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Letter to the editor: choroidal thickness, age, and refractive error in healthy Korean subjects.

We read with interest the article by Kim et al., describing the variation of subfoveal choroidal thickness with age, axial length, and refractive error among patients younger than 60 years. This study contributes important insights into the normal range of choroidal thickness and the factors that influence this among Asian populations. It was interesting that the authors found no significant difference in choroidal thickness for participants older than 60 years. Earlier studies have reported varying results. Ding et al. reported a decrease of subfoveal choroidal thickness of j5.40 Km for each year of life whereas Ruiz-Medrano et al. showed the opposite: an increase in mean subfoveal choroidal thickness and horizontal choroidal thickness with age. These changes could be attributed to variations in the populations studied or differences in the methods used to measure choroidal thickness. It is also possible that subjects older than 60 years may have subclinical diseases (including undiagnosed diabetes or hypertension) that affected the choroidal vasculature and its thickness. Studies have shown that choroidal thickness varies with the presence of various clinical diseases. Besides the effect of age, other factors have also been shown to influence choroidal thickness in a particular subgroup, whereas others are not affected. For example, in a study of 150 Chinese participants, spherical equivalent has been shown to affect choroidal thickness among those with spherical equivalent less than j6.0 diopters, but not those with high myopia (j6.0 diopters or higher). We completely agree with the authors that it is important to standardize the time of optical coherence tomography scans to account for diurnal variation of choroidal thickness. Part of the variation of choroidal thickness measurements in earlier reports may potentially be attributable to normal variations in choroidal thickness, and amplitudes of up to 67Km have been reported. Although many studies have studied choroidal thickness at the subfoveal region, we feel that it is important to evaluate the variation of choroidal thickness throughout the macula, as several studies have reported considerable topographic variation of choroidal thickness at the macula. Tan et al. described the differences between choroidal thickness in various sectors of the Early Treatment Diabetic Retinopathy Study grid with the temporal and superior sector being thickest and the nasal sectors being thinnest. In addition, the region of the macula that is thickest varies with the refractive status of the eye. In summary, this study contributes useful information regarding the effects of age, refractive error, and axial length on subfoveal choroidal thickness. However, it is important to study the topographic changes of various regions of the macula with age in future studies.