From the National Healthcare Group Eye Institute, Singapore (MCC, LWL, KXC, CSHT); Fundus Image Reading Center, National Healthcare Group Eye Institute, Singapore (CSHT); and Doheny Eye Institute, University of Southern California, Los Angeles, California (SRS, CSHT).
Supported in part by the Beckman Institute for Macular Research and Research to Prevent Blindness Physician Scientist Award (SRS) and the National Healthcare Group Clinician Scientist Career Scheme (CSHT).
Dr. Sadda is a co-inventor of Doheny Eye Institute intellectual property related to optical coherence tomography that has been licensed by Topcon Medical Systems, is a member of the scientific advisory board for Heidelberg Engineering, and receives research support from Carl Zeiss Meditec and Optovue. Dr. Tan receives conference support from Bayer, Heidelberg Engineering, and Novartis. The remaining authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Colin S.H. Tan, National Healthcare Group Eye Institute, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433; (+65) 63577726; fax: (+65) 63577718; email:
To the Editor:
We read with interest the article by Toyokawa et al1 describing the differences between morning and evening choroidal thickness measurements in Japanese subjects, which the authors concluded could be attributed to diurnal variation. This study, however, does not provide strong evidence for the pattern of diurnal variation, because measurements at only two time points do not provide compelling evidence of a specific trend.
We would like to highlight three other studies in healthy subjects that provide additional evidence to support the presence and pattern of diurnal variation in choroidal thickness. These studies measured choroidal thickness over at least five time points during a single day, allowing a more comprehensive analysis of the trend and pattern of diurnal variation.2
In a study of 12 healthy individuals, Tan et al3 performed sequential spectral-domain optical coherence tomography (SD-OCT) scans using the Spetralis OCT (Heidelberg Engineering, Heidelberg, Germany). The authors found significant diurnal variation in subfoveal choroidal thickness, with a mean amplitude (difference between the thickest and thinnest values) of 33.7 ± 21.5 μm, despite virtually no change in the neurosensory retinal thickness measured at the same time. This is greater than the mean of 20.3 μm reported by Toyokawa et al (the calculated difference between the morning and evening foveal choroidal thickness). One wonders whether, in the patients studied by Toyokawa et al, there may have been other time points when the choroidal thickness may have been thicker or thinner than their reported values, and whether this would have affected the amplitude of choroidal thickness variation. Tan et al also demonstrated a decreasing trend of choroidal thickness progressively from 9 a.m. to 5 p.m., consistent over 2 separate days, in contrast to the apparent increase between morning and evening measurements reported by Toyokawa et al.
Similarly, a study conducted in Japanese patients by Usui et al,4 which was performed over a 24-hour period, reported the same decreasing trend in choroidal thickness from 9 a.m. to 6 p.m., with the thinnest measurements occurring at 6 p.m. Furthermore, the reported amplitude was 33.0 ± 14.3 μm, consistent with that reported by Tan et al. Chakraborty et al5 used an optical biometer instead of OCT to measure choroidal thickness and also reported a significant diurnal variation in choroidal thickness, with a mean change of 29 ± 16 μm, but reported a differing pattern of diurnal variation between the 2 days.
In summary, we agree with Toyokawa et al that there appears to be significant diurnal variation in choroidal thickness in normal individuals, although the exact pattern of diurnal variation, and whether this is consistent in all individuals, remains uncertain. Therefore, when assessing choroidal thickness in clinical practice and trials, it is important to take into account the time of measurements.
- Toyokawa N, Kimura H, Fukomoto A, Kuroda S. Difference in morning and evening choroidal thickness in Japanese subjects with no chorioretinal disease. Ophthalmic Surg Lasers Imaging. 2012;43(2):109–114. doi:10.3928/15428877-20120102-06 [CrossRef].
- Tan CSH, Ngo WK, Chew MC, et al. Diurnal variation of retinal thickness measured by optical coherence tomography in normal adults. Invest Ophthalmol Vis Sci. 2012;53(3):1639–1639. doi:10.1167/iovs.12-9566 [CrossRef]
- Tan CS, Ouyang Y, Ruiz H, Sadda SR. Diurnal variation of choroidal thickness in normal, healthy subjects measured by spectral domain optical coherence tomography. Invest Ophthalmol Vis Sci. 2012;53(1):261–266. doi:10.1167/iovs.11-8782 [CrossRef]
- Usui S, Ikuno Y, Akiba M, et al. Circadian changes in subfoveal choroidal thickness and the relationship with circulatory factors in healthy subjects. Invest Ophthalmol Vis Sci. 2012;53(4):2300–2307. doi:10.1167/iovs.11-8383 [CrossRef]
- Chakraborty R, Read S, Collins M. Diurnal variations in axial length, choroidal thickness, intraocular pressure, and ocular biometrics. Invest Ophthalmol Vis Sci. 2011;52(8):5121–5129. doi:10.1167/iovs.11-7364 [CrossRef]