Editors Selection IGR 16-2

Anatomical structures: Disc characteristics and RNFL defects

Harsha Rao

Comment by Harsha Rao on:

57392 Optic Disc Characteristics in Patients With Glaucoma and Combined Superior and Inferior Retinal Nerve Fiber Layer Defects, Choi JA; Park HY; Shin HY et al., JAMA ophthalmology, 2014; 132: 1068-1075

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Optic disc phenotype has long been a topic of interest in glaucoma management. There have been previous studies evaluating the relationship between optic disc phenotypes and glaucoma. In a recent cross-sectional study, Choi et al. compared the optic disc characteristics of glaucomatous eyes with initial single hemisphere involvement to glaucomatous eyes with initial bi-hemisphere involvement. They found that greater disc ovality on fundus photographs (defined as the ratio between the longest and shortest optic disc diameters) and larger horizontal tilt angle on optical coherence tomograph scans were significantly associated with bi-hemisphere involvement in early glaucoma. The authors discussed that the degree of optic disc tilt seemed to be an indicator of altered biomechanics of the posterior peripapillary sclera in eyes with glaucoma. They also hypothesized that eyes with glaucoma and increased optic disc tilt may be associated with the relatively symmetrical shearing forces across the superior and inferior sides of the lamina cribrosa compared with eyes with other disc phenotypes. This is an interesting new finding which has potential clinical implications. However, the relationship between optic disc phenotype and the severity of glaucoma may not be that simple. Although disc ovality was statistically significantly associated with bi-hemisphere damage, the strength of association was quite poor. The coefficient of determination of the univariate associations between bi-hemisphere damage and either the disc ovality score or the horizontal tilt angle was around 4%. The same result for the multivariate model was not provided by the authors. Nevertheless, the current study definitely provides a starting point for exploring the mechanical theory of glaucomatous damage further. Recent optical coherence tomography techniques have also opened up avenues to better evaluate the optic disc phenotype and with greater objectivity. Longitudinal studies evaluating optic disc characteristics in suspect eyes developing glaucoma and established glaucoma eyes that progress would be able to provide more robust evidence for the importance of optic disc phenotype in glaucoma.

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