Cocaine requires intact sympathetic pathways innervating the iris dilator muscle. Little or no pupillary response to 1% pilocarpine indicates muscarinic receptor blockade or a traumatic pupil.Ĭocaine (4% to 10%) eyedrops cause a sympathomimetic effect by blocking the neuronal uptake of norepinephrine (NE) into prejunctional sympathetic nerves, prolonging the action of this neurotransmitter to stimulate the dilator muscle of the iris. Constriction of the pupil caused by 1% pilocarpine suggests CN III nerve palsy. An increased or supersensitivity of pupillary constriction to a weak cholinergic agonist, 0.1% pilocarpine or 2.5% methacholine, is diagnostic for Adie's tonic pupil Lowenfeld (1967). These cholinergic muscarinic receptor agonist cause contraction of the iris sphincter muscle and ciliary muscle. These are applied topically to the eye and are used in developing a differential diagnosis for the fixed, dilated pupil. Children with light colored eyes will not develop this heterochromia. A characteristic of congenital Horner syndrome in some patients is the development in later childhood or adolescence of iris heterochromia, with the affected iris being lighter in color. If the ruler moves smoothly, anhidrosis is present because small amounts of perspiration will cause the ruler to stick and have a jerking motion. Anhidrosis of the forehead may be assessed by lightly rubbing a smooth plastic ruler across the forehead skin. Anhidrosis of the ipsilateral side of the body, side of the face, or forehead may be present, depending on the site of the innervation defect. The lower eyelid on the affected side may rest 1 mm higher than the fellow lid (upside-down ptosis), and the narrowed palpebral fissure gives the appearance of enophthalmos (see Fig. Paresis of Müller muscle of the lid leads to the mild upper lid ptosis seen in Horner syndrome. A ruler or pupil gauge with circles or half circles or different diameters is useful as a reference to accurately determine the pupil sizes. As the light remains dimmed, the magnitude of the anisocoria may decrease but it will still be greater than that observed when the light was bright. Immediately on dimming of the light in Horner syndrome, one pupil will dilate more slowly than the other and the magnitude of the anisocoria will be observed to increase (dilation lag). With the light on, both pupils will be miotic and some anisocoria may be observed. The anisocoria of Horner syndrome is best examined with the patient fixating on a distance object and observing both pupils as a bright light is alternately turned on and off. The light and near pupillary reactions are intact.

The anisocoria of Horner syndrome is more apparent in dim illumination, and the affected pupil shows a lag in dilation on dimming of the lights. The classic triad of findings includes ptosis, miosis, and anhidrosis on the affected side.

Pharmacologic miosis occurs with echothiophate iodide or pilocarpine.Ī lesion at any point along the sympathetic pathway for pupillary constriction results in Horner syndrome. Pharmacologic testing with 1% pilocarpine is useful for differentiating pharmacologic mydriasis from third cranial nerve palsy pupillary constriction occurs in third nerve palsy and does not occur with pharmacologic mydriasis. Pharmacologic mydriasis may occur with minimal exposure to atropine, cyclopentolate, or other parasympatholytic agents (e.g., accidental exposure to some pesticides). In cases of brainstem herniation and basilar meningitis, however, pupillary dilation may be the only sign of third nerve palsy. Pupillary involvement in third nerve palsy is usually accompanied by ptosis and disturbances in ocular motility. Lesions of the parasympathetic or sympathetic system, if unilateral or asymmetrical, cause pupillary constriction or dilation and produce pupils that are unequal in size, termed anisocoria. Zitelli MD, in Zitelli and Davis' Atlas of Pediatric Physical Diagnosis, 2018 Anisocoria

Causes of unequal pupil size