Inferior rectus muscle thickening in patients with thyroid-associated ophthalmopathy (TAO) causes a significant increase in intraocular pressure (IOP) upon upgaze, a recent study reports. Given the ease of misdiagnosis in glaucoma, the researchers recommend that clinicians measure IOP measurement in patients with TAO in the primary position.

The study included 50 eyes of 33 patients with TAO who presented with hypotropia in the primary position. There was significant eyeball movement restriction and inferior rectus muscle thickening. A team measured IOP changes in TAO patients and control participants in the primary and upgaze positions.

The average inferior rectus thickness in the TAO and control groups was 0.71mm and 0.36mm, respectively. In the TAO group, the mean IOP was 16.8mm Hg in primary position (hypotropia), which increased by 8.9mm Hg to 25.7mm Hg in upgaze (horizontal vision). In the control group, the mean IOP in the primary position (horizontal vision) was 15.1mm Hg, which increased by 2.5mm Hg to 17.6mm Hg in upgaze.

Compared with control participants, patients with TAO who presented with inferior rectus muscle thickening had a significantly greater increase in IOP. In the patients with TAO who underwent inferior rectus muscle recession, there was a postoperative IOP reduction in the horizontal vision by 9.4mm Hg.