The recent report by Rahman et al.
1 describing subfoveal choroidal thickness (SFCT) measurements was interesting to read and raised several questions that further interpretation of their data may answer. The range of thicknesses (OD 172–550 μm; OS 142–563 μm) seems surprisingly large for the age range of their study participants. Using the formula for age-adjusted SFCT measurements of Margolis and Spaide
2 (366 − 1.56 × age in years) one could expect a range on the order of 290 to 320 μm.
2 In their original paper, Margolis and Spaide do not specify the ethnicity of the patients examined but one hypothesis could be that racial differences account for such variability in the current work. Although not primarily designed to test this effect, did the authors see any trend to support or refute it? Similarly, for the outliers presented in the Bland-Altman plots, was there any suggestion of a racial predilection? Is the sclerochoroidal interface more difficult to detect in some groups compared with others?
As the choroid is a highly vascular structure, blood flow and thickness are known to vary with intraocular pressure, vascular perfusion pressure,
3 and circulating endogenous catecholamines (and by inference, presumably, anxiety state).
4 Were any of these factors controlled for?