Substance P in the human iris: possible involvement in echothiophate-induced miosis in cluster headache

Dim the Lights: A Narrative Review of Photophobia in Migraine

A preference for darkness is one of the main associated features in people with migraine, the cause remaining a mystery until some decades ago. In this article, we describe the epidemiology of photophobia in migraine and explain the pathophysiological mechanisms following an anatomical structure. In addition, we review the current management of migraine and photophobia. Ongoing characterization of patients with photophobia and its different manifestations continues to increase our understanding of the intricate pathophysiology of migraine and vice versa. Detailed phenotyping of the patient with photophobia is encouraged.

SUNCT syndrome with paroxysmal mydriasis: Clinical and pupillometric findings

SUNCT syndrome (short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing) is a primary headache characterised by a high frequency of attacks associated with marked autonomic periocular signs and symptoms. Activation of the hypothalamus via the superior salivary nucleus is probably responsible for some of the autonomic involvement observed during SUNCT attacks. We describe a case of SUNCT with unusual autonomic features (e.g., mydriasis) and early onset. Pupillometric studies were performed both in a basal condition (without anisocoria) and after instillation of phenylephrine (a drug with direct sympathomimetic activity) and pilocarpine (a parasympathetic agonist).

The findings in this patient seem to indicate involvement of the ocular sympathetic supply in SUNCT, responsible for the mydriasis, and seem to strengthen the possibility that the autonomic phenomena in this syndrome vary with different levels of pain severity.

Pupillary abnormalities due to sympathetic dysfunction in different forms of idiopathic headache

Idiopathic vascular-type headache is frequently associated with pupillary alteration, which is often presumed to be due to malfunction of the sympathetic nervous system. In this review the anatomical and neurotransmitter basis of oculosympathetic function is briefly discussed along with some of the common pharmacological and physiological pupillary tests used in its assessment. The clinical and subclinical features of the pupil abnormalities are analysed in idiopathic headache, which includes migraine, tension headache, cluster headache, and chronic paroxysmal hemicrania. Possible mechanisms underlying these alterations are suggested. Among secondary headaches, carotid dissection and aneurysm have to be excluded when unilateral headache is associated with a persistent ipsilateral oculosympathetic deficit. From the literature, specific responses to pupillary tests apparently are present in idiopathic headache. Pupillary tests may differentiate between the subtypes of idiopathic headache. The investigation of pupillary dysfunction may provide information on the physiopathological basis of headache.

In vivo pupillary constrictor effects of substance P in man

The ocular effects of substance P (SP) were studied in 13 normal volunteers. Various concentrations of SP (0.135, 1.35 and 135 micrograms per 100 microliters) were instilled into the conjunctival sac and pupillary area changes were evaluated by means of an electronic pupillometer. The ability of SP to modify the mydriasis induced by pretreatment with 1% homatropine eyedrops was also studied. The instillation of SP produced miosis in a dose-dependent manner without provoking any ocular disturbances. Furthermore, the highest concentration tested was unable to reduce the homatropine-induced mydriasis. These findings indicate that SP exerts a pupillokinetic action in humans which probably occurs via a receptor mechanism. Since muscarinic blockade is not overcome by the peptide instillation, the results do not clarify whether SP causes miosis acting on iris muscles and/or cholinergic fibres.

Possible non-muscarinic miotic action of echothiophate iodide in humans

The proposed non-muscarinic pupillary action of echothiophate iodide (EI) was investigated in humans. In 10 healthy volunteers the variations of the pupillary area, induced by EI eye drops, were evaluated by using an electronic pupillometer. When instilled alone, as well as after homatropine, EI caused pupillary constriction. The reduction of the homatropine-induced mydriasis by EI was not accompanied by any increase in the almost abolished pupillary response to light, thus excluding that an enhancement of the parasympathetic activity contributes to pupillary constriction. These findings suggest a non-muscarinic component in the EI-induced miosis, the nature of which remains to be elucidated.