Unusual, as the deviation is often intermittent and there is some binocular fusion. Unless strong fixation preference is present, do not treat with patching, which could break down weak fusion. Treat amblyopia by patching the dominant eye 2–4 h a day until the patient holds fixation well with the nondominant eye. Follow up every 1–2 weeks to test for change in fixation preference. A week or two of patching can reverse fixation preference in these young infants.

Use cyclopentolate 1 % (one or two doses, 5 min apart). Refract 30 min after the last dose.

A complete ocular examination, including a dilated retinal exam, is important to rule out a sensory esotropia. Sensory esotropia can be caused by an infantile cataract, retinoblastoma, optic nerve hypoplasia, or any other cause of infantile visual loss.

Surgery is based on the near deviation, as this is the most reliable measurement in these young children. Bilateral medial rectus (MR) recessions are preferred because the deviation is usually comitant. If there is unilateral vision loss, then a monocular recession-tightening procedure is performed on the poor-seeing eye.

Normal children and adults have precise and symmetrical smooth pursuit for following an object moving slowly from side to side. Infants, however, have smooth pursuit asymmetry, with a deficiency in nasal-to-temporal smooth pursuit, compared with pursuit following an object moving in a temporal-to-nasal direction. The nasal-to-temporal–directed smooth pursuit will lag behind the target, and saccadic movements intrude to catch up. This asymmetry is demonstrated only during monocular viewing. Smooth pursuit asymmetry is a manifestation of visual motor immaturity and naturally resolves as motor fusion develops by 4–6 months of age. Patients with disorders that disrupt binocular visual development, such as congenital esotropia or unilateral congenital cataract, retain smooth pursuit asymmetry throughout life, despite surgery [2]. Thus, the presence of smooth pursuit asymmetry in older children and adults with esotropia is a sign of neonatal onset with early disruption of binocular visual development.

Mild (−1) limitation of abduction is common and does not indicate a lateral rectus paresis. Try the doll’s head maneuver or spinning the child (vestibular stimulation) to elicit full abduction. Intact abduction saccadic eye movements in the face of mild limitation of abduction indicate good lateral rectus function and a tight medial rectus muscle.

Check for inferior oblique overaction and V pattern.

Check fixation preference. Strong preference for one eye indicates amblyopia.

Prism alternate cover testing is best, but use Krimsky testing for verification or if prism cover testing is unobtainable. Surgery is usually based on the near deviation, which is the most reliable in infants. When possible, measure the distance and near deviation.

Use cyclopentolate 1 % (one or two doses, 5 min apart). Refract 30 min after the last dose.

Most references recommend that surgery for congenital esotropia be performed between 6 months and 1 year of age in order to achieve peripheral fusion and low-grade stereo acuity. This author (KWW) reported experience with very early surgery showing that surgical correction between 3 and 4 months of age can result in high-grade stereo acuity [3]. Early surgery should be considered if there is a constant large-angle esotropia (≥40 PD) with the angle stable or increasing on at least two examinations, 2 or more weeks apart. The CEOS showed that spontaneous resolution was rare (<4 %) if these parameters were met [4]. Intermittent small-angle esotropia, on the other hand, will resolve in approximately one third of cases, so it is better to wait until these patients are at least 6 months of age before considering surgery.

The procedure of choice is bilateral medial rectus (MR) muscle recessions using the near deviation as the target angle. (Use surgical chart in Appendix for specific numbers.) The standard surgical chart numbers are designed to give infants with infantile esotropia a slight immediate overcorrection, which is desirable, as convergence will pull the eyes straight. (See Sect. 3.2.4.4 below.). In older patients and adults with long-standing congenital esotropia, the chart numbers may give a slight undercorrection. This is desirable, as these patients usually have poor fusion potential and tend to drift to exotropia over time. Thus the surgical chart numbers can be used for all ages, as they tend to self-adjust for age. Patients with irreversible dense amblyopia should have monocular surgery (recession-tightening procedure) on the amblyopic eye to protect the “good eye.”

The immediate postoperative goal is a small exotropia (5–10 PD) for infants with possible fusion potential. We naturally have strong, innate fusional convergence (>30 PD), so a small exotropia is “good” because it can be fused. A small esotropia, on the other hand, is difficult to fuse, as our divergence amplitudes are weak (approximately 8 PD).

Dr. Marshall Parks, during his studies on monofixation syndrome and peripheral fusion, found that in order to develop binocular fusion, the eyes must be within 8–10 PD of orthotropia. The goal of surgery is to align the eyes during early infancy to within 8–10 PD, to stimulate the development of binocular fusion. The closer the alignment to orthotropia, the better the sensory outcome. An esotropia larger than 8–10 PD will not allow binocular fusion (not even peripheral fusion). A residual esotropia larger than 10 PD should be considered for further treatment. (See next section.) Patients with a poor prognosis for binocular fusion (e.g., dense irreversible amblyopia, or uncorrected congenital esotropia in a patient more than 2 years old) should be considered for surgery based on cosmetic indications.