Corrected Axial Length and Choroidal Thickness: A Correlation Analysis for Scientific Purposes

Purpose: Choroidal thickness (ChT) is an important measurement for evaluating eye and systemic disorders, but it is influenced by numerous elements, especially axial length (AL). It is known that the presence of a linear relationship between ChT and AL exists, but recently it has been shown that the AL measurement obtained with the current optical biometry is not very precise and needs to be corrected. This study aimed to verify if a similar correlation also persists with this corrected AL (ALc). Methods: All subjects underwent a complete eye examination, including spectral domain optical coherence tomography (OCT) with enhanced depth image (EDI) mode and AL measurement with IOLMaster. After a normality check of the data, the correlations between ChT with AL and ALc were investigated through the Pearson correlation coefficient. p values < 0.05 were considered statistically significant. Results: In total, 100 eyes of 50 healthy patients were evaluated. The mean AL was 24.36 ± 1.23 mm and mean ALc was 24.25 ± 1.22 mm. The mean nasal ChT, subfoveal ChT, and temporal ChT were, respectively, 250.57 ± 93.93 µm, 307.18 ± 101.66 µm, and 313.72 ± 88.86 µm. A significant negative linear correlation was found by comparing both AL and ALc to ChT (all r < -0.500, all p < 0.050). The negative linear correlation was stronger between nasal ChT and both AL and ALc (all r = -0.581). Conclusions: Through OCT and optical biometry, we confirmed that a statistically significant correlation persists between ALc and ChT, equal to the uncorrected AL. On these bases, in ChT studies or protocols, we recommend stratifying population according to ALc because linear correlation is still present; however, the cut-off values should be changed according to the systematic errors in optical biometry. In addition, both AL and ChT changes should be evaluated according to ALc.