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Editors Selection IGR 21-3

Clinical Forms of Glaucoma: Chroidal thickness in myopic NTG

Comment by Tin Aung & Mani Baskaran on:

48543 Evaluation of the choroidal thickness using high-penetration optical coherence tomography with long wavelength in highly myopic normal-tension glaucoma, Usui S; Ikuno Y; Miki A et al., American Journal of Ophthalmology, 2012; 153: 10-16.e1

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In this paper, Usui et al. compared 12 highly myopic NTG eyes with 12 highly myopic normal control eyes using a prototype 1060 nm high-penetration OCT for differences in choroidal thickness (ChT) in the fovea and specific peripapillary zones. The study found that this parameter was thinner in NTG eyes and the results suggest good discriminating ability of ChT for NTG.

The pathophysiology of NTG is poorly understood and in particular, little is known about the importance of choroidal thickness and blood flow in this disease. Making a diagnosis of glaucoma in highly myopic eyes can be a challenge; particularly if IOP is normal.¹

The results of this small study were interesting for the following reasons: 1. A new type of OCT was used for the measurement of choroidal thickness; 2. Tthere was a moderate effect size (R² = 0.4) for ChT in NTG, and a new clinical biomarker was proposed to discriminate NTG in subjects with high myopia.

The findings may be of clinical relevance because it seems relatively easy to obtain ChT measurements by OCT.

In the paper, the authors speculated that the thinner ChT in NTG eyes may be associated with reduced choroidal blood flow. Another interesting suggestion from the authors was that the ChT thinning could be the effect of mechanical stretching, which may be a surrogate for lamina cribrosa changes in high myopes. The study was limited by a small sample size. Data on repeatability of ChT measurements was not provided and the authors have not specified if diurnal phasing of intraocular pressure was used in evaluation of NTG subjects. Further validation of ChT in discriminating NTG in highly myopic eyes is required in order to understand the role of this parameter in NTG and high myopia.

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