Optic disc appearance may predict visual field progression in normal-tension glaucoma

This retrospective study found that the rate of visual field progression in patients with normal-tension glaucoma (NTG) could be linked to baseline optic disc appearance. Thus, optic disc appearance may be useful for the management of patients with NTG.

NTG can be difficult to monitor and manage. Some indication of which patients are at greater risk for steep decline in visual function, and hence require aggressive treatment, would be useful.

The authors reviewed the charts of 209 NTG patients being treated with topical antiglaucoma drugs who were followed for at least three years. The patients were classified into four groups according to optic disc appearance: focal ischemic (FI), myopic glaucomatous (MY), senile sclerotic (SS) and generalized cup enlargement (GE). NTG progression was assessed by the slope of the mean deviation (MD) obtained from the visual field results collected during follow-up.

There were no significant differences in the percentage reduction of IOP among the four groups. However, the MD slope in the GE group was significantly steeper than that in the other groups, while the MY group had the flattest slope. This indicates that patients with the GE type of optic disc have a greater likelihood of visual field progression.

Regression analyses showed that the factors most associated with the MD slope were patient age in the FI and GE groups and reduction of the IOP in the SS group. None of the factors in the MY group was significantly associated with the MD slope.

The authors note that patients in the MY group were significantly younger than those in the other groups but still had the flattest MD slope. Epidemiological studies have shown that myopia is a significant risk factor for NTG, but there are no reports that myopia is a risk factor for the progression of glaucoma. These findings suggest that the rate of progression of visual field defects in the MY group was faster in the early stage of glaucoma because the axonal damage was dependent on the disc tilt during the progression of myopia. The pathogenesis and time course of visual field progression in patients with the MY disc type may be different from that of other subtypes of disc type. Therefore, these patients need to be examined at a younger age.

The authors recommend classifying optic disc type at initial examination in all NTG patients and basing the treatment protocol on the disc type.