Purpose: To assess the accuracy of retinochoroidal thickness measurements obtained by ultrasonography (USG) B-Scan (over eyelids) and high-resolution immersion USG (with lids open) compared with enhanced depth imaging optical coherence tomography (EDI-OCT) in normal subjects.
Methods: Retinochoroidal thickness measurements were performed in normal subjects using USG over eyelids and high-resolution immersion USG (with lids open) using the 20-MHz probe keeping EDI-OCT as the gold standard. Mean retinochoroidal thickness at the fovea, 1.5 mm nasally and temporally were analyzed for interobserver agreement using intraclass correlation coefficient test. Paired t-test was used to compare the values obtained by the three techniques. A 10% difference was defined as clinically significant in the measurements obtained using USG compared with EDI-OCT.
Results: Thirty-two eyes of 18 healthy volunteers (15 men) with normal baseline ophthalmologic examination (spherical equivalent, -2 to +2 diopter) were enrolled. Retinochoroidal thickness measurements showed good interobserver agreement for EDI-OCT (intraclass correlation coefficient = 0.999), immersion USG (intraclass correlation coefficient = 0.983), and USG over eyelids (intraclass correlation coefficient = 0.97). Mean retinochoroidal thickness using the above 3 techniques measured 631.77 ± 98.48, 617.17 ± 95.22, and 953 ± 151.28 μm, respectively. Immersion USG measurements were not significantly different from the gold standard, that is, EDI-OCT. However, over eyelids USG provided significantly higher values (P < 0.001) when compared with EDI-OCT and immersion USG.
Conclusion: Ultrasonography over eyelids overestimates the retinochoroidal thickness. Immersion USG provides values comparable with EDI-OCT and high-quality imaging where EDI-OCT cannot be performed.