Esotropia is a condition in which one eye deviates inward (toward the nose) while the other eye fixates on a target. It is classified by onset age, presence of accommodation, variability of the deviation angle, and magnitude of the deviation.
Esotropia with onset within 6 months of age is classified as infantile esotropia (also called congenital esotropia). Among acquired esotropia after 6 months, accommodative esotropia involving accommodation is most common, followed by acute acquired comitant esotropia (AACE), intermittent myopic comitant esotropia (IMCE), cyclic esotropia, and secondary esotropia. It accounts for about one-third of all strabismus patients, with a prevalence estimated at 1–2% of the population.
Infantile esotropia
Onset: Within the first 6 months of life. Large angle ≥30 PD.
Complications: DVD 46–90%, IOOA 33–78%, LN 30–50%.
Treatment: Surgery (bilateral medial rectus recession) is standard. Very early surgery (≤8 months) is most favorable for stereopsis.
Accommodative esotropia
Onset: Most common subtype of acquired esotropia. Often at 2–3 years of age. Main cause is hyperopia ≥+2 D.
3 types: Refractive (orthophoric with glasses), non-refractive (high AC/A ratio), partially accommodative (residual deviation with glasses).
Treatment: Full correction glasses are first-line. Only partially accommodative type is surgical indication.
Infantile esotropia is characterized by onset within 6 months of age and large angle ≥30 PD. Accommodative esotropia is evaluated by wearing full hyperopic correction glasses for at least 3 months. In refractive accommodative esotropia, the deviation decreases by ≥10 PD and residual deviation is <10 PD. Even in infants under 1 year, if hyperopia >+2 D, trial of glasses can aid differentiation. Note that accommodative esotropia can also occur before 1 year of age, and cycloplegic refraction and glasses trial are essential for differentiation from infantile esotropia.
Large-angle esotropia is the main finding, and several associated findings frequently coexist.
Main Findings in Infantile Esotropia
Large-Angle Deviation: Esotropia of 30 prism diopters or more. The angle of strabismus rarely fluctuates but may increase.
Cross Fixation: The right eye fixates in the left visual field and the left eye in the right visual field. This may appear as abduction limitation.
Amblyopia: Occurs in about 40–50% of cases. Determined by fixation preference. If there is no alternating fixation and a preference exists, the risk of amblyopia is high.
Associated Findings in Infantile Esotropia
Dissociated vertical deviation (DVD): Complicated in 46–90% of cases. The non-fixating eye elevates during occlusion. Usually appears after 1–2 years of age.
Inferior oblique overaction (IOOA): Complicated in 33–78% of cases. Observed as elevation during adduction.
Latent nystagmus (LN): Complicated in 30–50% of cases. Horizontal jerk nystagmus induced by monocular occlusion. The fast phase beats toward the non-occluded eye.
OKN asymmetry: Asymmetry where pursuit in the ear-to-nose direction is sustained and dominant.
AACE cases are characterized by acute-onset diplopia and esotropia, and up to 10% have underlying intracranial disease 2). In IMCE cases, shortening of the distance between the medial rectus insertion and the corneal limbus (5.2–5.3 mm) has been confirmed 6).
Excessive near work using a smartphone for 6 hours or more per day has been reported to be associated with IMCE (Intermittent Myopic Consecutive Esotropia) and AACE (Acute Acquired Comitant Esotropia)2, 6). It has been hypothesized that excessive near fixation causes shortening of the medial rectus muscle and anterior displacement of its insertion.
Perform a complete ophthalmic examination (visual acuity, binocular vision, stereopsis, eye movements, angle of strabismus, cycloplegic refraction).
