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Editors Selection IGR 15-4

Clinical forms of glaucoma: A progression predictor in myopic normal tension glaucoma ?

Comment by Tae-Woo Kim on:

68923 Optic Disc Rotation as a Clue for Predicting Visual Field Progression in Myopic Normal-Tension Glaucoma, Sung MS; Kang YS; Heo H et al., Ophthalmology, 2016; 123: 1484-1493

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Although myopia is a well-known risk factor for glaucoma, the underlying mechanism how myopia is related to glaucomatous optic nerve damage remains unclear. Recently, optic disc rotation has become a focus of interest as an important morphologic feature of myopic eyes. It has been reported that the direction of optic disc rotation was a strong predictor of VF defect location in NTG eyes. Sung et al. investigated the factors associated with visual field (VF) progression in myopic normal-tension glaucoma (NTG) and determined the relationship between optic disc rotation-VF correspondence and VF progression. Optic disc rotation-VF defect correspondence was defined as eyes showing inferior rotation of the optic disc had an inferior RNFL defect and corresponding VF defect in the superior hemifield and vice versa. They found that the percentage reduction in IOP from baseline, disc hemorrhage, optic disc rotation-VF defect correspondence were important prognostic factors for patients with myopic NTG.

The most intriguing finding of this study is the negative association of optic disc rotation-VF defect correspondence with VF progression. Of the eyes with correspondence, more than 70% remained constant without VF progression during a mean follow-up period of six years. This finding suggests that the optic disc rotation has a role in developing RNFL damage and VF defects in myopic eyes, but these structural and functional changes may be static and not progressive.

Optic disc rotation has a role in developing RNFL damage and VF defects in myopic eyes, but these structural and functional changes may be static and not progressive

It remains to be elucidated why and how optic disc rotation is associated with slow VF progression. One possible hypothesis based on the recent observations is that the effect of myopia-related stress on the ONH may be alleviated with time. Some studies suggested that myopia-related tensile stress is a major or predominant insult in eyes with optic disc rotation. It is known that the optic disc changes during early childhood in myopic eyes. Such change would impose stress to the optic nerve head. At some point during life, the stress may overcome the compensatory capability, leading to RNFL damage. Thus, myopic eyes have higher chance to have glaucomatous optic neuropathy. However, since the optic disc change secondary to axial elongation is generally not a life-long process, the tensile stress associated with axial elongation or optic disc change may no longer damage the remaining optic nerve which survived against the existing tensile stress. Taken together, myopia-related tensile stress may be the predominant factor for optic nerve damage in eyes with optic disc rotation-VF defect correspondence. In such eyes, disease progression may be halted or slowed.

Determining the factors associated with faster glaucoma progression is important. At the same time, it is also important to be aware that some patients with glaucomatous optic nerve damage may not progress. Such awareness can save some patients from unnecessary aggressive treatment.

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