To investigate the clinical effect of botulinum toxin type A (BTXA) injection on the thickness of the extraocular muscles and the improvement of strabismus in patients with restrictive strabismus of thyroid associated ophthalmopathy (TAO) under ultrasonic monitoring.

From December 2014 to December 2016, 18 patients (21 eyes) with TAO restricted strabismus were injected with BTXA under the guidance of non-electromyography. The thickness of extraocular muscles was measured before injection, 1 week, 1 month and 3 months after injection with ultrasound, and the improvement of strabismus degree was observed.

The thickness of extraocular muscles in all patients decreased after injection. The difference was statistically significant in different time before and after injection (F=26.72, P<0.01). The 11 eyes in this group were in the active stage. The thickness of the extraocular muscles was less than that before the injection, 1week, 1 month and 3 months after injection. The difference was statistically significant (t=5.31, 7.24, 11.60, all P<0.05) and 10 eyes at inactive stage. The thickness of extraocular muscle at 1 week after injection was higher than that before injection (t=-3.02, P<0.05). The thickness of extraocular muscles at 1 and 3 months after injection was not significantly different from that before injection. The average strabismus degree in 1 month and 3 months after injection was lower than that before injection in 21 eyes, and the difference was statistically significant (t=3.60, 4.05, both P<0.05). The mean strabismus at 1 weeks after injection was not significantly different from that before injection. In the 14 eyes with vertical strabismus, the degree of strabismus at 1 week, 1 month and 3 months after injection were all lower than those before injection, and the difference was statistically significant (t=2.39, 3.89, 4.87, all P<0.05). The two groups of strabismus were all improved effectively. There was no significant correlation between the thickness of the extraocular muscles and the strabismus during the active stage (r=0.048, P=0.758), There was a moderate correlation between the thickness of extraocular muscles and strabismus at rest (r=0.421, P=0.007).

Ultrasound provides a convenient monitoring method for the treatment of TAO restrictive strabismus. Injection of BTXA reduced the thickness of extraocular muscles in TAO patients with restrictive strabismus, and improved the strabismus.