Korean Journal of Ophthalmology : KJO | 2021
Inferior Rectus Hypoplasia Simulating Contralateral Hypotropia: A Pediatric Case Report
Abstract
Dear Editor, This report presents a case of inferior rectus muscle hypoplasia, which was treated successfully through a recession procedure with posterior fixation of the contralateral inferior rectus. A healthy 4-month-old male infant with left eye hypotropia appeared 1 month after birth visited a strabismus clinic. The patient was delivered normally, with no sign of infection. Previous medical and family histories were insignificant. The performance in fix and follow of an object 15 cm from the face was normal in the right eye but showed moderate impairment in the left eye. The cycloplegic refraction results were +1.00 diopter sphere, -1.00 diopter cylinder ×180°, and +0.75 and -0.50 ×180° in the right and left eyes, respectively. The Krimsky test revealed 25 prism diopters (PD) of left eye hypotropia and 8 PD exophoria in primary gaze. Ductions and versions revealed one degree of supraduction deficit in the left eye, while infraduction could not be evaluated due to the patient’s inability to cooperate. Ptosis, abnormal head posture, and facial asymmetry were not present. T2-weighted coronal and sagittal imaging of the orbit and high-resolution magnetic resonance imaging of the brain stem evaluated extraocular muscles and cranial nerves, respectively. The high-resolution magnetic resonance imaging revealed hypoplasia of the inferior rectus muscle in the right eye, which was half the diameter of the left eye inferior rectus muscle (Fig. 1A1F). The other extraocular muscles appeared normal in both eyes. The bilateral oculomotor nerve appeared to be normal. The patient was diagnosed with congenital right eye inferior rectus hypoplasia. Occlusion therapy was performed on the left eye amblyopia, but the performance in fix and follow had not improved. Therefore, 5.0-mm right eye superior rectus recession and 5.0-mm left eye inferior rectus recession with posterior fixation were performed. At 2 years after surgery, the performance in fix and follow of the left eye was normal. Right eye hypertropia was <5 PD for both far and near vision. Idiopathic congenital inferior rectus hypoplasia is a rare disease with only one previously reported case in South Korea [1]. Embryologically, the inferior rectus, inferior oblique, and lateral rectus muscles originate from the inferior mesodermal complex [1]. Any problem affecting inferior mesodermal complex development can induce medical or radiologic abnormalities, such as in the present case. The bilateral oculomotor nerves were normal and symmetrical in our patient. This indicates that inferior rectus hypoplasia development has a different pathogenesis than congenital cranial disintegration disorders such as Duane retraction syndrome, congenital fibrosis syndrome, and congenital oculomotor nerve palsy [2]. We assume that inferior rectus muscle hypoplasia is caused by abnormalities of the oculomotor nerve fascicles [3]. The manifestations of congenital inferior rectus hypoplasia or aplasia are as follows: increased hypertropia during abduction, decreased hypertropia and limitation of infraduction during ipsilateral head tilting, A-pattern strabismus, diplopia exacerbation during infraduction, chindown posture, and intorsion. Inferior rectus aplasia or hypoplasia, and not inferior rectus muscle palsy, are considered when the above clinical signs are shown [4]. In children who are unable to cooperate with the strabismus examination, inferior rectus hypoplasia can be misdiagnosed as monocular elevation deficiency. If dominant Korean J Ophthalmol 2021;35(5):410-412 https://doi.org/10.3341/kjo.2021.0046