fixating eye
In a heterotropia, the fixating eye is the eye that holds fixation on the target, and the fellow eye is the deviated eye.1 Covering the fixating eye makes the deviated eye move out of its heterotropic position to take up fixation, and the cover test looks for this movement.1 A patient with a unilateral heterotropia habitually fixates with one eye, and a patient with an alternating heterotropia fixates with either eye.2
The fixating eye sets the innervation to both eyes, and the angle of a paretic strabismus therefore varies with the eye used for fixation.3 The deviation measured with the normal eye fixating is the primary deviation, and the deviation with the paretic eye fixating is the secondary deviation, the larger of the two.3
Fixation preference also gives a practical estimate of amblyopia in a child too young for an acuity chart.4 A child who strongly objects to cover over the fixating eye but accepts cover over the deviated eye probably has severely reduced acuity in the deviated eye.4 Free alternation of fixation suggests that amblyopia is absent.4
Sources (8)
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 12
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 8
- Kanski, Clinical Ophthalmology (2024), ch. 18
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 14
- Rutstein, R., Daum, K. (1997). Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- Kushner, B. J. (2017). Diagnosis and treatment of diplopia. In Pediatric Ophthalmology and Strabismus (pp. 1023-1046). Springer, Berlin, Heidelberg.
- Mohney, B. G. (2014). Common forms of childhood esotropia. Ophthalmology, 121(1), 376-380.
- Gunton, K. B. (2015). Dissociated vertical deviation: clinical features, associated abnormalities, and a new pathogenetic concept. Eye, 29(2), 213-220.
Reviewed October 2026