What is an example of a mydriatic?

October 9, 2025 •

4 min read

According to the American Academy of Ophthalmology, dilating the pupils is a standard part of a comprehensive eye exam for a deeper view of the eye's internal structures. A prime example of a mydriatic used for this purpose is tropicamide, an ophthalmic solution that rapidly induces pupil dilation.

Quick Summary

Mydriatics are drugs that dilate the pupil by affecting the eye's muscles, commonly used for comprehensive eye exams, surgery, and treating eye inflammation. Key examples include tropicamide, phenylephrine, and atropine, which act through different pharmacological pathways to achieve dilation. Effects can include blurred vision and light sensitivity.

Key Points

Tropicamide: A common example of a mydriatic, used for routine eye exams due to its rapid onset and short duration.
Mechanism: Mydriatics function by either blocking parasympathetic signals (anticholinergics like tropicamide and atropine) or activating sympathetic signals (adrenergic agonists like phenylephrine).
Uses: Primary applications include diagnostic eye exams, facilitating surgery like cataract removal, and treating conditions such as uveitis and amblyopia.
Side Effects: Common side effects include blurred vision and sensitivity to bright light (photophobia), while rare systemic effects like increased heart rate can occur.
Mydriasis vs. Cycloplegia: Mydriasis is pupil dilation, while cycloplegia is paralysis of the eye's focusing muscle. Some drugs, like atropine, cause both effects.
Considerations: The choice of mydriatic depends on the clinical purpose, patient age, and potential contraindications like narrow-angle glaucoma.

Mydriatic agents are a class of drugs used to induce mydriasis, the medical term for pupil dilation. By widening the pupil, these medications allow eye care professionals to perform a more thorough examination of the retina, optic nerve, and other structures at the back of the eye. Different mydriatics are chosen based on the desired speed of onset, duration, and whether a cycloplegic (focus-paralyzing) effect is also needed.

An Example of a Mydriatic: Tropicamide

Tropicamide is one of the most frequently used mydriatic agents for routine ophthalmic procedures. As an anticholinergic drug, it works by blocking the cholinergic receptors on the iris sphincter muscle. This causes the muscle to relax, leading to pupil dilation. Tropicamide is favored in clinical settings because it has a rapid onset of action, typically within 15 to 30 minutes, and a relatively short duration, with effects lasting approximately 4 to 8 hours.

Other Common Mydriatic Agents

While tropicamide is a staple, other mydriatics are used for specific clinical situations, each with a distinct mechanism:

Phenylephrine: This sympathomimetic drug is an alpha-adrenergic agonist that directly stimulates the iris dilator muscle to contract, pulling the pupil open. It provides a rapid but weaker mydriatic effect compared to anticholinergics and does not cause cycloplegia. It is often used in combination with other drops for a stronger effect.
Atropine: An older and longer-lasting anticholinergic mydriatic, atropine is a potent cycloplegic as well. Its effects can last for days or even weeks, making it less suitable for routine exams. However, its long duration is beneficial for treating certain conditions, such as reducing pain from uveitis or as a therapy for amblyopia (lazy eye).
Cyclopentolate: Another anticholinergic agent, cyclopentolate offers a balance between tropicamide's speed and atropine's longevity. It has a powerful cycloplegic effect, which is particularly useful for obtaining an accurate refractive measurement in children, as it temporarily paralyzes the eye's focusing muscles.

The Mechanism of Action: Anticholinergics vs. Adrenergic Agonists

The two primary types of mydriatics work by targeting different parts of the autonomic nervous system that control pupil size. The iris contains two muscles: the sphincter pupillae (circular muscle) and the dilator pupillae (radial muscle).

Anticholinergic Agents: These drugs, such as atropine and tropicamide, block the action of acetylcholine, a neurotransmitter of the parasympathetic nervous system. By inhibiting acetylcholine, these agents relax the sphincter pupillae, allowing the dilator muscle to pull the pupil open. Many of these agents also cause cycloplegia by affecting the ciliary muscle.
Adrenergic Agonists: Agents like phenylephrine stimulate the sympathetic nervous system. They mimic norepinephrine, which causes the radial dilator pupillae muscle to contract, widening the pupil.

