Stephen Heinen¹ (heinen@ski.org), Devashish Singh¹, Scott Watamaniuk^1,2; ¹Smith-Kettlewell Eye Research Institute, ²Wright State University

We have previously shown in normals that an occluded eye moves unpredictably during midline pursuit (Chandna et al., 2021) but moves with the viewing eye during tangent screen pursuit (Heinen et al., 2024). These results suggest that the eyes are controlled independently for vergence, while a unitary signal drives conjugate movements. Here we test the contributions of independent and unitary signals to the pursuit signal by recording from a patient blind in one eye. This unique case allows us to study pure monocular viewing not present when occluding an eye. The patient (57 YO female) had late-onset blindness in one eye due to retinal ischemia and corrected-to-normal acuity in the seeing eye. For midline pursuit, an accommodative stimulus, a central letter “X” (0.34 deg at 67 cm) was surrounded by a peripheral letter array and moved back and forth periodically. For tangent screen pursuit, a dot (0.34 deg at 57 cm) moved left and right across the screen periodically. Eye movements were measured with an EyeLink 1000. We found that the seeing eye followed the target accurately in both paradigms. However, while the blind eye exhibited vergence during midline pursuit, its amplitude and temporal relationship with the seeing eye were highly variable. In contrast, the blind eye moved accurately and was temporally synchronized with the seeing eye during tangent-screen pursuit. The results provide additional evidence that while a single command does not drive the eyes during vergence, a single command does appear to drive them during conjugate eye movements. We believe the blind eye is controlled without vision by relying on an imperfect cortical representation of the target (a “virtual target”) derived from input from both eyes. The results have implications for oculomotor neural pathways, and clinical strabismus interventions.

Acknowledgements: Supported by NIH R01EY034626, Smith-Kettlewell Eye Research Institute and Wright State University