Which law explains yoked muscles between eyes?

• A. Sherrington's Law
• B. Donder's Law
• C. Troxler Effect
• D. Hering's Law of Equal Innervation

Answer: (D)

The idea here is that the brain sends equal neural drive to the paired muscles that move both eyes in the same direction, so the eyes gaze together in a coordinated, conjugate way. These paired muscles, one in each eye, are yoked to produce the same movement. For instance, when you shift gaze to the left, the left eye uses its lateral rectus and the right eye uses its medial rectus, and they receive the same amount of innervation so both eyes move left in harmony.

This explains normal binocular alignment and why misalignment occurs when the signal to one eye’s yoked muscle is disrupted, leading to diplopia. It’s distinct from other ideas about eye movement: Sherrington’s law deals with reciprocal innervation between agonist and antagonist within a single eye, not coordination between the two eyes; Donder’s law is about the amount of innervation for a given eye position regardless of the path taken; the Troxler Effect is a perceptual fading phenomenon unrelated to motor innervation.