To compare the intraocular pressure (IOP) measured using Goldmann-applanation tonometry (GAT) and Tonopen® tonometry and to evaluate the factors influencing the measurement difference in patients with thyroid-associated ophthalmopathy (TAO)-related restrictive strabismus.

In 50 eyes of 50 patients who were diagnosed with TAO, IOP measurements were taken using both GAT and a Tonopen® and were subsequently compared between the devices. Factors influencing the measurement difference between the devices were determined, including the restriction of eyeball movement, eyeball deviation, exophthalmometry, central corneal thickness, refractive errors, and blood thyroid hormone levels.

In the TAO patients, the GAT-measured IOP was higher than for Tonopen® (16.1 ± 4.7 vs. 13.8 ± 4.5 mmHg, respectively, p < 0.001). As the restriction of vertical eyeball movement increased, the IOP difference between the devices also increased ( p = 0.037). The absolute IOP difference between the devices was positively correlated with restrictions in vertical eyeball movement ( p = 0.027), degree of vertical strabismus ( p = 0.021), and central corneal thickness ( p ≤ 0.031).

In patients with TAO accompanying vertical eyeball movement restriction, potential errors in IOP measurements should be considered between the different IOP-measuring devices.