A covered eye fails to follow an object moving in depth

Abstract

To clearly view approaching objects, the eyes rotate inward (vergence), and the intraocular lenses focus (accommodation). Current ocular control models assume both eyes are driven by unitary vergence and unitary accommodation commands that causally interact. The models typically describe discrete gaze shifts to non-accommodative targets performed under laboratory conditions. We probe these unitary signals using a physical stimulus moving in depth on the midline while recording vergence and accommodation simultaneously from both eyes in normal observers. Using monocular viewing, retinal disparity is removed, leaving only monocular cues for interpreting the object’s motion in depth. The viewing eye always followed the target’s motion. However, the occluded eye did not follow the target, and surprisingly, rotated out of phase with it. In contrast, accommodation in both eyes was synchronized with the target under monocular viewing. The results challenge existing unitary vergence command theories, and causal accommodation-vergence linkage.

Asymmetric eye movements during fixation challenge Hering’s Law of a unitary neural command

“…Despite that Helmholtz's opposing theory was postulated contemporaneously with Hering's, critical experiments differentiating these theories are lacking, and Hering's theory has managed to prevail for over 150 years. However, recent results of experiments comparing oculomotor behavior of both eyes during monocular viewing challenge Hering's Law [23]. This study found asymmetric behavior between the two eyes during smooth pursuit of a midline target, evidence that the eyes are not yoked.…”

“…This study was conducted to investigate xation behavior of both eyes under binocular and monocular viewing. We wished to determine whether the eyes behaved the same or differently motivated by results of previous work showing asynchronous and unpredictable behavior of an occluded eye during midline pursuit [23].…”

“…Stimuli. Participants xated on a modi ed, digital version of the letter array used in our previous pursuit vergence experiments [23](Fig. 1).…”

“…Occlusion. Participants were occluded using an IR-pass occluder, cutoff ~ 750 nm (ePlastics, San Diego, CA) a xed to one side of a pair of eye glass frames (right or left eye occluded) [23]. Data Analysis.…”

“…Here we investigate in neurotypicals whether the magnitude of the area of xation excursion and the component FEMs are the same or different for each eye during xation. We employed the similar methodology as in Chandna et al (2021) of recording both eyes simultaneously during binocular and monocular viewing. Interestingly, we found differences in the variability and speed of ocular drift, and the magnitude of microsaccades between the two eyes, yet microsaccades always occurred in both eyes at the same time and in the same direction.…”