Atropine pupillary effects

Lowering of pupillary sphincter tonus and pupillary dilation by local administration of homatropine or tropic-amide (mydriatics) allows observation of the ocular fundus. For diagnostic uses, only short-term pupillary dilation is needed. The effect of both agents subsides quickly in comparison with that of atropine (duration of several days). 

Muscarinic cholinomimetics mediate contraction of the circular pupillary constrictor muscle and of the ciliary muscle. Contraction of the pupillary constrictor muscle causes miosis, a reduction in pupil size. Miosis is usually present in patients exposed to large systemic or small topical doses of cholinomimetics, especially organophosphate cholinesterase inhibitors. Ciliary muscle contraction causes accommodation of focus for near vision. Marked contraction of the ciliary muscle, which often occurs with cholinesterase inhibitor intoxication, is called cyclospasm. Ciliary muscle contraction also puts tension on the trabecular meshwork, opening its pores and facilitating outflow of the aqueous humor into the canal of Schlemm. Increased outflow reduces intraocular pressure, a very useful result in patients with glaucoma. All of these effects are prevented or reversed by muscarinic blocking drugs such as atropine. 

B. The deadly nightshade of middle Europe (Atropa belladonna, a solanaceous herb)1 contains the alkaloids atropine, in all its parts, and scopolamine, in smaller amounts. The effects of this drug were already known in antiquity e. g., pupillary... 

Tropicamide is an anticholinergic drug that tends to have a greater mydriatic than cycloplegic effect. It is a short-acting atropine-like derivative and has been regarded as an effective and safe mydriatic, used for pupillary dilatation by professionals, who are not always medical doctors. 

Phenylephrine is a sympathomimetic aj adrenoceptor agonist capable of producing mydriasis in some species by iris dilator muscle contraction. In the horse, topical application of a 10% solution has been shown to have no effect on the pupil diameter in the normal eye. However, 10% phenylephrine in combination with topical atropine is reported to be useful in reversing pupillary spasm in some stubborn cases of anterior uveitis, although there is no pharmacological evidence to support any additive mydriatic effect when the two agents are used together. 

Atropinic drugs dilate the pupil (mydriasis) and paralyse accommodation (cycloplegia). Locally applied, atropine or scopolamine produce ocular effects of considerable duration accommodation and pupillary reflexes may not be fully recovered for 7 to 12 days. However when applied as a mydriatic, scopolamine acts faster than atropine but for a shorter time. 

The simplest synthetic mydriatic of the series is phenylisopropylamine or benzedrine (C6H6CH2CH(CH3)NH2) a 1 % solution, instilled into the conjunctival sac, causes complete pupillary dilatation within an hour, the effect wearing off in about 2 hours. Paredrine (4-HOC6H4CH2CII(CH3)-NH2) is even more effective and is probably the most effective synthetic mydriatic of the sympathomimetic drugs. It causes no significant increase in intraocular pressure and can be safely combined with atropine or hom-atropine if paralysis of accommodation is also required. 

Pupillary dilation, not constriction, is a characteristic atropine effect, as indicated by the origin of the name belladonna ( beautiful lady ) from the ancient cosmetic use of extracts of the At-ropa belladonna plant to dilate the pupils. The answer is (B). 

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