November 2016
Volume 57, Issue 14
Open Access
Letters to the Editor  |   November 2016
Author Response: Peripapillary Atrophy in Myopic Eyes: Comparison of Gamma to Beta Zone Ratio Between Those With and Without Glaucoma
Author Affiliations & Notes
  • Jayme R. Vianna
    Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada.
  • Marcelo T. Nicolela
    Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada.
Investigative Ophthalmology & Visual Science November 2016, Vol.57, 6032. doi:10.1167/iovs.16-20901
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      Jayme R. Vianna, Marcelo T. Nicolela; Author Response: Peripapillary Atrophy in Myopic Eyes: Comparison of Gamma to Beta Zone Ratio Between Those With and Without Glaucoma. Invest. Ophthalmol. Vis. Sci. 2016;57(14):6032. doi: 10.1167/iovs.16-20901.

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      © ARVO (1962-2015); The Authors (2016-present)

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We thank Almeida and colleagues1 for the interest in our paper2 and for the opportunity to further discuss our results. In our study, we measured the areas of gamma and beta peripapillary atrophy (PPA), which differed from previous reports that quantified PPA by width or discrete categories.3,4 Therefore, it is difficult to compare our results with some of the previous ones, and the best method for studying PPA still needs to be further evaluated. Following Almeida et al's1 suggestion, we explored using the ratio of gamma-PPA area over beta-PPA area, where gamma-PPA comprised the area external to the disc margin, with absence of both RPE and Bruch's membrane, while beta-PPA comprised the area external to the clinical disc margin, with absence of RPE and presence of Bruch's membrane. 
The median gamma/beta PPA ratio was 0.57 in the myopic controls and 0.31 in the myopic glaucoma patients (P = 0.02), confirming our original finding that gamma-PPA was larger in myopic controls and beta-PPA was larger in myopic glaucoma subjects. Although this difference was statistically significant, the distribution of the ratios on both groups overlapped widely (Fig.), and the discriminative ability of gamma/beta PPA ratio was low (area under the curve [AUC] of 0.62), similar to what we reported for either gamma or beta-PPA areas isolated (AUC of 0.59 and 0.60, respectively). Additionally, the gamma/beta PPA ratio was not significantly associated with visual field MD in myopic glaucoma patients (P = 0.87, R2 < 0.01). 
Ultimately, the bulk of evidence, including ours, suggests an association of beta-PPA, but not gamma-PPA, with these myopic individuals with glaucoma. However, it appears that this association is not strong enough to be used as a diagnostic marker of glaucoma in myopic individuals. We look forward to future studies, especially longitudinal ones exploring this topic.1552 
Figure
 
Distribution of gamma/beta PPA ratio in the myopic glaucoma (upper histogram) and myopic controls (lower histogram) groups. Proportions are relative to the number of subjects in each group. Dashed lines indicate median values.
Figure
 
Distribution of gamma/beta PPA ratio in the myopic glaucoma (upper histogram) and myopic controls (lower histogram) groups. Proportions are relative to the number of subjects in each group. Dashed lines indicate median values.
References
Almeida I, Ushida M, Lins I, Torres Dias D, Santos Prata T. Peripapillary atrophy in myopic eyes: comparison of gamma to beta zone ratio between those with and without glaucoma. Invest Ophthalmol Vis Sci. 2016; 57: 6031.
Vianna JR, Malik R, Danthurebandara VM, et al. Beta and gamma peripapillary atrophy in myopic eyes with and without glaucoma. Invest Ophthalmol Vis Sci. 2016; 57: 3103–3111.
Kim YW, Lee EJ, Kim T-W, et al. Microstructure of β-zone parapapillary atrophy and rate of retinal nerve fiber layer thinning in primary open-angle glaucoma. Ophthalmology. 2014; 121: 1341–1349.
Kim M, Kim T-W, Weinreb RN, Lee EJ. Differentiation of parapapillary atrophy using spectral-domain optical coherence tomography. Ophthalmology. 2013; 120: 1790–1797.
Figure
 
Distribution of gamma/beta PPA ratio in the myopic glaucoma (upper histogram) and myopic controls (lower histogram) groups. Proportions are relative to the number of subjects in each group. Dashed lines indicate median values.
Figure
 
Distribution of gamma/beta PPA ratio in the myopic glaucoma (upper histogram) and myopic controls (lower histogram) groups. Proportions are relative to the number of subjects in each group. Dashed lines indicate median values.
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