Mandeep Brar

Introduction

A patient on the ward with heart block is prescribed timolol eye drops. Another patient taking oral acetazolamide develops paraesthesia and is found to have worsening renal function. Later that week, you are asked to prescribe antibiotic drops for a red eye. How confident are you that you know what to prescribe – and what to look out for?

Ophthalmic medications are frequently encountered by doctors outside ophthalmology, particularly in inpatient and emergency department settings. Although many are administered topically, they can have significant systemic effects, contraindications and adverse effects that are important for junior doctors to recognise. This practical guide highlights commonly encountered ophthalmic medications and the key prescribing considerations that every junior doctor should know (1,2,3).

Learning Objectives

Recognise commonly encountered ophthalmic medications and their principal indications.

Identify important ocular and systemic contraindications and cautions.

Recognise situations in which ophthalmic medications may cause significant systemic effects.

Recognise when prescribing an ophthalmic medication should prompt urgent specialist assessment or advice.

A simple approach to ophthalmic medications

1  What is it for?

2  When shouldn’t I use it?

3  What can it do to the patient?

4  When do I need help?

It’s only an eye drop…” – systemic effects

Clinical Scenario

68-year-old with glaucoma, asthma and pulse 52. Regular medication: timolol.

What is your concern?

Key Fact

Eye drops can have systemic effects (3, 4,5,12)

Timolol is a non-selective β-adrenergic receptor blocker that works on β₁ and β₂ receptors on the ciliary body of the eye to reduce production of aqueous humour and as such lower intraocular pressure. It is often used to treat patients with glaucoma. Despite being a topical medication, it can be systemically absorbed. For this reason it is contraindicated in conditions such as reactive airway disease/asthma, severe COPD, bradycardia, heart block or conduction disease, overt cardiac failure and cardiogenic shock (3, 4).

Similarly,

Brimonidine is a α₂-adrenergic receptor agonist working to activate the α₂ receptors in the ciliary body to reduce production of of aqueous humour and increases uveoscleral outflow. These actions lower intraocular pressure and for this reason it is used as topical eye drop to treat glaucoma. The useful prescribing point is that brimonidine can be systemically absorbed despite being a topical eye drop. Its systemic adverse effects include drowsiness, fatigue, hypotension, bradycardia, dizziness and dry mouth. (3, 5)

The steroid trap

Clinical Scenario

A 28-year-old presents with a painful, photophobic, red eye and reduced vision. They have been using dexamethasone eye drops prescribed by another clinician.

What is your concern?

Steroid eye drops often seen prescribed include prednisolone 1% preparations such as Predsol and Pred Forte, and dexamethasone 0.1% (Maxidex). The main mechanism of this medication is to bind to intracellular glucocorticoid receptors, reduce inflammatory mediator production and suppress inflammatory cell activity. Steroid eye drops are commonly prescribed by specialists for anterior uveitis, postoperative inflammation, allergic conjunctivitis and iritis. Steroids do not treat the underlying cause of inflammation; they suppress the inflammatory response (3, 6,7).

This becomes particularly important when infection is a possibility. Corticosteroids can impair corneal healing and suppress the local immune response, potentially worsening or masking infection. Contact lens wear is an important risk factor for microbial keratitis. Always ask your patient if they wear contact lenses, and if they do, consider infection as a differential (3, 6,7,8).

When should you seek specialist advice?

Consider if the patient has pain, photophobia or reduced vision – which can mean corneal involvement – or do they wear contact lenses? If so, consider microbial keratitis and seek ophthalmology advice before prescribing steroid drops (8).

Key Point

An undifferentiated red eye is not an indication for empirical topical steroids (3, 6,7,8).

Dangers Of Steroid Eye Drops

The most important ocular adverse effects of topical steroids is they raise intraocular pressure (IOP). With prolonged use there can also be cataract formation. Steroids can cause or exacerbate ocular hypertension and may worsen IOP control in patients with glaucoma (3, 6,7).

Key Point

Don’t start or stop steroids yourself. Like any form of steroids, it will require a tapering dose (3, 6,7).

Glaucoma medications: what do you actually need to know?

Clinical Scenario

A 72-year-old patient is started on oral acetazolamide by ophthalmology for raised intraocular pressure. They have chronic kidney disease and develop nausea, fatigue and tingling in their hands.

What should a junior doctor be aware of?

Acetazolamide works by systemically inhibiting carbonic anhydrase. In the eye it reduces the flow of sodium and fluid into the posterior chamber that makes the aqueous humour production. Acetazolamide tablets are thus used to reduce IOP in acute angle closure glaucoma. However, it has systemic implications, causing paraesthesia, electrolyte disturbances and metabolic acidosis (3, 9,10).

Acute angle closure: what can be used if acetazolamide is poorly tolerated?

This is where as a junior doctor you should seek specialist opinion. If your patient has poor renal function or is having side effects from acetazolamide, there are alternative pathways for managing acute angle closure glaucoma (9,10).

Before you dilate: mydriatics and cycloplegics

Clinical Scenario

A 72-year-old has a painful red eye, blurred vision, headache and nausea. You are asked to administer dilating drops.

Should you proceed?

It is important to recognise the possibility of acute angle closure in this patient. Painful red eye, blurred vision, headache and nausea are classic features that should raise suspicion. 10,8

Mydriatics

Mydriatics include tropicamide and phenylephrine. Tropicamide is a muscarinic receptor antagonist that relaxes the iris sphincter muscle, causing the pupil to dilate. Phenylephrine is a selective α₁-adrenergic receptor agonist that contracts the iris dilator muscle, producing mydriasis. They are often used together to achieve adequate pupil dilation for fundal examination (3,11,12).

