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Editors Selection IGR 18-4
Examination methods: PPA and NTG
Comment by Marcello Nicolela on:
13974 Correlation between hemifield visual field damage and corresponding parapapillary atrophy in normal-tension glaucoma, Kawano J; Tomidokoro A; Mayama C et al., American Journal of Ophthalmology, 2006; 142: 40-45
Several studies have examined the significance of peripapillary atrophy (PPA) in glaucoma, including the correlation between the amount of peripapillary atrophy and disease severity, defined by either optic disc or visual field damage. In this study, Kawano et al. (653) evaluated the differences in correlation between PPA and visual field loss in the superior and inferior hemidiscs in 109 Japanese patients with normal tension glaucoma. The rational for the study is that the inferior portion of the disc is more severely affected than the superior one, which might be particularly true in normal tension glaucoma. In this study, PPA was measured with the Heidelberg Retina Tomography (HRT), and only zone beta type of PPA was measured. The authors reported that the total PPA area was positively correlated with axial length and negatively correlated with refractive error, as expected. Surprisingly, total PPA (as well as superior and inferior PPA) were negatively correlated with age, contrary to previously published studies that showed a positive correlation between these two parameters. The most significant finding of the study is that the inferior PPA area, but not the superior one, was significantly correlated with the corresponding superior total deviation, although the correlation was relatively weak. The authors conclude that this difference in the correlation between the inferior and superior PPA and visual field loss suggests that PPA itself or the causes of PPA might explain the greater vulnerability of the inferior portion of the disc in normal tension glaucoma.
It is unfortunate that the authors did not provide a graphical display of the scatter of PPA area and total deviation for the inferior and superior areas. Moreover, since the paper only provides the correlation coefficients for the statistically significant correlations, it is difficult to really evaluate how different the correlations for the inferior and superior PPA were. An alternative explanation for the authors' findings is that significant correlations were only found for the inferior PPA because there was a greater range of inferior disc damage and consequently inferior PPA and superior visual field defect. In order to really establish if the nature of the correlation between PPA and VFD differs between superior and inferior disc regions, it would be more appropriate to match patients for the amount of visual field defect in the inferior and superior hemifields. Nevertheless, this study provides useful clinical information that PPA might be more significant in early normal tension glaucoma when it occurs inferiorly, and superior PPA might be more likely related to other factors such as refractive error in these patients.
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