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Editors Selection IGR 14-4
Clinical Examination Methods: Peripapillary atrophy
Comment by Chris Leung on:
51740 Parapapillary atrophy: histological gamma zone and delta zone, Jonas JB; Jonas SB; Jonas RA et al., PLoS ONE, 2012; 7: e47237
Parapapillary atrophy (PPA) is conventionally classified into alpha and beta zones. Jonas and colleagues re-examined the histological features of PPA in 65 enucleated human globes obtained from patients with painful absolute glaucoma (n = 55) and malignant choroidal melanoma (n = 10). One section dissecting through the central part of the optic disc was selected for measurement of gamma zone (defined as 'the distance between the end of Bruch's membrane and the outer margin of the optic nerve (covered by pia mater)'), delta zone (a central part of gamma zone in which blood vessels of at least 50'μm diameter were not detected and which had a minimal length of 300 μm') and beta zone ('the distance between the end of Bruch's membrane and the beginning of RPE'). The key finding is that beta zone was associated with glaucoma (beta zone was larger in the glaucoma group than in the non-glaucoma group) but not with axial length, whereas gamma and delta zones were not associated with glaucoma, but positively associated with axial length. The authors suggest loss of RPE cells and photoreceptors in the beta zone could be related to the optic neuropathy in glaucoma and that differentiating gamma and delta zones from the conventional 'clinical beta zone' may add diagnostic value of glaucoma.
This study provides important insights into the histology of PPA and its association with glaucoma and myopia. The description of gamma and delta zones is novel. However, the fact that some globes had co-existing glaucoma and myopia (median axial length: 27 mm; range: 21-37 mm) and that the size of the different PPA zones might not be independent of each other may have complicated the interpretation of results. The comparison of beta zone between glaucoma and non-glaucoma groups (which was based on Mann-Whitney-test) would have been more informative had axial length been adjusted in the analysis. Likewise, the significant association between axial length and gamma zone could be confounded by the presence of glaucoma. As PPA often is asymmetrically located around the optic disc, the relative proportion of the different zones of PPA likely varies with the meridian of measurement. Measuring multiple meridians of the parapapillary region in 360 degrees and analyzing the potential correlations among beta, gamma and delta zones would be relevant to address the association between PPA and glaucoma and myopia. With the advent of spectral-domain OCT, it is feasible to detect the end of photoreceptor layer, the end of Bruch's membrane/RPE, and the border tissue and quantify the different zones of PPA in multiple dimensions. OCT imaging of the optic disc and PPA in myopic patients with and without glaucoma is germane to corroborate the current findings.
