Hering's law of equal innervation

Hering's law of equal innervation is used to explain the conjugacy of saccadic eye movement in stereoptic animals.

[2][3] The 11th century scholar Ibn al-Haytham stated that eyes move together and equally so that the visual axes converge on an object of interest in his Book of Optics.

[4] Hering's law of equal innervation is best understood with Johannes Peter Müller's stimulus where an observer refoveates a point that moved in one eye only.

Thus Hering's law, in its original formulation, simply cannot be correct as it would lead to situations where the eyes would move by different amounts, something on which both agreed never happens.

Hering subsequently modified his law to state that the eyes behave as if they received equal innervation.