Fixation dysfunction with intermittent saccadic intrusions managed by yoked prisms: a case report

A 44-year-old woman came to us with a chief symptom of "jumping letters side-to-side, which is most noticeable while reading." The onset occurred after she had experienced a closed head traumatic brain injury 3 years earlier. Several neuro-ophthalmologists diagnosed a fixational instability secondary to saccadic intrusions and prescribed Gabapentin, which provided minimal relief.

The term saccadic intrusions refers to an inappropriate saccade with a disrupting effect on fixation. Our examination revealed a myopic anisometropia. Motility testing confirmed saccadic intrusions that lessened on occlusion of either eye and superior gaze. A plano spectacle with six-prism diopter-yoked base down was used to position the eyes in the superior null point. Electro-oculography, using the Visagraph II, demonstrated pre and post changes with the prism. The uncorrected anisometropia allowed the patient to be monocular under binocular viewing conditions.

The case report focuses on fixational problems that may occur secondary to traumatic brain injuries. There is evidence that the origin of the problem may be from uninhibited brain stem circuits. Pharmacological treatment may only offer transient improvement. The responsibility of a functional cure is often placed on the optometrist.

This case demonstrates how an alternative use of prism and prescription application can play an important role in the management of fixation dysfunctions.