In some families the condition is associated with variants in the Chimerin 1 gene and in others it is associated with variants in the Transcription factor MafB gene. Diagnosis
Classification
Duanes syndrome has three variants:

Type I: Limited abduction with or without esotropia
Type II: Limited adduction with or without exotropia
Type III: Limitation of both abduction and adduction and any form of horizontal strabismusBrown(1950) has classified Duanes syndrome according to the characteristics of the limitation of movement-

Type A: with limited abduction and less-marked limitation of adduction
Type B: showing limited abduction but normal adduction
Type C: the limitation of adduction exceeds the limitation of abduction. There is an exotropic deviation and a head turn to compensate the loss of adductionThe first type is more common and accounts for 85% of the cases. Differential diagnosis
In the clinical setting, the principal difficulties in differential diagnosis arise as a consequence of the very early age at which patients with this condition first present. The clinician must be persistent in examining abduction and adduction, and in looking for any associated palpebral fissure changes or head postures, when attempting to determine whether what often presents as a common childhood squint (note-"squint" is a British term for two eyes not looking in the same direction) is in fact Duane syndrome. Fissure changes, and the other associated characteristics of Duanes such as up or down shoots and globe retraction, are also vital when deciding whether any abduction limitation is the result of Duanes and not a consequence of VI or abducens cranial nerve palsy.
Ametropic amblyopia is a medical condition in which the retina cannot focus on the image of a distant object, a condition often described as reduced visual acuity. This is due to large uncorrected refractive errors in the patients optic system of the eyes. Astigmatism is one of the most frequent causes of ametropic amblyopia. References
Further reading
Moseley, Merrick J., et al. "Effectiveness of occlusion therapy in ametropic amblyopia: a pilot study." British Journal of Ophthalmology 81.11 (1997): 956–961. Cavazos, H.;  et al. (1993). "Ametropic Amblyopia". Strabismus. Informa Plc. 1 (2): 63–67. doi:10.3109/09273979309087719. PMID 21314500. Abraham, S. V. "Bilateral ametropic amblyopia." J Pediatr Ophthalmol Strabismus 1 (1964): 57–61. Werner, D. B., and W. E. Scott. "Amblyopia case reports--bilateral hypermetropic ametropic amblyopia." Journal of pediatric ophthalmology and strabismus 22.5 (1984): 203–205. Moseley, Merrick J;  et al. (1997). "Effectiveness of occlusion therapy in ametropic amblyopia: a pilot study". British Journal of Ophthalmology. BMJ Publishing Group Ltd. 81 (11): 956–961. doi:10.1136/bjo.81.11.956. PMC 1722055. PMID 9505818.