Subconjunctival injection

• Subconjunctival injections are another means of achieving high therapeutic levels of drugs in the cornea, sclera and anterior segment of the orbit.
• This is particularly important in the emergency management of acute infection or inflammation of the orbit.
• Placing injections subconjunctivally bypasses the lipid layers of the bulbar conjunctiva and places the drugs adjacent to the water-permeable sclera, increasing water-soluble drug penetration into the eye.
• Local deposition allows for the leakage and therefore, corneal penetration.

Uses

• To achieve high corneal and intra-ocular levels of drugs for short periods.
• Administration of drugs that penetrate the cornea poorly (antibiotics) or have slow absorption characteristics (corticosteroids).
• When topical medication cannot be administered, or only infrequently.
• Infrequent yarding of an animal is only possible.

Advantages

• Markedly increased penetration of water soluble drugs.
• Short term high concentrations of drugs in cornea and anterior segment.
• Supplement to topical therapy.

Disadvantages

• Local irritation, residues, necrosis and granuloma formation can occur at the site of injection.
• Once injected the drug(s) cannot be removed.
• Temporary pain at site of injection.
• Injection is quite difficult with potential for injury to eye.

Technical problems

• If the animal is not adequately restrained, there is a risk of accidental needle stick injury to the cornea/sclera/orbit Bovine restraint techniques.
• If inappropriate drugs are injected into the subconjunctiva, this could lead to discomfort for the animal (blephrospasm, epiphora and narrowing of the palpebral fissure).

Alternative techniques

• Topical application of ocular drugs.
• Placement of an indwelling lavage drain system to allow for topical ocular drugs to be applied to the surface of the eye.

Time required

Preparation

• 2-5 minutes (to adequately restrain the animal).

Procedure

• Within 1 minute.