For esotropia, cycloplegia with atropine sulfate eye drops is the first choice (0.5% 2-3 times daily for 5-7 days). It is excellent for detecting the maximum hyperopic refractive error. A mixture of cyclopentolate 1% and phenylephrine 2.5% may be used as an alternative. After full correction under cycloplegia, the eye position is measured to determine the amount of surgery.
| Test | Method and evaluation |
|---|---|
| Hirschberg test | Estimation by corneal reflex: pupil margin = 15°, iris = 30°, corneal limbus = 45° |
| Cover test | Performed at distance (5 m) and near (33 cm). Presence of fixation switch → amblyopia risk assessment |
| Alternate prism cover test (APCT) | Quantifies deviation in prism diopters at near and distance |
| Bruckner test (red reflex) | Suitable for infants. Also useful for detecting anisometropia and cataract |
A difference in strabismus angle between distance and near ≥10 PD suggests a high AC/A ratio.
| Measurement method | Method | Normal value |
|---|---|---|
| Gradient method | Change in strabismus angle after +3D addition ÷ 3 | 4±2 PD/D |
| Heterophoria method | Distance-near phoria difference + interpupillary distance | 4±2 PD/D |
For the diagnosis of accommodative esotropia, it is essential to evaluate after wearing fully corrective glasses for at least 3 months.
| Disease | Key differentiating points |
|---|---|
| Pseudoesotropia | Epicanthal folds, flat nasal bridge. No deviation on cover test. Pinching the nasal bridge reveals it is not true strabismus. |
| Abducens nerve palsy | Abduction limitation (inability to abduct with doll’s eye phenomenon) |
| Duane syndrome (type I) | Narrowing of palpebral fissure and globe retraction on adduction |
| Möbius syndrome | Combined VI and VII nerve palsy |
| Congenital fibrosis of extraocular muscles | Check for abduction limitation using doll’s eye phenomenon |
| Ciancia syndrome | Large angle >60°, abduction limitation, fixation in adduction, ipsilateral face turn |
| Nystagmus blockage syndrome | Jerk nystagmus appears on abduction. ENG shows decelerating slow-phase waveform |
In infantile esotropia, the doll’s eye phenomenon using the oculocephalic reflex is used to confirm the absence of abduction limitation, differentiating it from abducens nerve palsy and Duane syndrome.
When AACE is suspected: MRI is mandatory. Up to 10% have underlying intracranial disease (most commonly posterior fossa lesions)2).
Amblyopia treatment: Amblyopia is present in approximately 40–50% of cases. Occlusion of the sound eye is the mainstay of treatment. If eccentric fixation amblyopia or abnormal retinal correspondence is suspected, amblyopia treatment should precede surgery.
Spectacle correction: If hyperopia of +2 D or more is present, the accommodative component should be evaluated with full correction spectacles. For hyperopia of +3 D or more, measure the ocular deviation after full correction under cycloplegia to determine the surgical dose. Since accommodative esotropia develops postoperatively in about 60% of cases, ongoing refractive management is necessary.
Surgical treatment:
The basic surgical procedure is bilateral medial rectus muscle recession. For large angles, lateral rectus muscle resection is added (three-muscle surgery) 1). Esotropia of 40 PD or more does not resolve spontaneously, so surgical indication should be determined promptly. In the PEDIG study, among infants confirmed to have 40 PD or more at 2–4 months of age, spontaneous resolution occurred in 0/45 cases and 0/21 cases 1).
Guidelines for surgical dosage (esotropia angle and recession amount):
| Esotropia angle (Δ) | Recession amount from muscle insertion (mm) | Recession amount from limbus (mm) |
|---|---|---|
| 15 | 3.0 | — |
| 25 | 4.0 | 8.5 |
| 35 | 5.0 | 9.5 |
| 45 | 6.0 | 10.5 |
| 55+ | 7.0 | 11.5 |
Maximum recession by age (from corneal limbus): <6 months → 10.0 mm, <1 year → 10.5 mm, <24 months → 11.0 mm.
