Percentage Choroidal Thickness: Another View on Analysis of Choroidal Thickness Using Spectral-domain Optical Coherence Tomography

Purpose: To present an analysis of the percentage choroidal thickness (PCT) and evaluate PCT profile in eyes with different axial length (AL). Methods: Axial length (AL) measurements and spectral domain optical coherence tomography examinations, including radial 9-mm scan and 4 circle scans with diameter of 3.0, 5.0, 7.0, and 9.0 mm, centered on the fovea, were performed in 35 eyes of 35 individuals (13 male, 22 female, mean age 32.2 +/- 7.1 years). Average choroidal thickness (CT) and PCT (the ratio of the average CT to the subfoveal CT) were calculated for each distance from the center of the macula and compared between three groups (AL<23.0 mm, AL 23.0-24.0 mm, and AL>24.0 mm). PCT change curves were constructed by plotting PCT values against the distance from the fovea. Results: There was no statistically significant difference in CT between eyes with different AL, except for eyes with AL>24.0 mm and AL<23.0 mm at distances of 1.5 mm (p = .01) and subfoveally (p = .003). In contrast to the linear metric, PCT showed statistically significant differences between all three AL groups at all the distances (p = .048 to p < .001) except for 3.5 mm (p = 1.0) and 4.5 mm (p = .31) between eyes with AL 23.0-24.0 mm and AL>24.0 mm and 4.5 mm between eyes with AL24.0 mm (p = .31). Conclusion: PCT change curves are significantly different between eyes with short, medium, and long axial length and may provide more representative information about the change of CT and choroidal profile in pathological conditions.