Ocuserts are thin, flexible, polymeric devices shaped to fit in the conjunctival sac and designed to release a drug at a slow, controlled rate for a prolonged period.
They represent a unique amalgamation of the principles of both pharmacology and polymer science to achieve controlled drug delivery to the eye.
Classification of Ocuserts:
1. Based on Physical State:
A. Soluble ocuserts:
These are made from materials that dissolve over time in the tear fluid, releasing the drug as they dissolve.
The entire ocusert eventually dissolves, so there's no need to remove it.
The dissolution rate of the polymer determines the drug release rate.
B. Insoluble ocuserts:
Made from non-dissolvable materials, these ocuserts release their drug over time but remain intact.
After they've expended their drug content, they need to be removed from the eye.
2. Based on Drug Release Mechanism:
A. Reservoir systems:
These have a separate compartment or layer for the drug, which is then surrounded by a rate-controlling membrane.
The drug diffuses out of the reservoir through the membrane at a controlled rate.
The membrane's permeability and thickness determine the drug's release rate.
B. Matrix systems:
The drug is uniformly distributed within a polymer matrix.
Drug release happens as the drug diffuses out from the matrix.
The release rate can be controlled by altering the matrix's composition and the drug's dispersion within the matrix.
3. Based on Location of Application:
A. Conjunctival ocuserts:
These are designed to fit snugly in the conjunctival sac, ensuring prolonged contact with the ocular surface.
B. Corneal ocuserts:
These are smaller and designed to be placed directly on the cornea.
Given the sensitive nature of the cornea, these are less common and require precise design considerations to ensure comfort and safety.
4. Based on Duration of Action:
A. Short-term ocuserts:
Designed for a drug release spanning a few hours to a day.
These can be beneficial for post-surgical drug delivery or acute conditions.
B. Long-term ocuserts:
These are crafted to release the drug over extended periods, ranging from several days to weeks.
Such ocuserts are especially useful for chronic conditions like glaucoma.
5. Based on Biodegradability:
A. Biodegradable ocuserts:
Made from materials that break down over time into harmless components, eliminating the need for removal from the eye after the drug is delivered.
B. non-biodegradable ocuserts:
Crafted from materials that don't degrade in the ocular environment.
These need to be removed after their drug content is exhausted.
Composition of ocuserts
1. Drug Reservoir:
The core part that holds the drug. It usually contains a suitable polymeric matrix in which the drug is dispersed or dissolved.
2. Rate-controlling Membrane:
This surrounds the drug reservoir and regulates the rate at which the drug is released. The membrane is usually impermeable to the drug, so the drug release occurs through specially designed pores or through diffusion.
3. Back Layer:
Typically impermeable, it ensures that drug release is unidirectional (towards the eye).