Timing of surgery and binocular vision outcomes:
| Timing of surgery | Near fusion | Distance fusion | Stereopsis (+) |
|---|---|---|---|
| Very early (≤8 months) | 93.8% | 93.8% | 75.0% |
| Early (9–24 months) | 81.0% | 57.0% | 19.1% |
| Late (>24 months) | 38.9% | 27.8% | 11.1% |
p<0.001 (ultra-early vs late). Birch & Stager (2000) reported 100% stereopsis with surgery before 6 months, and 8% with surgery after 18 months.
Postoperative alignment goal: The minimum requirement for ARC to develop is to achieve microtropia within 8Δ or monofixation syndrome within 10Δ. Residual deviation ≥8Δ after surgery → use of membrane prism. Manifestation of DVD or oblique muscle dysfunction → appropriate reoperation. Reoperation rate is 15–30%1).
Ciancia syndrome: Characterized by large-angle esotropia >60°, abduction limitation, adduction fixation, and face turn. Set the recession amount larger than usual.
Ultra-early surgery before 8 months of age is considered most advantageous for achieving fusion (near fusion 93.8%) and stereopsis (75.0%). Early surgery by 2 years of age can also be expected to yield good results. Large-angle esotropia of 40Δ or more does not resolve spontaneously, so it is important to consult a pediatric ophthalmologist early to determine surgical indication1).
In infantile esotropia, the reoperation rate is reported to be 15–30%1). If DVD or oblique muscle dysfunction becomes manifest postoperatively, additional surgery is considered as appropriate. Residual esotropia (≥8Δ) is managed with membrane prism. Long-term management into adulthood is required; the success rate is about 80% after the first surgery and exceeds 95% including reoperations8).
Refractive accommodative esotropia: Full hyperopic correction with glasses is the first choice, and surgery is not required. Ocular alignment stabilizes within 3 months of wearing glasses. Only about 15% eventually become glasses-free. Since hyperopic power peaks around 6–7 years of age, regular cycloplegic refraction is necessary. Full-time wear is essential, and care must be taken to prevent the glasses frame from slipping down.
Non-refractive accommodative esotropia: Prescribe bifocal lenses with +2.5 to +3.0D addition or progressive addition lenses. Around 8–12 years of age, 37–62.5% can switch from bifocal to single vision lenses. Cholinesterase inhibitor distigmine bromide eye drops (Ubretid 1%) may be effective in reducing the AC/A ratio.
Partially accommodative esotropia: If 10PD or more remains under full correction with glasses, surgery is indicated. Surgery is performed only for the angle measured with glasses. About 30% require surgery. In children under 7 years, repeat cycloplegic refraction before surgery to confirm no undercorrection due to increased hyperopia. Surgical procedures include bilateral medial rectus recession, unilateral recession-resection, and posterior fixation suture (Faden procedure: effective for high AC/A ratio).
Refractive accommodative esotropia can achieve orthophoria with full hyperopic correction glasses alone. However, only about 15% eventually become glasses-free, and most require continued wear. In partially accommodative esotropia, glasses alone are insufficient, and surgery is needed for the residual deviation.
In Japan, type A botulinum toxin (Botox®) was approved for strabismus treatment in 2015 (insurance coverage for ages 12 and older) 9). In the four years after approval, approximately 1,500 procedures were performed 9). Physician requirements: Board-certified ophthalmologist by the Japanese Ophthalmological Society + completion of training course + experience in 50 or more muscle surgeries 9).
Injection into the medial rectus for acute sixth nerve palsy in children (recommended dose 2.5–5 units per muscle) has been reported to improve from 50 PD to 20 PD in one week and to orthophoria in eight weeks 7). In infantile esotropia, it is more effective for deviation angles less than 30–35Δ 1). Safety has not been established for strabismus over 50 PD, restrictive strabismus, or Duane syndrome with lateral rectus weakness.