Cycloplegics

Cycloplegics include cyclopentolate and atropine. They are antimuscarinic drugs that block parasympathetic stimulation of the ciliary muscle, producing cycloplegia (paralysis of accommodation) and mydriasis. They are commonly used in children for cycloplegic refraction. In anterior uveitis, cycloplegics such as atropine can reduce painful ciliary muscle spasm and prevent posterior synechiae (3,13).

Both groups of dilating drops can precipitate acute angle closure in patients with narrow or occludable angles, particularly in those with a shallow anterior chamber (10,11,12,13).

Key Fact

Do not routinely dilate a patient with a painful red eye, blurred vision, headache or nausea. Urgent ophthalmic assessment and IOP measurement are required if acute angle closure is suspected (8,10).

Clinical Scenario

A patient with significant cardiovascular disease is due to receive phenylephrine for pupil dilation.

Is phenylephrine purely a local medication?

Answer

No (3,12).

Phenylephrine is a topical eye drop that can result in systemic absorption and has a risk of hypertension, tachycardia, arrhythmias, palpitations and headaches. Caution is required in patients with significant cardiovascular disease and hypertension (3,12).

Antibiotics: when is a red eye actually an infection?

Clinical Scenario

A 32-year-old presents with a unilateral red eye, watery discharge and mild discomfort. They have no pain, photophobia or visual loss. They ask for chloramphenicol because they have previously been given it for a “sticky eye”.

What should you consider before prescribing?

With a red eye, a number of differentials should come to mind. It is not always due to infection. Viral, allergic and uncomplicated bacterial conjunctivitis are often self-limiting and may not require antibiotic treatment. If bacterial conjunctivitis is suspected, chloramphenicol is commonly used as a first-line topical antibiotic. Other antibiotics broader-spectrum/fluoroquinolone treatment may be used in specific circumstances (3,14,8).

When should you seek specialist advice?

Consider ophthalmology assessment if the patient wears contact lenses, has a history of ocular foreign body, develops pain, photophobia or visual loss, or has persistent or worsening symptoms despite appropriate initial treatment (8).

DANGERS OF ANTIBIOTICS

Chloramphenicol is contraindicated in patients with a history of serious blood dyscrasias or previous chloramphenicol-associated bone marrow suppression (3,14).

“Don’t prescribe this for pain”

Clinical Scenario

A patient with a corneal abrasion has excellent pain relief after topical anaesthetic and asks to take the drops home.

Should you prescribe them?

Topical ocular anaesthetics, including tetracaine and lidocaine, block voltage-gated sodium channels in sensory nerve fibres, preventing transmission of pain signals from the cornea and conjunctiva. They are primarily used to provide short-term anaesthesia during ophthalmic procedures, including foreign body removal, corneal sampling/swabbing, Goldmann applanation tonometry and ocular surgery (3,15).

The cornea has one of the highest densities of sensory nerve endings in the body, supplied predominantly by the ophthalmic division of the trigeminal nerve (CN V1). This contributes to the significant pain experienced with corneal abrasions and ulcers (3).

Danger Of Tetracaine Eye Drops

Topical anaesthetics are not suitable for ongoing analgesia. By reducing corneal sensation, they can diminish protective blinking and reflex lacrimation and mask ongoing corneal injury. Repeated or prolonged use can also cause corneal epithelial toxicity, delayed healing and potentially progressing to corneal ulceration, melting and perforation (3,15).

FY2 Ophthalmic Prescribing Checklist

Follow this checklist to assist you when you encounter any eye drop.

Before prescribing an ophthalmic medication, ask: (1,2,3)

• What is it for? Is there a clear diagnosis and indication?
• Is it safe for this patient? Check contraindications, comorbidities, allergies and interactions.
• What can it do systemically? Remember: topical does not always mean local.
• Does dose or duration matter? Consider renal function, duration and maximum doses.
• Could I make this patient’s eye worse? Be particularly cautious with steroids, anaesthetics and an undifferentiated red eye.

Does this patient need ophthalmology input?  Consider pain, photophobia, reduced vision, corneal involvement, contact lenses, trauma/foreign body or deterioration despite treatment.

When in doubt, check the BNF/local guidance and seek advice from your ophthalmology team (1,2,3,8).

References

1. Royal College of Ophthalmologists. PM3: Use of drugs. RCOphth Curriculum. [date unknown].

2. Royal College of Ophthalmologists. BCS8: Clinical therapeutics. RCOphth Curriculum. [date unknown].

3. Joint Formulary Committee. British National Formulary (BNF). London: BMJ Group and Pharmaceutical Press; 2026.

4. Timolol 0.5% eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2020.

5. Brimonidine tartrate 2 mg/mL eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2025.

6. Pred Forte 1% w/v eye drops suspension. Summary of Product Characteristics. Electronic Medicines Compendium; 2024.

7. Maxidex 0.1% w/v eye drops suspension. Summary of Product Characteristics. Electronic Medicines Compendium; 2026.

8. National Institute for Health and Care Excellence. Red eye. NICE Clinical Knowledge Summaries. [date unknown].

9. Acetazolamide 250 mg tablets. Summary of Product Characteristics. Electronic Medicines Compendium; 2025.

10. Royal College of Ophthalmologists. The management of angle-closure glaucoma. London: Royal College of Ophthalmologists; 2022.

11. Tropicamide 1% w/v eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2026.

12. Phenylephrine hydrochloride 2.5% eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2025.

13. Cyclopentolate hydrochloride 0.5%/1% eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2024.

14. Chloramphenicol 0.5% w/v eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2024.

15. Tetracaine hydrochloride 1% eye drops. Summary of Product Characteristics. Electronic Medicines Compendium; 2015.