Medications,Pharmacology: What are examples of mydriatics?

October 10, 2025 •

4 min read

According to the American Optometric Association, a dilated eye exam is a standard part of a comprehensive eye and vision examination for adults to properly evaluate the internal structures of the eye. What are examples of mydriatics, the medications that make this procedure possible by causing pupils to dilate? These agents are crucial for both diagnostic and therapeutic purposes in eye care.

Quick Summary

Mydriatics are medications used to dilate the pupil, with examples including anticholinergic agents such as tropicamide and sympathomimetic agents like phenylephrine. These eye drops are used in diagnostic procedures and for treating certain eye conditions like uveitis.

Key Points

Anticholinergics vs. Sympathomimetics: Mydriatics are categorized into anticholinergics (e.g., tropicamide) that block pupil constriction and sympathomimetics (e.g., phenylephrine) that stimulate pupil dilation.
Tropicamide is the shortest-acting mydriatic: It is frequently used for routine eye exams due to its rapid onset and short duration of action (4–8 hours).
Atropine has the longest duration: As the most potent and long-lasting mydriatic, its effects can persist for 7–14 days, making it suitable for therapeutic uses like treating uveitis.
Many mydriatics also cause cycloplegia: Anticholinergic mydriatics often paralyze the focusing muscle of the eye, a side effect called cycloplegia, which causes temporary blurry near vision.
Side effects include light sensitivity and blurred vision: Patients who receive mydriatic drops are advised to wear sunglasses and avoid driving or operating machinery until their vision has returned to normal.
Mydriatics are essential for comprehensive eye exams: These medications provide ophthalmologists with a clear view of the retina and other internal eye structures for diagnostic purposes, such as screening for diabetic retinopathy.
Combination drops offer synergistic effects: Products like Cyclomydril combine different classes of mydriatics (e.g., cyclopentolate and phenylephrine) for enhanced dilation.

Introduction to Mydriatic Agents

Mydriatic agents are a class of medications that cause mydriasis, or pupil dilation, by affecting the muscles of the iris. This is an essential process for ophthalmologists and optometrists to conduct thorough eye examinations, especially for viewing the retina and other posterior structures. Beyond diagnostics, these agents also serve therapeutic purposes, such as treating certain inflammatory conditions and managing amblyopia. The different types of mydriatics achieve their effect through distinct pharmacological mechanisms, primarily by interacting with the autonomic nervous system that controls pupil size. Understanding these differences helps in selecting the appropriate agent for a specific clinical need, considering factors like onset of action, duration, and potential side effects.

Classifications of Mydriatics

Mydriatics are broadly categorized based on their primary mechanism of action. The two main classes are anticholinergics and sympathomimetics, which respectively block the constricting muscle or stimulate the dilating muscle of the iris.

Anticholinergic (Parasympatholytic) Mydriatics

This group of medications works by blocking the neurotransmitter acetylcholine from binding to its muscarinic receptors on the iris sphincter muscle. By inhibiting the parasympathetic pathway, these agents relax the sphincter, leading to pupil dilation. A key feature of these drugs is that most also cause cycloplegia, or paralysis of the ciliary muscle, which results in a temporary inability to focus on near objects.

Atropine: A potent and long-acting mydriatic, atropine’s effects can last up to 7–14 days. Due to its extended duration, it is not typically used for routine diagnostic purposes but is valuable for therapeutic uses, such as treating uveitis or amblyopia in children.
Cyclopentolate: This agent offers a rapid onset (30–60 minutes) and an intermediate duration of action (6–24 hours), making it a popular choice for clinical refraction, particularly in pediatric patients.
Tropicamide: Known for its fast onset (20–40 minutes) and short duration (4–8 hours), tropicamide is the drug of choice for routine diagnostic dilation when a quick recovery is desired.
Homatropine: With a potency and duration between atropine and cyclopentolate, homatropine is effective for treating anterior uveitis by relieving ciliary muscle spasm and preventing the formation of adhesions.

Sympathomimetic (Adrenergic Agonist) Mydriatics

These drugs work by stimulating the sympathetic pathway, specifically targeting the alpha-1 adrenergic receptors located on the iris dilator muscle. This causes the dilator muscle to contract, pulling the pupil open. An advantage of sympathomimetics is that they produce mydriasis with minimal or no cycloplegia, which avoids the associated blurred near vision.

