Congenital hypoplasia or aplasia of the inferior rectus muscle is an uncommon condition. Surgical treatments such as superior rectus weakening and horizontal rectus transposition have been suggested for this condition.1 To date, correction by inferior oblique anterior transposition has been reported in only two adult patients.2,3 In this article, we present the long-term follow-up outcomes of two pediatric patients with hypoplasia of the inferior rectus muscle treated by inferior oblique anterior transposition.
A 1-year-old boy was brought to our hospital because of constant head tilt to the left and left eyelid drooping since birth. He was born full term and was otherwise healthy with no history of ocular surgery. His parents denied any family history of ocular motility disorders. On examination, he adopted a 40-degree left head tilt. We noted ptosis in the left eye and marked hypertropia with a down gaze limitation in the right eye. The remaining ocular examination was normal. We scheduled an examination under general anesthesia and possible strabismus surgery when the patient was 19 months of age. Intraoperatively, absence of the inferior rectus muscle in the right eye was observed. For correction, the right inferior oblique muscle was transposed anteriorly to the site where the inferior rectus muscle would normally insert, which was 6.5 mm posterior to the limbus. The left inferior rectus muscle was also recessed 4 mm.
One month postoperatively, the patient was orthotropic in the primary position, with his head in the straight position. Computed tomography scans of the orbits confirmed hypoplasia of the right inferior rectus muscle and showed the inferior oblique muscle in the new position (Figure 1A).
(A) Postoperative orbital computed tomography scan of case 1. Sagittal view of the right orbit shows some inferior muscle remnant (red arrow) and the inferior oblique muscle in a new position (yellow arrow). (B) Postoperative eye positions of case 1 at 8 years of age.
During the patient's last follow-up visit at 8 years of age, the alternate prism and cover test revealed 3 prism diopters (PD) of right hypertropia in the primary position. There remained a −1 down gaze limitation in the right eye, with 2 PD of esotropia in the down gaze position (Figure 1B). His best corrected visual acuity was 1.0 in both eyes. The Worth 4-dot test revealed no suppression and the Titmus test revealed a stereoacuity of 100 seconds of arc.
A 2-year-old boy was brought to our hospital for abnormal eye position noted since birth. He was born full term, had no medical issues, and had no history of ocular surgery. His parents denied any family history of ocular motility disorders. On examination, 25 PD of exotropia and 70 PD of right hypertropia were observed in the primary position, and infraduction was completely absent in the right eye in the down gaze position. Cycloplegic refraction revealed a high astigmatism of −5.00 diopters (D) in the right eye. Thus, glasses and occlusion therapy were prescribed.
The patient underwent strabismus surgery at 5 years of age. Before the surgery, there remained 18 PD of exotropia and 50 PD of right hypertropia in the primary position, and infraduction was still absent in the right eye in the down gaze position (Figure 2A). Computed tomography scanning of the orbits was completed prior to the operation and revealed relative hypoplasia of the right inferior rectus muscle (Figure 2B). During the operation, we found that there was only a sheath with the anterior ciliary vessel in the inferior aspect of the eye instead of a normal inferior rectus muscle (Figure 3A). Inferior oblique anterior transposition was performed. In addition, the bilateral lateral rectus muscles were recessed 6.5 mm and the left inferior rectus muscle was recessed 4 mm.
Preoperative (A) eye positions and (B) orbital computed tomography scans of case 2. Sagittal view of the right orbit shows some inferior muscle remnant (red arrow).
(A) Intraoperative findings of case 2. Instead of the normal inferior rectus muscle, only a sheath with the anterior ciliary vessel (arrow) was observed in the inferior aspect of the eye. (B) Postoperative eye positions of case 2.
One month postoperatively, slight right hypertropia and exotropia were still noted in the primary position (Figure 3B). Slight infraduction in the right eye could be achieved in the down gaze position.
During his last follow-up visit at 7 years of age, the patient's best corrected visual acuity was 0.9 in the right eye and 1.0 in the left eye, with astigmatism of −6.00 D in the right eye. We observed 10 PD of right hypertropia and 5 PD of esotropia in the primary and up gaze positions, and 8 PD of right hypertropia and 5 PD of esotropia in the down gaze position. The Worth 4-dot test revealed alternative suppression and the Titmus test revealed a stereoacuity of 140 seconds of arc.
Clinical symptoms and signs of congenital hypoplasia or aplasia of the inferior rectus muscle may include: hypertropia and a down gaze limitation, both greater during abduction and lesser during head tilt to the involved side; A-pattern strabismus, with greater diplopia in the down gaze position, thereby causing a chin-down position; and incyclotorsion. When these symptoms and signs are apparent, hypoplasia or aplasia of the inferior rectus muscle should be considered rather than inferior rectus palsy.4
The most commonly reported surgical procedures for hypoplasia or aplasia of the inferior rectus muscle are superior rectus weakening and horizontal rectus downward transposition.1 Superior rectus weakening can be performed through recession, tenotomy, or botulinum toxin injection. Horizontal rectus downward transposition can be performed using several techniques, including entire transposition (inverse Kappa procedure), partial (one-half or two-thirds width) transposition (modified Hummelsheim procedure), and the modified Nishida procedure, in which the inferior margins of the horizontal rectus muscles are transposed inferiorly and anchored onto the sclera, as described by Makino et al.5,6 Superior rectus weakening and horizontal rectus downward transposition can be performed in a stepwise manner7 or in combination.1,8
Inferior oblique anterior transposition converts the muscle from an elevator to a depressor and anti-elevator of the globe.9 When performed unilaterally, it can markedly depress the eye. An anatomical study has demonstrated that the ligamentous structure of the neurofibrovascular bundle of the inferior oblique muscle provides the ancillary origin for the posterior temporal fibers of the muscle when its insertion is transposed anteriorly, thus allowing the muscle to work as a depressor.10 This procedure has been performed to treat hypertropia in patients with dissociated vertical deviation and inferior oblique muscle overaction,11 as well as superior oblique muscle palsy.12–14 It has also been used in the management of iatrogenic or traumatic inferior rectus muscle absence15 and congenital hypoplasia or aplasia of the inferior rectus muscle.2,3 The two reported cases of aplasia of the inferior rectus muscle, for which inferior oblique anterior transposition was performed, involved adults aged 20 and 26 years with follow-up periods of 6 and 2 months, respectively. Both cases demonstrated considerable improvement in vertical deviation in the primary position, whereas version and duction remained unchanged.2,3 Our patients received inferior oblique anterior transposition with contralateral inferior rectus recession when they were 19 months (case 1) and 5 years (case 2) of age. An acceptable and stable eye position with moderate stereopsis development was demonstrated after 6 and 2 years of postoperative follow-up, respectively. Although the procedure did not significantly change the infraduction, it could considerably improve the vertical deviation in the primary position, thus giving younger patients the chance to develop binocularity.
