The management of DVD is challenging for strabismus surgeons. Multiple approaches have been proposed for treatment for DVD. Superior rectus recession and IOAT were most regular procedures. When DVD coexisted with IOOA, IOAT is preferred, which reduces the IOOA and restricts superior floating phenomenon of DVD simultaneously [4 ,6 ,8-9 ,12]. Full IOAT includes the posterior fibers with J deformity, which formed a neurofibrovascular bundle. The neurovascular bundle provides the inferior oblique a new functional origin and converses the inferior oblique from an elevator to a depressor. The depressor effect is likely own to a combination of active contraction of the distal inferior oblique and a mechanical restriction to elevation of the eye [8 ,13].
Satisfied clinical results of IOAT for DVD with IOOA were reported in recent years [2-6]. Symmetric DVD was always treated with symmetric surgery, whereas asymmetric DVD or IOOA were more challenging. Pineles et al [9] used asymmetric IOAT to treat 14 patients with incomitant asymmetric DVD and resulted in improvements of incomitant DVD, V-pattern and IOOA. Snir et al [8] suggested bilateral IOAT with monocular-graded inferior oblique resection for asymmetric DVD with IOOA. Bothun and Summers [4] considered unilateral IOAT was an effective treatment for unilateral or markedly asymmetric DVD in patients with a strong, contralateral fixation preference. We restricted the similar inclusion criteria with Bothun’s and achieved comparable results with previous studies.
For IOAT surgery, the optimal placement of the muscle was controversial. The standard placement was at the temporal border of the inferior rectus muscle insertion. Recently, Fard [6] suggested inferior oblique anterior nasal transposition might mechanically restrict elevation of the eye, and achieved satisfied results for DVD with IOOA. Engman et al [14] considered more anterior placement of the inferior oblique does not increase its effectiveness. Mims and Wood [15] placed the inferior oblique to a position 2 to 4 mm anterior to the lateral end of inferior rectus muscle insertion. Seawright and Gole [16] performed graded IOAT to positions located 2 mm posterior to and 2 mm anterior to the temporal position of the inferior rectus insertion according to the presence or amount of preoperative IOOA, V pattern, hypertropia, and DVD. Kratz [17] graded 1 mm posterior to and 1 mm anterior to the temporal position of the inferior rectus insertion based on the severity of DVD. We performed similar placement position as Kratz’s, but we graded for the position based on the degree of IOOA. In the monocular procedure, we achieved satisfied result by reducing the unilateral IOOA from 2.4 to 0.3.
With the generalization IOAT, some side-effects were mentioned, such as hypotropia [5-6 ,18], anti-elevation syndrome [5 ,15 ,19], and increased IOOA in the contralateral eye postoperatively [18]. Even though hypotropia and anti-elevation were also reported in the unilateral IOAT surgery, the complications were often transient or mild [4 ,10]. In our study, IOOA and DVD were significantly reduced in all patients and there were no related complications. Postoperatively, no change was found in our patients about contralateral eye DVD, IOOA, diplopia, and fixing property. It was probably related to our inclusion criteria with unilateral IOOA, significantly different primary position DVD in both eyes, and surgery on non-fixing eye. Because non-fixing eye always occupied higher position, IOAT on non-fixing eye could improve floating phenomenon of DVD, with less complications.
In conclusion, according to the retrospective study, for patients with asymmetric DVD coexist with unilateral IOOA, unilateral IOAT could be recommended.