What is the pupillary response when there is a lesion in the optic nerve?

In the case of a lesion in the optic nerve, the pupillary response can be affected due to the optic nerve's role in transmitting visual information to the brain, which also mediates the pupillary reflex. When there is damage to the optic nerve, particularly in a unilateral lesion, the affected eye is unable to process visual stimuli accurately, leading to an absence of the direct pupillary reflex on that side.

While both eyes are still capable of constricting in response to light due to the consensual reflex, the malfunction in the damaged optic nerve prevents the affected eye from responding normally to light input. Therefore, in a scenario where light is shone in the affected eye, there will be no constriction observed. This is because the afferent pathway for the pupillary reflex, which includes the optic nerve, is compromised.

In the healthy eye, however, because it still receives proper visual input through an intact optic nerve, you would typically see a normal pupillary reaction. Thus, the correct response when considering the affected side is that there is no pupillary reflex on that side due to the lesion damaging the optic nerve.