Eye Drops: Route of Administration
Eye drops are administered via the topical route of administration in pharmacology. 1
Definition and Classification
Topical ophthalmic administration involves the instillation of drops or ointments directly to the ocular surface. 1 This is classified as a trans-topical delivery method, which is distinct from:
- Intravitreal injection (direct injection into the posterior segment) 1
- Systemic administration (oral or intravenous routes that cross the blood-retinal barrier) 1
Key Characteristics of Topical Eye Drop Administration
Advantages
- Most convenient and patient-compliant route for treating anterior segment diseases 2
- Non-invasive and accessible to all patients 3
- Provides rapid and localized drug action 4
- The eye's partial exposure to the external environment enables this topical approach 1
Limitations
- Bioavailability is typically less than 5% from conventional eye drops 4
- Less than 5% of topically applied drugs reach the anterior chamber 1
- For posterior segment delivery, less than 1/108 of topically administered protein drugs reach retinal targets 1
Clinical Context
The FDA labels timolol ophthalmic solution as "FOR TOPICAL APPLICATION IN THE EYE", confirming the topical route designation. 5 The American Academy of Ophthalmology consistently refers to glaucoma medications as topical therapy requiring proper instillation technique. 1, 6
Important Clinical Distinction
While eye drops use the topical route, this differs fundamentally from intravenous administration, where standard IV sets deliver 20 drops per milliliter (approximately 50 microliters per drop). 7 Ophthalmic drops have different volume characteristics and are applied to the ocular surface rather than systemically.