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11.1 Administration of Drugs to the Eye



Various preservatives are used in multidose eyedrops. These are often a source of hypersensitivity reactions. Allergy to the preservative should be considered if a patient's condition worsens on treatment.

Soft contact lenses

Preparations containing benzalkonium chloride are unsuitable as it is concentrated within the lens, then leaches out and irritates the conjunctiva.

Chlorhexidine acetate is suitable in some cases.

Phenylmercuric acetate nitrate is usually satisfactory but is not recommended for long-term use.

Thiomersal is usually satisfactory.


The conjunctival sac can accommodate volumes of between 7 and 30 microlitres. Volumes in excess of this can be systemically absorbed (see below). It is important to instil one drop at a time. If two or more sets of eyedrops are to be administered at the same time, dilution and overflow can occur. Between 3 and 5 minutes should be left between applications to minimise this effect.

Systemic absorption

This can occur with all eye drops but is particularly significant for betablockers and atropine Patients should be instructed to apply pressure over the lachrymal sac for 1 minute after instillation.

Ophthalmic Specials Guidance

The Royal College of Ophthalmologists