponding retinal disease, and they may be more precise than considering mean FTD alone, irrespective of the disease diagnosis.

_{Stratus}is required, and there may be less variance in FTD when using OCT devices with segmentation algorithms that are similar to those of Stratus OCT, such as Cirrus HD OCT (Carl Zeiss Meditec).