Adrenergic mydriasis

Thompson HS, Menscher JH. Adrenergic mydriasis in Horner s syndrome hydroxyamphetamine test for diagnosis of postganglionic defects.AmJ Ophthalmol 1971 72 472-480. 

The following sections consider the most common disorders associated with a unilateral fixed and dilated pupil, including third-nerve palsy, anticholinergic mydriasis, iris sphincter atrophy, and adrenergic mydriasis. Because a dilated pupil does not always characterize Adie s syndrome, this disorder has been discussed separately. 

A special feature of the iris is its autonomic innervation. Sympathetic activation widens the aperture of the iris whereas impulses from the parasympa thetic nervous system decrease the aperture size. Therefore adrenergic agonists and anticholinergic compounds both increase the aperture of the iris, i.e., cause mydriasis, and antiadrenergic and cholinergic agonists decrease it, i.e., cause miosis. The iris can thus be considered an excellent mirror reflecting the balance of the autonomic nervous system in the body. " ... 

Dapiprazole acts by blocking die a-adrenergic receptor in smootii muscle and produces miosis through an effect on the dilator muscle of the iris. The drug is used primarily after ophtiialmic examinations to reverse the diagnostic mydriasis (dilation of the pupil). 

Khat produces sympathomimetic effects, increasing heart rate and blood pressure. When khat is chewed, the increases are gradual, maximizing at about 2 hours and lasting for 4 hours. However, tolerance develops to blood pressure and heart rate effects in habitual users. Mydriasis and increases in respiration also occur. Cathinone induces thermogenesis in brown adipose tissue, which is mediated by jS-adrenergic receptors (Tariq et al. 1989). 

Uses Mydriasis, ocular redness [OTC], periop mydriasis, posterior synechiae, uveitis w/ posterior synechiae Action a-Adrenergic agonist Dose Adults. Redness 1 gtt 0.12% q3-4h PRN Exam mydriasis 1 gtt 2.5% (15 min-1 h for effect) Preop 1 gtt 2.5—10% 30-60 min preop Ocular disorders 1 gtt 2.5-10% daily-tid Peds. As adult, only use 2.5% for exam, preop, and ocular conditions Caution [C (may cause late-term fetal anoxia/bradycardia), +/-] HTN, w/ elderly w/ CAD Contra NAG Disp Ophth soln SE Tearing, HA, irritation, eye pain, photophobia, arrhythmia, tremor EMS None OD Unlikely but may cause exaggeration of nl SEs symptomatic and supportive... 

ADRENAL MEDULLA HORMONES. Adrenaline (epinephrine) and its immediate biological precursor noradrenaline (norepinephrine, levartei-nol) are the principal hormones of the adult adrenal medulla. See Fig.l. Some of the physiological effects produced by adrenaline arc contraction of the dilator muscle of the pupil of the eye (mydriasis), relaxation of the smooth muscle of the bronchi constriction of most small blood vessels dilation of some blood vessels, notably those in skeletal muscle increase in heart rate and force of ventricular conlraction relaxation of the smooth muscle of the intestinal tract and either contraction or relaxation, or both, of uterine smooth muscle. Electrical stimulation of appropriate sympathetic (adrenergic) nerves can produce all the aforementioned effects with exception of vasodilation in skeletal muscle. 

Many of the adrenergic agents produce a transient, incomplete mydriasis when applied to the eye. Cycloplegia does not occur. Ephedrine sulfate in a 3% concentration has been used for this purpose. As has been indicated, the effect is most positive in Caucasians with light-colored irides. Ephedrine is not considered to be a good mydriatic, as it is none too reliable and its solutions are quite irritating to the cornea. Phenylephrine should probably be the adrenergic mydriatic of choice. 

Sympathomimetic agents, such as brimonidine tartrate, apraclonidine, adrenaline and dipivefrine hydrochloride, which is a prodrug for adrenaline), act on a-adrenoreceptors to induce dilation of the veins to reduce IOP. They also induce mydriasis (dilation of the pupils). Adrenaline may reduce the rate of formation of the aqueous humour, which in turn reduces the IOP it may also increase the outflow through the trabecular meshwork. Stimulation of alpha-2-adrenoreceptor (c -adrenoreceptor) by drugs such as brimonidine and apraclonidine on the adrenergic neurons supplying the ciliary body can also result in reduction of secretion of aqueous humour. 

Topical instillation of a 1% solution in eyes with normal adrenergic innervation causes mydriasis and also some vasoconstriction. However, hydroxyamphetamine is used only as a mydriatic agent. After topical application onset occurs within 15 minutes, maximum dilation occurs within 60 minutes, and the duration of mydriasis is approximately 6 hours. The U.S. Food and Drug Administration has labeled this drug as a Pregnancy Category C. 

The ocular effects of cocaine include anesthesia (see Chapter 6), mydriasis, and vasoconstriction. The mydriatic effect of cocaine depends on the presence of a functioning adrenergic innervation. After topical appUcation to the eye, the pupil begins to dilate within 15 to 20 minutes. The maximum effect, which is typically less than 2 mm of dilation, occurs within 40 to 60 minutes, and the pupil may remain dilated for 6 or more hours. The mydriasis is accompanied by vasoconstriction that causes blanching of the conjunctiva. Cocaine is also readily absorbed through the mucous membranes into the systemic circulation. 

Adverse reactions with antihistamines are the result of multiple mechanisms (see Figure 13-3). Muscarinic, a-adrenergic, and serotonin receptor blockade may result in mydriasis, dry mouth and eyes, urinary retention, constipation, and dizziness in first-generation antihistamines. When the neurotransmitter effect of histamine is interrupted, various CNS adverse reactions may occur. These side effects include increased sedation, decreased cognitive function, decreased psychomotor function, and headache. 

The goal of dilation should be wide and rapid mydriasis. The use of a combination of adrenergic and anticholinergic agents achieves this goal.The single instillation of tropicamide or phenylephrine alone may allow some... 

Dapiprazole HCl (Rev-Eyes) is an a-adrenergic blocking agent introduced for the treatment of iatrogenically induced mydriasis. One of the side effects of this topical agent is ptosis. In theory, this effect could potentially be useful for early eyelid retraction of Graves disease. Other side effects, however, include burning on instillation and moderate to severe conjimctival injection. There has been no published study about the efficacy of dapiprazole to relieve eyelid retraction in class 1 disease. 

Ataxia, seizures, psychosis, coma, mucous membrane irritation, bloody diarrhea Delirium, seizures, hypotension, cardiac arrest Mydriasis, dizziness, respiratory arrest Tonic-clonic spasms, coma, hypotension, cardiac arrest Headache, muscle spasms, coma, respiratory arrest Vertigo, seizures, respiratory arrest, hypotension, cardiac arrest Dizziness, mydriasis, seizures, bradycardia, muscle paralysis, respiratory arrest Mydriasis, anxiety, tremor, fx-1 adrenergic block with hypertension, cardiac arrest... 

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