In a study on acute primary angle closure, it was demonstrated that the anterior placement of the ciliary body and ciliary body thickness were positively correlated with choroidal thickness . Knowledge of the effects of acute primary angle closure on the choroid is important because the choroid plays important roles in the eye. We would like to highlight aspects of the study design which may have bearing on the result interpretation.
The authors mentioned that the effects of diurnal variations were reduced by performing all examinations at about 1000 hours. There are studies that have used spectral-domain optical coherence tomography to demonstrate diurnal variation of choroidal thickness [2, 3]. The difference between the maximum and minimum choroidal thickness exceeded 30 µm [2, 3]. In addition, a sub-analysis of subjects with thicker choroids (defined as ≥400 µm) in one paper , demonstrated that the mean amplitude was even larger (43.1 µm) with a maximum of 59 µm. While considering diurnal variation is an important consideration, a consequence of this is that the choroidal thickness measurements would be made at different times from the initial APAC attack. This is likely to influence the correlation of choroidal thickness with the anterior placement of the ciliary body and ciliary body thickness. However, if diurnal variation is to be considered, this is likely a limitation which cannot be overcome.
Another important consideration is the topographic variation of the choroid. The choroid is a complex, three-dimensional structure comprising an anastomosing blood vessel network. Studies have reported significant variation of choroidal thicknesses at different regions of the macula using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid [4, 5]. In this study, the mean overall regional thicknesses of the choroid in the 36 sectors of the swept-source grid were calculated. However, because this is different from the choroidal thicknesses reported in earlier studies, comparison of the current study with similar studies is difficult. It would be interesting to determine if anterior placement of the ciliary body and ciliary body thickness are still positively correlated with choroidal thickness at the various ETDRS sectors. This would facilitate comparison with other studies.
In conclusion, we congratulate the authors on an interesting paper.
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Dr Cheong does any receiving funding. Dr Tan receives research funding from the National Medical Research Council Transition Award (Code: NMRC/TA/0039/2015). Dr Tan also receives conference support from Bayer (South East Asia) Pte. Ltd., Heidelberg Engineering (Heidelberg, Germany), and Novartis (Singapore).
Conflict of interest
The authors declare that they have no conflict of interest.
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Cheong, K.X., Tan, C.S. Comment on ‘Difference of uveal parameters between the acute primary angle closure eyes and the fellow eyes’. Eye 32, 1908–1916 (2018). https://doi.org/10.1038/s41433-018-0181-5