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Overestimation of subfoveal choroidal thickness by measurement based on horizontally compressed optical coherence
Jae Hui Kim1, Se Woong Kang, Hyo Shin Ha
1Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, #50 Irwon-dong, Kangnam-gu, Seoul 135-710, Korea.
Purpose:
To measure the difference in subfoveal choroidal thickness between 1:1 pixel (horizontally compressed) images and 1:1 micron images in age-related macular degeneration.
Methods:
This study included 122 eyes from 122 patients diagnosed with age-related macular degeneration. Choroidal thickness was measured using enhanced-depth imaging optical coherence tomography. The measurement line was drawn as a perpendicular line between Bruch's membrane and the chorio-scleral interface. The thickness was compared between measurements based on a 1:1 pixel image and a 1:1 micron image. Eyes with a straight vertical measurement line and oblique measurement line were classified into vertical measurement group and oblique measurement group, respectively. Intra-group comparisons of subfoveal choroidal thickness measurements based on the 1:1 pixel images and the 1:1 micron images were performed for the two groups.
Results:
The mean subfoveal choroidal thicknesses measured on the 1:1 pixel images and the 1:1 micron images were 232.3 ± 106.4 μm and 228.9 ± 108.1 μm, respectively (p = 0.003). In the vertical measurement group (86 eyes), the mean subfoveal choroidal thickness was 226.3 ± 109.9 μm and 225.4 ± 112.0 μm, respectively (p = 0.423). In the oblique measurement group (36 eyes), the thickness was 246.5 ± 97.3 μm and 237.5 ± 98.9 μm, respectively (p < 0.001).
Conclusions:
Significant overestimation of the subfoveal choroidal thickness was noted when it was measured on a 1:1 pixel image. This finding suggests that the measurement of choroidal thickness should be performed based on a 1:1 micron image, especially if the measurement line is not vertical.