Changes in intraocular pressure during strabismus surgery

Objective: To determine whether the alterations in intraocular pressure (IOP) after cutting off a lateral rectus muscle during exotropia surgery could reflect the degree of muscle contracture. Design: Prospective study. Participants: Sixty eyes of 31 patients that had undergone lateral rectus recession surgery for correction of exotropia. Methods: IOP was measured using a Tono-pen XL before and after detaching lateral rectus muscles during the surgery. The changes in IOP were measured and their correlations with age, duration of disease, intermittency of exotropia, amount of exodeviation, laterality of the deviated eye, and tendon width of the muscle operated on were analyzed. Results: Themean baseline IOP was 16.3 (SD2.2)mmHg whenmeasured 5minutes after tracheal intubation and showed a significant decline to 13.5 (SD2.8)mmHg whenmeasured immediately before detachment of a muscle.However, the IOP decline over this period of preparation for muscle detachment was not correlated with any clinical variable tested. Themean IOP also showed a significant reduction, to 10.8 (SD2.3)mmHg, immediately after themuscles were cut off the globe. The peridetachment IOP reduction was positively correlated with constant exodeviation (p , 0.001), whereas there was no significant correlation with age, duration of exotropia, or tendon width. Conclusions: The changes in IOP seen after detaching an extraocular muscle during strabismus surgery may serve as a surrogate parameter to reflect the muscle contracture.