unilateral strabismus

Unilateral strabismus is a heterotropia in which the patient habitually fixates with the same eye, so the other eye remains deviated. In alternating strabismus the patient fixates with either eye, and fixation habits form a spectrum between the two.¹ The deviated eye takes up fixation only when the fixating eye is covered.²

Diplopia occurs in strabismus because corresponding retinal elements receive different images. The patient suppresses the fovea of the deviated eye to avoid confusion, and develops either peripheral suppression or anomalous retinal correspondence to avoid diplopia.³ Constant unilateral suppression leads to strabismic amblyopia.³ Strabismic amblyopia occurs with a constant, unilateral strabismus that begins before 6 years of age, while intermittent and alternating deviations rarely cause amblyopia.⁴