Apparent inferior rectus palsy with gaze-dependent sensory adaptations.

Purpose: This report presents a case of apparent congenital inferior rectus palsy notable for sensory adaptations that appeared to vary with direction of gaze. It is shown that readily available clinical tests and an understanding of the physiology of ocular motility can be used to help distinguish from differential diagnoses such as contralateral inferior oblique palsy or the more commonly seen Brown syndrome.

Case Report: A 20-year-old male optometry student reported strabismus that had been noted at birth and was diagnosed as Brown syndrome in childhood. The Parks three-step test showed primary gaze hypertropia that increased in left gaze but the "third step" (Bielschowsky head tilt test) was not successful in establishing the apparently correct diagnosis, which was later confirmed by a Hess screen. A proposed "fourth" step by Bajandas proved to be more accurate in this case of inferior rectus palsy. Sensory tests revealed adaptation patterns that varied with gaze direction and showed a cyclotorsional element. The patient reported being relatively unconcerned about his condition as he seemed to be able to voluntarily use a form of shallow suppression to reduce awareness of diplopic images.

Conclusions: Although it is common to consider suppression and retinal correspondence status as hardwired and relatively constant for an individual patient, this case demonstrates that these sensory adaptations are likely to be far more complex and transitory. An understanding of both motor and sensory repercussions of ocular motility dysfunction assists differentiation between benign and sinister causes of nonconcomitant strabismus.