Thyroid disease, a risk factor for optic neuropathy mimicking normal-tension glaucoma.

The aethiology and pathogenesis of normal-tension glaucoma (NTG) is unknown but increasing evidence suggests multiple mechanisms of damage. Six out of 25 NTG patients (24%) had thyroid disease. The mean age of these patients was 66.5 +/- 9 years and of those without thyroid disease 60.7 +/- 9.6 years. The thyroid group was more hyperopic. The difference in mean intraocular pressure was not significant, but in the thyroid group the mean diurnal IOP variations were significantly smaller. The pattern VEP results indicated a correlation between optic neuropathy and prolonged latency of the P100 component in the group with thyroid disease and a correlation between optic neuropathy and lowered N80-P100 amplitudes in the group without. For one patient with hypothyroidism the delayed latency in the worse eye was normalized after thyroxine substitution. Due to overlapping the absolute values of P100 and the N80-P100 peak-peak amplitudes in pattern VEP cannot be used for differential diagnosis. These findings indicate that thyroid disease either causes optic neuropathy mimicking glaucomatous damage or is a risk factor for glaucoma.