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 notable exception of systemic steroids in suspected cases of giant cell arteritis.

Eye drops

• Instil in lower conjunctival fornix; ideally keep eye closed for 1-2 minutes after application
• Only one drop needed per dose: 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
• 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.
• Short drug-eye contact time so tend to have more frequent application.

Eye ointments

• Apply small amount of ointment in lower conjunctival fornix and blink to help spread over cornea. Wipe excess clean before subsequent application.
• May cause initial blurring: will resolve as ointment melts away
• Prolonged contact time therefore less frequent applications required (good for night use)
• Helps lubrication so concurrent lubricant use not always necessary (unless previous intensive use or large abrasion).

Eye lotions

• Solutions used for irrigation of conjunctival sac (flush out particles and chemical irritants)
• Sterile normal saline 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 ("put 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
• Common culprit: ( β blockers) - check risk factors
• Usual rules regarding pregnant and breast feeding patients apply.

Multiple drug treatment

• More than one drop: allow 4-5 minutes between each drop
• 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: emphasise if suspecting or 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 fluoroscein 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 wear ²

• If treatment initiated in community, make sure 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 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). 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 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.

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
• Hydroxychloroquinine, chloroquinine: retinal changes and corneal deposits
• Isosorbide dinitrate: transient myopia
• Opiates: papillary 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.

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: suitable for minor infections.
• 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®.