A Consensual response is any reflex

Reflex

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

 observed on one side of the body when the other side has been stimulated.

For example, if an individual's right eye is shielded and light shines into the left eye, constriction of the right pupil will occur, as well as the left. The reasoning for this response is that if a light source

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

is intense, both pupils would probably be illuminated and it follows that they would constrict together.