Pupillary dilation , agents

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). 

Pharmacology Epinephrine, a direct-acting sympathomimetic agent, acts on and receptors. Topical application, therefore, causes conjunctival decongestion (vasoconstriction), transient mydriasis (pupillary dilation), and reduction in intraocular pressure (lOP). It is believed lOP reduction primarily is caused by reduced aqueous production and increased aqueous outflow. The duration of decrease in lOP is 12 to 24 hours. 

Thyroid Disease. Elevated blood pressure or other adverse cardiovascular effects can result when patients with Graves disease receive adrenergic agonists with vasopressor activity. This is due to the increased catecholamine activity associated with hyperthyroidism. The primary agent to be avoided or used cautiously is topically applied phenylephrine for pupillary dilation. 

Another study compared the mydriatic effect of 2.5% phenylephrine to 1% hydroxyamphetamine in a group of 28 young adult subjects without ocular disease. The two agents produced a nearly equal pupillary dilation (Figure 8-3). The maximum effect with both drugs occurred at approximately 45 minutes. 

Despite the reduction in pupil size, however, dapiprazole may have only limited usefulness in the pre-presbyopic population, because the drug may induce tittle improvement in functional vision as measured by changes in accommodation and near visual acuity. The effect seems to depend on the type of agent used for pupillary dilation. 

The synthetic adrenergic agonists—phenylephrine, naphazoline, oxymetazoline, and tetrahydrozoline—are available as ocular decongestants (Table 13-2). After topical application to the eye, constriction of conjimcti-val blood vessels occurs at drug concentration levels that generally do not cause pupillary dilation. These agents provide only palliative therapy, because they have no effect on the conjimctival response to antigen. 

Broad-spectrum antibiotic drops, such as 0.3% tobramycin, 0.3% ciprofloxacin, or the newer generation fluoroquinolones, moxifloxacin or gatifloxacin, may be instilled four times daily to prevent secondary infection as the epithelium heals. A broad-spectrum ophthalmic ointment, such as 0.3% ciprofloxacin, may be instilled into the conjunctival sac at bedtime for prophylaxis. In more pronounced cases, pupillary dilation and cyclo-plegia with a long-acting agent such as 5% homatropine may help to relieve pain from associated ciliary spasm. 

Jimson weed is a form of Datura that can have relatively high concentrations of antimuscarinic agents and therefore is considered to be certain to cause pupillary dilation. 

Systemic antimuscarinic agents, including atropine and scopolamine, can be administered in doses that could produce mild dilation of the pupil and accommodative paresis.The degree of mydriasis and decreased pupillary reactivity to light provide a clinical measure of antimuscarinic activity. Other commonly used systemic medications with antimuscarinic activity are the Hi receptor antagonists. 

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. 

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