The effect of strabismus muscle surgery on corneal biomechanics

Abstract

Purpose. Studying the early effect of different extraocular muscle (EOM) surgeries on corneal biomechanics. Subjects and methods. This is a prospective, nonrandomized, interventional study, in which 42 eyes of 29 candidates for EOM surgery for strabismus correction at Cairo university hospitals, aged 14-37 years, were recruited. All participants had measuring of the visual acuity, refraction (spherical equivalent (SE)), assessment of the EOM motility and muscle balance, sensory evaluation, fundus examination, and assessing the ocular biomechanics using the Ocular response analyzer (ORA, Reichert, INC., Depew, NY) noting the corneal hysteresis (CH) and corneal resistance factor (CRF) preoperatively. Same patients were reassessed using ORA 4 weeks postoperatively following a different standard EOM surgery (recti weakening/strengthening and inferior oblique weakening either (graded recession) according to the surgical indication, and ΔCH and ΔCRF were calculated, each is the preoperative - the postoperative value. Results. ΔCH and ΔCRF = -0.78 ± 1.56 and -0.72 ± 2.15, respectively, and a highly significant difference was found between each of the pre- and postoperative CH and CRF (p<0.001). 18 eyes had single EOM surgery, while 24 had multiple (2 or 3) EOM surgery; ΔCH in the single group = -1.28 ± 1.5, and ΔCH in the multiple group = 0.4 ± 1.49 (p=0.07). 23 eyes had EOM weakening surgery, while 18 had combined weakening and strengthening EOM surgery: ΔCH in the weakening group = -1.24 ± 1.77 and ΔCH in combined group = -0.26 ± 1.07 (p=0.04). A nonsignificant difference was found for ΔCRF (p=0.53). Conclusion. A different EOM surgery has an early tendency for increase of the postoperative CH specially for muscle weakening procedures (recti recession/inferior oblique muscle weakening).