Sir,
We read with interest the article by Pekel et al1 comparing choroidal, foveal, and peripapillary retinal thickness between acromegaly patients and healthy adults. The authors reported that the mean subfoveal choroidal thickness (SFCT) was higher in acromegaly patients (374.4 vs 308.6 μm in the study and control groups, respectively).
It would be interesting, however, to know whether this thickening occurs to the same extent throughout the macula, or if certain regions are more severely affected. There is a potential limitation in measuring choroidal thickness at a single point subfoveally because point thickness measurements can be influenced by local changes in choroidal thickness or irregularities in the choroid–scleral border. The choroid is a complex three-dimensional structure with a highly anastomosed network of blood vessels. Significant topographic variations of choroidal and retinal thicknesses at the macula have been reported.2, 3 Some regions of the choroid may be more sensitive to endocrinological changes in acromegaly.
It may thus be useful to measure choroidal thickness at different regions of the macula, for example, at different distances from the fovea both vertically and horizontally, or by assessing mean choroidal thicknesses of pre-defined sectors using the Early Treatment Diabetic Retinopathy Study grid.
We are curious to know if the time of the optical coherence tomography scans were standardized, or if they occurred at different times of the day. Earlier studies have demonstrated significant diurnal variation of SFCT measured using spectral-domain optical coherence tomography.4 As the amplitude (difference between the maximum and minimum choroidal thickness) has been reported to be as high as 67 μm, and this amplitude is greater among patients with thicker choroids,4 the observed difference in SFCT between diseased and normal eyes in this study (mean 65.8 μm) could partly be accounted for by diurnal variation.
In summary, we congratulate the authors on their interesting findings and look forward to further studies examining the ocular effects of acromegaly at various regions of the macula. It is increasingly evident that the choroid has important roles in normal physiology and in ocular diseases, the study of which will be greatly facilitated by the new swept-source optical coherence tomography devices.5
References
Pekel G, Akin F, Ertürk MS, Acer S, Yagci R, Hıraali MC et al. Chorio-retinal thickness measurements in patients with acromegaly. Eye (Lond) 2014; 28: 1350–1354.
Tan CS, Cheong KX, Lim LW, Li KZ . Topographic variation of choroidal and retinal thicknesses at the macula in healthy adults. Br J Ophthalmol 2013; 98: 339–344.
Tan CS, Cheong KX . Macular choroidal thicknesses in healthy adults—relationship with ocular and demographic factors. Invest Ophthalmol Vis Sci 2014; 55: 6452–6458.
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: 261–266.
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 2014; 99: 354–358.
Acknowledgements
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 receives no funding.
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Cheong, K., Tan, C. Chorio-retinal thickness measurements in patients with acromegaly. Eye 29, 1111–1112 (2015). https://doi.org/10.1038/eye.2015.56
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DOI: https://doi.org/10.1038/eye.2015.56