Insidious Myopic Comitant Esotropia in a Teenager

Introduction

Acute acquired comitant esotropia (AACE) is a rare disease with a prevalence of approximately 0.3%.¹ Type III AACE, also known as Bielschowsky esotropia, is associated with uncorrected myopia of −5.00 diopters or more,² and its etiology may be related to excessive near-work activities.^1,2 It is characterized by acute onset and diplopia at distance fixation.^1,2 Comitant esotropia in myopia is characterized by diplopia initially at distance and then at near.^3,4 Different from Bielschowsky esotropia, the onset is insidious, vary grade of myopia and esotropia is slowly progressive and usually occurs in adulthood.³ To date, there is only one report relating to acquired distance esotropia associated with myopia in a study involving 11 young adults.⁴ Here, we report a rare case of what we termed “insidious myopic comitant esotropia” (IMCE) in a teenager.

Case Report

A 15-year-old patient presented with horizontal diplopia for 2 years. He noticed that he initially had double vision at distance and subsequently developed diplopia at near. His refractive status was myopia of −2.00 diopters (D) in both eyes. He wore spectacles only for distance vision. He had a history of smartphone usage of more than 6 hours per day. He denied any history of stress, trauma, or underlying disease. A photograph of when he was 6 years old showed that he was orthophoric at this age (Figure 1). On examination, his unaided visual acuity (VA) was 20/50 in both eyes and the best-corrected VA with −2.00 D was 20/20 in both eyes. A similar refractive error was found using cycloplegic refraction. Examination of the anterior and posterior segments was unremarkable. Orthoptic examination revealed esotropia of 35 prism diopters (PD) at distance and 30 PD at near (Figure 2) by the alternated prism cover test. The deviation difference was less than 5 PD in all gazes. Esotropia at near worsened with spectacles, at which point the patient also developed diplopia. Ductions and versions were full in both eyes. The Worth 4-dot test demonstrated diplopia at both distance and near. The result of the Bagolini striated glasses test showed unsuppressed esotropia. The accommodative convergence to accommodation ratio was 4:1 as determined by the lens gradient method. Computed tomography (CT) of the brain and orbits was unremarkable. The patient underwent a bilateral medial rectus recession of 5.5 mm. The distance between the medial rectus insertion site and the limbus was 5.3 mm in the right eye and 5.2 mm in the left eye. There was no complication after treatment. He was orthophoric at both distance and near with stereoacuity Timus test of 40 sec of arc (Figure 3). The Bagolini striated glasses test at 3 months post-surgery showed normal binocular single vision. The follow-up time was 8 months, and there was no recurrence of esotropia.

Figure 1 A photograph of the patient before the onset of insidious myopic comitant esotropia.

Figure 2 A photograph showing the deviation before treatment.

Figure 3 A photograph after surgical treatment.

Discussion

Myopic comitant esotropia in our case demonstrated insidious rather than acute onset in AACE. The pathogenesis of the IMCE is still unclear. Prolonged adduction of the medial rectus muscle from near-target convergence could have resulted in the shortening of the medial rectus muscle and advanced the insertion, leading to diplopia initially at distance and eventually at near.⁵ Moreover, in a study on young adults with myopic esotropia, pathological examination of the lateral rectus showed muscle atrophy, which worsened esotropia over time.⁴ Furthermore, IMCE was associated with varying grades of myopia,^3,4 and the patient already wore spectacles with normal accommodation. In IMCE, convergence abnormality plays a substantially more important role than accommodation, which can lead to the development of acquired esotropia. Type III AACE, meanwhile, the etiology of esotropia is uncorrected myopia of −5.00 diopters or more.² Abnormalities in accommodation and vergence with low fusional divergence or latent esophoria underly esotropia in AACE.^5,6

Our case showed an early age of onset, which might be related to excessive smartphone use. Excessive near-activities can accelerate the progression of esotropia, both AACE and IMCE.

The other causes of acute comitant esotropia in adults include age-related distance esotropia, divergence palsy, accommodative esotropia, decompensated esophoria and some neurological disorders. Acquired esotropia may be related to an abnormal lesion in the brain or orbits, and neuroimaging is suggested. Our case showed normal CT brain and orbit.

The patient underwent bilateral medial recession augmented by 0.5 mm relative to Parks’⁷ standard surgical formula.⁸ Intra-operation, we found that the distance from the insertion of the medial rectus to the limbus was shorter than normal (5.0 mm. right eye and 5.0 mm. left eye), which may be indicative of strengthened convergence.⁹ Eye alignment and binocular function were fully restored after surgery.

In conclusion, we demonstrated a case of insidious onset of myopic comitant esotropia in a teenager, in whom disease onset may have been accelerated by excessive smartphone usage. Augmented bilateral medial rectus recession yielded a good outcome.