Hyperopia (+2D or more) requires accommodation to focus a clear image on the fovea, and increased accommodation leads to increased accommodative convergence. Normally, fusional divergence compensates for this convergence, but when it exceeds the compensatory ability, esotropia becomes manifest. In refractive type, the AC/A ratio is normal (4±2PD/D) but the amount of accommodation is excessive. In non-refractive type (high AC/A ratio), the AC/A ratio reaches ≥6PD/D, and convergence associated with accommodation at near becomes excessive, resulting in marked esotropia at near.
Age-related changes in hyperopia are also important. Newborns have about +2D of hyperopia, and hyperopia tends to increase until around 7–8 years of age. This increase and decrease affect the onset and course of accommodative esotropia.
The cause of infantile esotropia is unknown, and several hypotheses exist.
Richards (2007) reported that when esotropia persists for more than 6 months, monocular connections increase threefold compared to binocular connections 1). In primate models, early eye alignment restored normal eye movements and binocular vision, while delayed correction resulted in residual esotropia, LN, DVD, and OKN asymmetry 1).
| Type | Main Mechanism |
|---|---|
| Refractive accommodative esotropia | Hyperopia → increased accommodation → convergence reflex → decompensation of fusional divergence → esotropia |
| Non-refractive accommodative esotropia | High AC/A ratio (≥6PD/D) → excessive convergence at near |
| Infantile esotropia | Fusion deficiency, optokinetic asymmetry (unknown cause). Impaired binocular vision development during the sensitive period |
| Nystagmus blockage syndrome | Infantile nystagmus suppressed by convergence → excessive convergence → esotropia. ENG shows decelerating slow-phase waveform |
| IMCE | Sustained near gaze → shortening of medial rectus, anterior displacement of insertion. Pathological reports of lateral rectus atrophy exist 6) |
| AACE type V | Posterior fossa lesion → compression of cranial nerve VI 2) |
Mechanism of amblyopia: In constant esotropia, the image from the deviated eye is suppressed in the cerebral cortex. When fixation is consistently with one eye, sustained suppression of the non-dominant eye leads to strabismic amblyopia. If alternating fixation occurs, both eyes develop equally.
Evidence from multicenter studies on ultra-early surgery has been accumulating.
| Study | Main Findings |
|---|---|
| Birch & Stager 20001) | Surgery before 6 months: stereopsis 100% vs after 1 year: 8% |
| ELISS 20051) | Early group 13.5% vs late group 3.9% (p<0.01) |
| Yagasaki 20201) | Ultra-early 77% vs early 20% vs late 13% |
| Yagasaki 20111) | Ultra-early: all DVD cases latent vs late: 38.9% manifest |
| Shin 20141) | Late surgery → spontaneous DVD OR=8.23 (P<0.001) |
| Gerth 20081) | Surgery before 11 months → normal mVEP vs 11-18 months → abnormal mVEP persists |
| Drover 20081) | Postoperative improvement in sensorimotor and gross motor development confirmed |
Ghobrial & Kuwera (2023) reported improvement after asymmetric recession-shortening surgery in a case of bilateral horizontal gaze palsy and esotropia following neurocysticercosis3). When preoperative differentiation between gaze palsy and abducens nerve palsy is difficult, recess-resect surgery is recommended.
Negishi et al. (2024) reported esotropia surgery in nanophthalmos (axial length 15.5 mm)5). With a 6 mm medial rectus recession, the expected correction of 25 PD was only 12 PD, suggesting the influence of biomechanical peculiarities and pulley effects in small eyes.
The increase in AACE and IMCE due to excessive digital device use has recently gained attention, and the public health significance of limiting near work is being discussed2, 6). New approaches to improve binocular vision (binocular treatment: dichoptic stimulation to draw attention to the amblyopic eye) are being developed for strabismic amblyopia4). In adults with accommodative esotropia, LASIK/PRK to correct hyperopia and eliminate glasses has been attempted, but its application in children is not established. The success rate of surgery in adults is about 80% for the first surgery and over 95% including reoperations8).
