Dysthyroid eye disease masquerading as glaucoma.

Intraocular pressure (IOP) screening by optometrists is increasingly prevalent. Although a raised IOP usually signifies glaucoma there can be other causes, notably dysthyroid eye disease, which those screening should be aware of. The patients in the four cases presented were presumed to have glaucoma on the basis of raised IOPs, and three of them actually received medication. Because their optic nerves and visual fields showed no abnormalities this diagnosis was questioned and the cause shown to be dysthyroid eye disease. Thyroid eye disease causes raised IOP on upgaze due to a thickened inferior rectus identing the globe; however, in the primary position the IOP is normal. A misleading raised IOP can thus be found if tonometry is inadvertently done in upgaze, either because of poor patient positioning or Bell's phenomenon. Although some patients will have a past medical history of thyrotoxicosis, dysthyroid eye disease can occur in the absence of systemic or biochemical abnormalities. The important clinical signs are lid lag, lid retraction, raised IOP on upgaze and proptosis, the first three being the most common. Tonometry should thus always be done in the primary position and if raised IOPs are found without any of the other features of glaucoma, other causes particularly dysthyroid eye disease, should be considered.