The risk of anterior segment ischemia was lower with inferior oblique anterior transposition than with horizontal rectus downward transposition for hypoplasia of the inferior rectus muscle.2 In addition, inferior oblique anterior transposition provided the benefit of reserving horizontal rectus muscles for exotropia or esotropia correction. In a reported case of aplasia of the inferior rectus muscle with marked exotropia, a two-step surgery was necessary when horizontal rectus transposition was selected as the technique.8 One of our patients with hypoplasia of the inferior rectus muscle also had exotropia, and inferior oblique anterior transposition with simultaneous bilateral lateral rectus recession satisfactorily corrected both vertical and horizontal deviations.
In this report, we demonstrated that in pediatric patients with unilateral hypoplasia of the inferior rectus muscle, early diagnosis and surgical management with inferior oblique anterior transposition and contralateral inferior rectus recession could effectively improve strabismus and possibly offer favorable development of stereopsis acuity in long-term follow-up periods. Additional cases are necessary to establish the effectiveness of this procedure.
- Astle WF, Hill VE, Ells AL, Chi NT, Martinovic E. Congenital absence of the inferior rectus muscle: diagnosis and management. J AAPOS. 2003;7:339–344. doi:10.1016/S1091-8531(03)00214-3 [CrossRef]
- Almahmoudi F, Khan AO. Inferior oblique anterior transposition for the unilateral hypertropia associated with bilateral inferior rectus muscle aplasia. J AAPOS. 2014;18:301–303. doi:10.1016/j.jaapos.2014.02.005 [CrossRef]
- Xueliang F, Jia Y, Zhang X, Jia N. Congenital abnormality of bilateral inferior rectus muscle with congenital vertical torsional nystagmus with DVD: a case report. Ecronicon Ophthalmology. 2015;2:108–111.
- Muñoz M. Congenital absence of the inferior rectus muscle. Am J Ophthalmol. 1996;121:327–329. doi:10.1016/S0002-9394(14)70287-9 [CrossRef]
- Makino S, Hozawa K, Kondo R, et al. Two cases of hypoplasia of the inferior rectus muscle [article in Japanese]. Jichi Medical University Journal. 2010;33:123–128.
- Makino S, Hozawa K, Kondo R, et al. Modified muscle transposition procedure for a case of inferior rectus muscle aplasia. Case Rep Ophthalmol. 2014;6:1–6. doi:10.1159/000371508 [CrossRef]
- Ingham PN, McGovern ST, Crompton JL. Congenital absence of the inferior rectus muscle. Aust N Z J Ophthalmol. 1986;14:355–358. doi:10.1111/j.1442-9071.1986.tb00471.x [CrossRef]
- Guha S, Hurakadli PM, Shah SV, Shah K. Surgical treatment of familial absence of the inferior rectus muscle. J AAPOS. 2015;19:289–292. doi:10.1016/j.jaapos.2015.02.007 [CrossRef]
- Stager DR, Weakley DR Jr., Stager D. Anterior transposition of the inferior oblique: anatomic assessment of the neurovascular bundle. Arch Ophthalmol. 1992;110:360–362. doi:10.1001/archopht.1992.01080150058028 [CrossRef]
- Stager DR. Costenbader lecture: anatomy and surgery of the inferior oblique muscle: recent findings. J AAPOS. 2001;5:203–208. doi:10.1067/mpa.2001.116273 [CrossRef]
- Black BC. Results of anterior transposition of the inferior oblique muscle in incomitant dissociated vertical deviation. J AAPOS. 1997;1:83–87. doi:10.1016/S1091-8531(97)90003-3 [CrossRef]
- May MA, Beauchamp GR, Price RL. Recession and anterior transposition of the inferior oblique for treatment of superior oblique palsy. Graefes Arch Clin Exp Ophthalmol. 1988;226:407–409. doi:10.1007/BF02169997 [CrossRef]
- Chang YH, Ma KT, Lee JB, Han SH. Anterior transposition of inferior oblique muscle for treatment of unilateral superior oblique muscle palsy with inferior oblique muscle overaction. Yonsei Med J. 2004;45:609–614. doi:10.3349/ymj.2004.45.4.609 [CrossRef]
- Keskinbora KH. Anterior transposition of the inferior oblique muscle in the treatment of unilateral superior oblique palsy. J Pediatr Ophthalmol Strabismus. 2010;47:301–307. doi:10.3928/01913913-20091118-04 [CrossRef]
- Parvataneni M, Olitsky SE. Unilateral anterior transposition and resection of the inferior oblique muscle for the treatment of hypertropia. J Pediatr Ophthalmol Strabismus. 2005;42:163–165.