Without necessarily going into Joseph Lang’s theories (and Joseph is a friend of mine), I will offer this:

Infantile or congenital esotropia patients have a basic motor fusion defect with an abnormal vergence response. If the eyes are aligned very early, sensory fusion can be achieved but it usually does not last and when it does, the sensory fusion is not normal but some have reported it. At best, normal fusion in these patients is very, very rarely seen. You might even say if sensory response is normal, the patient does not have congenital ET. The abnormal vergence response is seen clearly in Ciancia syndrome. These patients have abduction nystagmus and prefer fixing with an adducted eye with the face turned toward this fixing eye. This has also been called cross fixation. It has also been my experience that every patient with congenital or infantile esotropia has asymmetric optokinetic nystagmus. This is demonstrated by normal patterns with temporal to nasal stripe rotation and coarse movements when stripes are rotated from nasal to temporal. This vergence anomaly is what I believe leads to the variety of abnormal head postures that these children show. Not all of these patients have abnormal head posture, but all have asymmetric OKN!

In the order of occurrence for congenital ET:

1. Asymmetric OKN -- always
2. ET -- almost always ( I saw one patient with asymmetric OKN and DVD, but straight eyes and moderate stereo acuity. His brother had congenital ET. I called this patient congenital ET without ET and reported it.)
3. DVD
4. Abnormal head posture