Distinct visually evoked eye movement phenotypes in Frmd7 and Chrnb2 mutant mice

The optokinetic reflex stabilizes retinal images during global motion and depends on retinal direction-selective (DS) circuits. Although mutant mouse strains exhibit impaired DS circuits via distinct mechanisms, how these circuit disruptions produce distinct visually evoked eye movement phenotypes remain unclear. Here, we developed a behavioral system to quantify mouse eye movements under opposite-direction and same-direction visual stimuli. Using this platform, we examined eye movement responses in wild-type (WT) mice and two DS circuit mutants: Frmd7^tm mice, which lack horizontal DS tuning and horizontal eye movement responses, and Chrnb2^tm mice, which have disrupted β2-nAChR-dependent cholinergic spontaneous activity during development. Consistent with previous research, both mutants lacked horizontal eye movement responses across conditions, while vertical responses remained detectable. We found that Chrnb2^tm mice exhibited spontaneous horizontal eye oscillations regardless of visual input. This phenotype was absent in Frmd7^tm mice, suggesting that defective retinal waves in Chrnb2^tm mice may induce instability distinct from the loss of horizontal DS tuning alone. In addition, binocular opposite-direction stimulation enhanced vertical responses only in WT mice. Together, these findings provide a functional comparison of Frmd7^tm and Chrnb2^tm mice and establish a quantitative framework for dissecting how genetic perturbations alter the retinal computations underlying horizontal and vertical eye movements.