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Letters to the Editor

Evaluation of choroidal thickness via enhanced depth-imaging optical coherence tomography in patients with systemic hypertension

Cheong, Kai Xiong1; Tan, Colin S1,2,

Author Information
Indian Journal of Ophthalmology: August 2015 - Volume 63 - Issue 8 - p 687
doi: 10.4103/0301-4738.169793
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Sir,

We read with interest the article by Gök et al.[1] that evaluated choroidal thickness (CT) via spectral-domain optical coherence tomography (OCT) in patients with systemic hypertension. This paper aids our understanding of how CT varies with and influences systemic and ocular diseases, the study of which is also now greatly facilitated by the new swept-source OCT devices.[2]

The authors reported that there were no significant differences in subfoveal CT between the patient and control groups, between the dipper and nondipper groups, and between those with left ventricular hypertrophy and those without.[1] When comparing CT between patient groups, it is important to be cognizant of the factors that affect CT. In this study, there were no significant differences in age or gender between the control and patient groups, and the authors took into account the potential effects of diurnal variation of CT.[3] However, CT is also known to be affected by spherical equivalent (SE) and axial length (AL) of up to 25.4 µm/D and −58.2 µm/mm, respectively.[45] Furthermore, the rates of change of CT with SE and AL vary across the macula and are greater in the central and inner subfields when compared with the outer subfields.[5] Thus, it will be interesting to know if these factors were accounted for between the various groups. This may have accounted for the absence of differences in CT.

Another limitation is that the authors measured point subfoveal CT, as opposed to mean thickness measurements. The choroid exhibits topographic variation and is a three-dimensional structure with an extensive interconnected network of blood vessels. Therefore, to better examine the possible effects of systemic hypertension on choroidal topography, the authors can consider measuring CT at the superior, inferior, temporal, and nasal regions along the vertical and horizontal OCT B-scans. An additional disadvantage of point thickness measurements is that it is influenced to a larger extent by irregularities in the choroid-scleral interface or local changes in CT, when compared with mean thickness measurements. The authors can consider measuring mean CT or choroidal volume of predefined sectors via the Early Treatment Diabetic Retinopathy Study grid.[45] This may provide a more comprehensive picture compared with a single point thickness measurement.

In summary, we congratulate the authors on their findings and look forward to future studies that examine CT in systemic hypertension.

Financial support and sponsorship

Dr. Tan receives research funding from the National Healthcare Group (Singapore) Clinician Scientist Career Scheme Grant (Code: CSCS/12005). Dr. Tan also receives travel support from Bayer (South East Asia) Pte. Ltd., Heidelberg Engineering (Heidelberg, Germany), and Novartis (Singapore). Dr. Cheong does not receive funding.

Conflicts of interest

There are no conflicts of interest.

1. Gök M, Karabas VL, Emre E, Aksar AT, Aslan MS, Ural D. Evaluation of choroidal thickness via enhanced depth-imaging optical coherence tomography in patients with systemic hypertension Indian J Ophthalmol. 2015;63:239–43
2. Tan CS, Ngo WK, Cheong KX. Comparison of choroidal thicknesses using swept source and spectral domain optical coherence tomography in diseased and normal eyes Br J Ophthalmol. 2015;99:354–8
3. 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;53:261–6
4. Tan CS, Cheong KX, Lim LW, Li KZ. Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults Br J Ophthalmol. 2014;98:339–44
5. Tan CS, Cheong KX. Macular choroidal thicknesses in healthy adults – Relationship with ocular and demographic factors Invest Ophthalmol Vis Sci. 2014;55:6452–8
© 2015 Indian Journal of Ophthalmology | Published by Wolters Kluwer – Medknow