IOP Values Peak, Fall During Thyroid Eye Disease-Related Strabismus Surgery

Strabismus, Surgery (Photo By BSIP/UIG Via Getty Images)
Pressure rises during surgical procedure, but significantly decreases after detachment of the operated muscle, researchers explain.

Thyroid eye disease (TED) is associated with elevated intraocular pressure (IOP), and research also shows that a sizable decrease in IOP occurs immediately after patients undergo surgery for restrictive strabismus. What has not been explored until now is whether there is a pattern of pressure rise and fall during this surgery, a procedure that typically involves a fair amount of globe manipulation.

Using hand-held tonometry, investigators measured the IOP of 35 eyes of 18 patients at 6 timepoints during strabismus surgery performed at a university hospital in South Korea between March 2018 and December 2020, as reported by a prospective study published in BMC Ophthalmology. Prior to the procedure, participants’ misalignment was stable for 3 months or more. Patients received general anesthesia, followed by limbal incision and standard recession without adjustable sutures. Surgeries included the following types: bilateral or unilateral inferior rectus (IR), bilateral medial rectus (MR), or contralateral superior rectus (SR) recession.

Mean IOP 1 day preoperatively was 17.2 mm Hg OD, and 18.1 mm Hg OS. During surgery, the first value measured was 21.1±4.1 mm Hg which increased to 28.6±10.6 mm Hg upon isolation of the affected muscle (P <.001). The third reading was comparable, but significantly lessened to 15.5±5.2 mm Hg after muscle detachment (P <.001). In a fifth measurement following muscle reattachment, IOP rose to 19.1±6.8 mm Hg (P =.001), and the last reading was 18.9±4.7 mm Hg (P =.750).

Although the contour of IOP rise and fall was similar regardless of the muscle operated on, patients undergoing medial rectus recession experienced higher mean pressure compared with IR and SR at most time points. Conversely, those receiving inferior rectus treatment maintained lower IOP than MR and SR. “Surgeons should be aware of the possibility of IOP elevation during strabismus surgery in patients with TED, especially during MR recession,” the investigators report. 

Bigger increases in IOP during MR procedures may be due to the greater restriction this muscle displays which requires more force to isolate it, the researchers theorized, adding MR has a smaller “orbital space to access” compared with the fellow extraocular muscles in this analysis. Prior studies have also found IR recession prompts more early post-op IOP reduction than procedures involving the other muscles.

Participants’ age at surgery ranged from 36 to 74, two-thirds were men, and half were current or former smokers. Most patients had proptosis or eyelid dysfunction, and hypotropia was the most prevalent misalignment, with mean preoperative 31.14 prism diopters in hypotropia or 35.00 prism diopters in cases of esotropia. Hyperthyroidism affected 55.6% of participants. Three eyes of 2 patients initially recruited were excluded from the data due to surgical complication.

A limitation of this investigation includes a lack of analysis for IOP change based on surgical amount, such as the extent of hypotropia. Also, general anesthesia and the specific IOP-measuring tool used can affect readings. 


Jeong A, Kim WJ. Sequential changes in intraocular pressure during strabismus surgery in patients with thyroid eye diseaseBMC Ophthalmol. Published online March 18, 2022. doi:10.1186/s12886-022-02352-8