Ex vivo isometric force measurements in mouse EOMs. (A) Representative trace of the absolute twitch force obtained from isolated single extraocular rectus muscles from WT (black line; n = 8) and ryr3^−/− (gray line, n = 9) muscles. Muscles were stimulated by electric field stimulation with a pulse of 24.6 V having a duration of 0.5 ms. (B) Objective classification of force measurements into four groups. The force was normalized to the maximum of each transient to illustrate the differences in the kinetics as well as the presence or absence of the fast and slow component of the twitch. (C) Kinetic twitch parameters (TTHP, TTP, and HRT). Each symbol represents the kinetic parameters of a single rectus EOM from a single mouse; empty circles, WT mice; gray circles, ryr3^−/− mice. *, P < 0.05; **, P < 0.001; ****, P < 0.0001, Student’s t test. Experiments were performed at room temperature. (D) Principal-component analyses of five twitch parameters (slow amplitude, fast amplitude, TTHP, TTP, and HRT). The axes represent the two principal components.