Phenylephrine: As a pure mydriatic, phenylephrine is commonly used in combination with anticholinergic agents to achieve maximum dilation, especially in individuals with dark irides. It has a rapid onset and lasts for a few hours. However, the 10% solution can cause cardiovascular side effects and is used with caution.

Comparison of Common Mydriatics


Feature	Tropicamide	Phenylephrine	Atropine	Cyclopentolate
Drug Class	Anticholinergic	Sympathomimetic	Anticholinergic	Anticholinergic
Mechanism	Blocks muscarinic receptors	Stimulates alpha-1 adrenergic receptors	Blocks muscarinic receptors	Blocks muscarinic receptors
Primary Effect	Mydriasis & mild cycloplegia	Pure mydriasis	Mydriasis & strong cycloplegia	Mydriasis & moderate cycloplegia
Onset of Action	Fast (20–40 minutes)	Rapid (15–60 minutes)	Slower (30–40 minutes)	Rapid (30–60 minutes)
Duration of Action	Short (4–8 hours)	Moderate (3–6 hours)	Long (7–14 days)	Moderate (6–24 hours)
Primary Use	Routine diagnostic exams	Combination for maximal dilation	Therapeutic treatment, amblyopia	Clinical refraction, pediatric use

Uses and Patient Considerations

Beyond basic dilation for diagnostic exams, mydriatics are used in specific clinical situations. For example, in managing anterior uveitis, atropine or homatropine helps prevent the iris from adhering to the lens, a condition known as posterior synechiae. In pediatric ophthalmology, cycloplegics are often combined with mydriatics to paralyze the eye's focusing muscles, allowing for an accurate measurement of refractive error. Combination drops, such as the fixed-combination product MydCombi (phenylephrine and tropicamide), are also available to achieve a synergistic effect.

Patients using mydriatic drops are advised of several common side effects, including light sensitivity (photophobia) and blurry vision. To manage these, patients are often advised to wear sunglasses after the drops are administered and avoid driving or other hazardous activities until their vision returns to normal. Ophthalmic professionals also take precautions in patients with pre-existing conditions like narrow-angle glaucoma, as dilation can potentially trigger an acute attack. Other side effects can include stinging, headaches, and in rare cases, systemic issues like increased heart rate or blood pressure, particularly with the higher concentration of phenylephrine.

Conclusion

Mydriatics are a cornerstone of modern ophthalmology, enabling detailed examinations and effective treatment of various eye conditions. From the rapid-acting tropicamide used for routine check-ups to the potent, long-lasting atropine for therapeutic management, a variety of agents are available to suit different clinical needs. The two primary pharmacological classes, anticholinergics and sympathomimetics, achieve pupil dilation through distinct mechanisms and offer unique profiles regarding onset, duration, and effects on accommodation. Patient safety is prioritized through careful selection of the agent and proactive management of side effects like light sensitivity. As technology advances, novel drug delivery systems are also emerging to further optimize the administration and efficacy of these important ophthalmic medications.

Frequently Asked Questions

Mydriatics are agents that cause pupil dilation, or mydriasis. Cycloplegics paralyze the ciliary muscle, inhibiting accommodation (the eye's ability to focus on near objects). Many anticholinergic mydriatics also have cycloplegic effects.

The duration depends on the specific agent used. Fast-acting drops like tropicamide wear off in 4–8 hours. Intermediate-acting drops like cyclopentolate last 6–24 hours, while potent ones like atropine can last for days.

No, it is not recommended. Mydriatic drops can cause blurred vision and increased sensitivity to light (photophobia), which can impair driving ability. Patients should wait until their pupils have returned to normal before driving.

Yes, mydriatic drops can cause a temporary increase in intraocular pressure, particularly in individuals with narrow-angle glaucoma. Eye care professionals take precautions and often avoid these drops in such cases.

In addition to diagnostic exams, mydriatics are used to treat conditions like anterior uveitis, where they prevent painful ciliary spasm and formation of posterior synechiae (adhesions). Some are also used to manage amblyopia in children.

Yes, combination products like Cyclomydril, which contains both cyclopentolate and phenylephrine, are used to achieve synergistic effects for more robust pupil dilation.

Patients with darker irises may require higher concentrations or more doses of mydriatic agents to achieve adequate dilation. This is because iris pigment can absorb the medication, reducing its effect on the pupillary muscles.