Medical Uses of Mydriatic Agents

Beyond routine diagnostic procedures, mydriatics have several important clinical applications:

Dilated Fundus Examination: The most common use. Dilation provides a wide view of the back of the eye, helping to detect signs of glaucoma, diabetic retinopathy, macular degeneration, and other diseases.
Cataract Surgery: Mydriatics are crucial for keeping the pupil open during surgery, allowing the surgeon clear access to the lens.
Treatment of Anterior Uveitis: Conditions involving inflammation of the iris and ciliary body are treated with mydriatics, particularly longer-acting ones like atropine. This helps reduce pain and prevents adhesions (synechiae) between the iris and the lens.
Amblyopia (Lazy Eye) Therapy: Low-dose atropine is sometimes used to blur the vision of the stronger eye, forcing the brain to rely on and strengthen the weaker, or "lazy," eye. This is an alternative to traditional patching.

Comparison of Common Mydriatics


Feature	Tropicamide	Atropine	Phenylephrine
Drug Class	Anticholinergic (Parasympatholytic)	Anticholinergic (Parasympatholytic)	Adrenergic Agonist (Sympathomimetic)
Primary Mechanism	Blocks iris sphincter muscle	Blocks iris sphincter and ciliary muscles	Contracts iris dilator muscle
Typical Onset	Rapid (15–30 minutes)	Slow	Rapid (15 minutes)
Duration	Short (4–8 hours)	Long (days to weeks)	Short (4–6 hours)
Cycloplegic Effect	Weak/Minimal	Strong	None
Key Use	Routine dilated eye exams	Therapeutic uses (uveitis, amblyopia)	Adjunct for dilation, diagnostic

Potential Side Effects and Precautions

The most common side effects of mydriatics are blurred vision and heightened sensitivity to bright light (photophobia) due to the enlarged, fixed pupils. Patients are typically advised to wear sunglasses after dilation and to avoid driving until their vision returns to normal. In rare cases, especially with systemic absorption, more serious side effects can occur, such as a rapid heart rate or behavioral changes, particularly in children. Mydriatics should be used with caution in individuals with narrow-angle glaucoma, as they can cause a dangerous increase in intraocular pressure.

Conclusion

Mydriatics are indispensable tools in ophthalmology, with a variety of agents available to meet different clinical needs. The choice of which mydriatic to use depends on factors like the desired duration of dilation, the need for a cycloplegic effect, and the patient's age and health status. Common examples like tropicamide provide a fast, short-acting effect perfect for routine exams, while potent, longer-acting agents such as atropine serve critical therapeutic roles. By understanding the distinct properties of these medications, eye care professionals can safely and effectively use them to diagnose and treat a wide range of eye conditions. More details on pharmacologic dilation can be found on the EyeWiki on Pharmacologic Dilation.

Frequently Asked Questions

A mydriatic causes pupil dilation (mydriasis), while a cycloplegic causes paralysis of the ciliary muscle, which controls the eye's focusing ability (accommodation). Some drugs, like atropine, have both mydriatic and cycloplegic effects.

The duration depends on the specific drug used. For example, the effects of tropicamide typically last 4 to 8 hours, while the effects of atropine can last for days or even weeks.

The most common side effects are temporary blurred vision and increased sensitivity to light (photophobia). Less frequent side effects can include a headache, dry mouth, or stinging upon application.

Due to the blurred vision and light sensitivity caused by mydriatic drops, it is generally unsafe to drive or operate machinery until your vision has returned to normal. You should arrange for transportation after your appointment.

Dilating the pupils allows an eye doctor to get a better, wider view of the internal structures of the eye, such as the retina and optic nerve, to check for signs of disease.

Mydriatics are also used during eye surgery, to treat painful inflammation of the iris and ciliary body (uveitis), and as a therapy for amblyopia (lazy eye).

While atropine is used in specific pediatric cases, such as for amblyopia, it should be used with caution, particularly in young children, as they can be more sensitive to its side effects. Your ophthalmologist will determine the appropriate dosage and monitor for any adverse reactions.