We have read the article entitled “Myopic maculopathy and optic disc changes in highly myopic young Asian eyes and impact on visual acuity,” by Koh and associates, with great interest. The authors investigated 593 highly myopic male individuals in order to detect the prevalence and risk factors of myopic maculopathy, and found that highly myopic eyes were significantly more likely to have optic disc tilt, peripapillary atrophy, posterior staphyloma, chorioretinal atrophy, and myopic maculopathy. Among highly myopic eyes, 8.3% had myopic maculopathy, and it was associated with older age, reduced choroidal thickness (CT), and increased axial length (AL). The authors also indicated that CT might be an additional quantifiable prognostic parameter in young myopic eyes at risk of developing pathologic myopia. We congratulate the authors for their valuable work, and would like to ask for further details.

A number of local and systemic physiological or pathologic conditions may influence CT. In the literature, diurnal variation, systemic and local disorders and the medications used for their treatment, AL, intraocular pressure (IOP), refractive error, age, sex, and a number of other factors were shown to affect CT. Although Koh and associates addressed some factors, we would like to question the authors on some important points.

CT may show a significant diurnal variation, and it was reported that its thickness could increase up to 50% in 1 hour, and 4-fold in a few days. Similarly, Kee and associates showed that the choroid can get thin by about 100 μm in 3–4 hours in young chicks.

Tan and associates measured CT in humans between 9:00 AM and 5:00 PM with 2-hour intervals, and found significant differences in CT. Tan and associates found that the mean amplitude of CT changed 33.7 ± 21.5 μm (range: 3–67 μm) during the day. The changes in CT were also correlated with changes in the systolic blood pressure (SBP). In another study Usui and associates measured subfoveal choroidal thickness (SFCT) every 3 hours over a 24-hour period in healthy subjects to study SFCT. The authors reported that the mean SFCT was thinnest (271.9 ± 103.5 μm) at 6 PM, and it was thickest (290.8 ± 110.8 μm) at 3 AM. In that study, it was shown that diurnal variation of CT might be up to 65 μm (range: 8–65 μm), and SFCT had a negative correlation with SBP.

Although the participants of the study were young, we wonder whether they had any systemic diseases or used any medications. The authors should also have mentioned exercise, sleep, and smoking statuses, as well as consumption of alcohol and caffeinated and noncaffeinated beverages before OCT measurements. We also wonder whether the body mass indexes of the patients were taken into consideration, as well as the results of their SBP measurements, since all those parameters influence CT significantly.