Prescribing for and Administration of Drugs to the Eye

There are several methods of achieving therapeutic drug concentrations within the eye and its surrounding structures. By far the most common is topical administration but when higher concentrations of the drug are required, local injection or systemic administration is considered. Prescription and/or administration of the latter is most commonly initiated in the Eye Clinic, with the exception of a few conditions e.g. suspected cases of giant cell arteritis.

Eye drops

• Instil in lower conjunctival fornix and ideally keep eye closed for 1-2 minutes after application.
• Only one drop is needed per dose - excess drops are quickly washed away at rate proportional to amount instilled.
• Principally absorbed through cornea but absorption through conjunctival mucosa also occurs, giving rise to systemic effects.
• High intraocular concentrations achieved if applied regularly.¹
• Drops may be in solution form (clear, e.g. anaesthetic drops) or in suspension (cloudy, e.g. steroids). Suspensions can settle therefore advise a gentle shake of the bottle before applying.
• There is a short drug-eye contact time so they tend to need a more frequent application.

Eye ointments

• Apply a small amount of ointment the in lower conjunctival fornix and blink to help spread over cornea. Wipe excess clean before subsequent application.
• May cause blurring initially: this will resolve as ointment melts away.
• Ointments allow a prolonged contact time therefore less frequent applications are required (good for night use).
• Help lubrication so concurrent lubricant use not always necessary (unless there was previous intensive usage or there is a large abrasion).

Eye lotions

These are solutions used for irrigation of conjunctival sac (to flush out particles and chemical irritants). Sterile normal saline is the norm but clean water will do in an emergency.

Systemic absorption of topical drugs

• Occurs more readily with drops than ointment; absorption occurs via conjunctival vessels.
• Can be limited to some degree by compressing medial punctum and nasolacrimal sac on drop application ("press your finger firmly over your lids, next to the nose").
• The fellow eye may be affected by systemic absorption of the drug applied to the treated eye.¹
• A common culprit is β blockers - check risk factors.
• Usual rules regarding pregnant and breast feeding patients apply.

Multiple drug treatment

• If the patient needs more than one drop, allow 4-5 minutes between each drop.
• If there is a mixture of drops and ointments: instil drop first and then ointment after 4-5 minutes.
• Topical and systemic treatment: check for duplication (e.g. beta-blockers) and drug interactions (e.g. carbonic anhydrase inhibitors) and (loop diuretics).

Avoiding microbial contamination

• Use single application packs in surgery clinic/emergency department (e.g. fluorescein drops).
• Wash hands before and after application; this is particularly important if you suspect or are treating infective eye disease.
• Discard bottles 28 days after opening.

"Drop allergy" - preservative toxicity

A wide variety of preservatives are used in ophthalmic topical medication to keep it sterile. These may be toxic to the precorneal tear film and about 10% of patients also experience a hypersensitivity reaction to the preservatives, notably to the most commonly used one: benzalkonium chloride.¹ They may experience redness, itching, burning, blurring of vision and in more severe cases, punctuate keratitis (tiny spots of fluorescein uptake on cornea) or corneal oedema (cornea goes hazy). The patient often clearly relates symptoms with starting the drops. Change to single dose drops: minims (they come in little individual plastic vials that can only be used once). Check with ophthalmology team if doubt over link between drops and symptoms and signs.

Topical drugs and contact lens wear²

• If treatment is initiated in the community, it is essential that you are happy that you are not treating a contact lens induced corneal ulcer: this needs specialist treatment and monitoring.
• Remove lens when instilling drops.
• Avoid soft lens wear with drops unless preservative-free; hard lens wear acceptable.
• Ointments are not compatible with contact lens wear.

Common difficulties in topical administration

• Drop instillation can be tricky ("I can't touch my eyes Doc", elderly patient with rheumatic hands): consider ointment alternative or drop dispenser (handed out by pharmaceutical companies for their individual product: talk to the dispensing chemist). Dispensers are re-usable.
• Ointment can be messy or awkward and can give rise to contact dermatitis:¹ wipe excess away after application or consider drops.

Local injections: what to expect

If a patient is told that they will have an "injection in the eye" (such as the local anaesthetic before cataract surgery or steroid treatment in severe uveitis), they will experience the following:

• An anaesthetic drop will be administered
• A small spring will be applied to hold the lids open (painless)
• A small incision is made in the conjunctiva: they should not feel it.
• They will probably feel the agent being infiltrated in: the subtenon approach is favoured (Tenon's fascia is a tough fibrous coat around the globe) - the needle does not penetrate the globe
• The spring is removed and a pad is placed over the eye
• Discomfort / pain varies between individuals and depends on what is being injected
• Patients will commonly have a red eye or may have a small subconjunctival haemorrhage after: this should begin to resolve over 24-48 hours

Systemic treatment for ophthalmic problems

Physiological barriers limit systemically administered drug penetration to the eye although this improves in inflamed states. More common examples include antibiotics for orbital cellulitis, steroids for giant cell arteritis and acetazolamide for severely raised intraocular pressure. Another important area of systemic drug prescription for ophthalmic problems is to control pain e.g. following a corneal abrasion. Topical local anaesthetics are not recommended (other than at the point of initial assessment); oral paracetamols and NSAIDs are suitable choices in these patients.

Systemic treatment for systemic problems: effect on the eye

Ocular side effects from systemic drugs, such as cataract formation from prolonged systemic steroid use, can occur. Other examples are listed below:^2,3

• Amiodarone: corneal deposits
• Anticonvulsants: ocular motility dysfunction
• Atropine: pupillary dilation
• Digoxin: abnormalities of colour vision
• Ethambutol, quinine: optic neuropathy
• Hydroxychloroquine, chloroquine: retinal changes and corneal deposits
• Isosorbide dinitrate: transient myopia
• Opiates: pupillary constriction
• Phenothiazines: retinal changes and ocular motility dysfunction
• Sulphonamides and NSAIDs: Stevens-Johnson syndrome
• Tamoxifen: retinal changes

A number of drugs interfere with contact lens wear including the oral contraceptive pill, aspirin, drugs affecting blink rate and drugs affecting lacrimation. See our records on Contact Lenses and Contact Lens-related Problems for more information.

There are a number of commonly used over the counter preparations, examples of which include:

• Antihistamines e.g. Otrivine-Antistin®
• Antimicrobials e.g. Brolene®, Golden Eye Ointment® (both fine with soft contact lens wear), chloramphenicol antibiotic drops
• Artificial tears e.g. Viscotears®, Lacri-lube® (both fine with soft contact lens wear)
• Astringents e.g. Eye Dew Clear®, Optrex Fresh Eyes®
• Mast cell stabilisers e.g. Opticrom allergy eye drops®