Knapp procedure and modified Knapp procedure with Foster suture for the treatment of double elevator palsy

Objective To investigate the efficacy of Knapp procedure and modified Knapp procedure with Foster suture in the treatment of double elevator palsy(DEP). Methods Retrospective study. Twenty-two patients with congenital DEP were underwent Knapp procedure (n=15) and modified Knapp procedure(n=7). The clinical data were retrospectively analyzed, including the preoperative and postoperative vertical deviation in the primary position, ocular motility, and binocular vision. Results The average vertical deviation in the primary position was (34.7±8.6) prism diopters(PD) before surgery and (6.5±6.5) PD after surgery (t=30.41, P=0.00) in the group underwent Knapp procedure. The mean preoperative and postoperative deviations of the group underwent modified procedure were respectively (38.6±14.6) PD and (5.7±9.3)PD (t=15.33, P=0.00). The mean corrected vertical deviation of the latter (32.8±5.7) PD was greater than that of the former (28.1±3.6) PD(t=-2.39, P=0.03). The mean improved upgaze in the modified group (2.6±0.5) was more obvious than that in the Knapp group (1.9±0.6) (t=2.41, P=0.02). There is no significant difference in the surgical effect on downgaze between two groups (U=43.00, P=0.54). Seven patients having binocular vision with abnormal head posture (AHP) before surgery obtained binocular single vision in the primary position and reading position after operations. AHP disappeared or reduced to less than 5°. The surgical outcomes were satisfied in 72.7% patients. But the patients with ≥40 PD preoperative vertical deviation were under-corrected and needed the further operations. Conclusions Knapp procedure and modified Knapp procedure with Foster suture were the efficient procedures for treatment of DEP without restriction of ipsilateral inferior rectus. Both procedures can obviously correct the vertical deviation and improve upgaze without remarkable limitation of downgaze, which is good to obtain the binocular single vision in the primary and reading position. The modified procedure has more powerful effect on the corrected vertical deviation and improved upgaze. (Chin J Ophthalmol, 2017, 53: 903-907) Key words: Ophthalmoplegia; Strabismus; Oculomotor muscles; Suture techniques; Eye movements; Recovery of function