Pupil fails to dilate by giving cocaine in –

In periphery cocaine blocks the uptake of Adrenaline and Noradrenaline in Adrenergic nerve ending resulting in higher concentration of sympathetic neurotransmitters (Sympathomimetic effect) : The peripheral sympathomimetic action of cocaine produces following effect : Mydriasis Rise in B.P. Local vasoconstriction Tachycardia Therefore if the peripheral sympathetic system is paralysed it will lead to reverse of the above mentioned actions.