Liposomes: 1- It shows improved efficacy and stability of the drug. 2- It facilitates the transport of drugs across ocular corneas from unilamillar liposomes as it serve as carrier vehicle Ex: inulin absorption is increased ten-fold when topically applied in a liposome carrier.

Ophthalmic Inserts: Lacrisert:  A sterile, translucent, rod-shaped, water-soluble [solid hydrophilic ocular inserts] form of hydroxy-propyl cellulose.  The insert acts to stabilize and thicken the precorneal tear film and to delay its breakup, it is used once or twice daily,  The inserts soft and slowly dissolved following administration.

Ocusert (Alza)  The insert is oval with dimensions of 13.4 by 5.7 mm and 0.3 mm in thickness.  It is flexible and is a multilayered structure consisting of a drug containing core surrounded on each side by layer of copolymer membranes through which the drug diffuses at a constant rate.

 The rate of drug diffusion is controlled by the polymer composition, the membrane thickness and the solubility of the drug.  Inserts containing pilocarpine are widely used to release medication over a 7-days period at which time they are removed and replaced with new ones.

Contact Lenses

Major Characteristics Chemical Classification Lens Type Negligible gas permeability, low water content, medium wettability PMMA(polymethylmethacrylate) Hard rigid, hydrophobic low gas permeability, High water content, good wettability HEMA (hydroxyethyl methylmethacrylate)Soft-flexible,hydrophilic Good gas permeability Poor wettability Silicone rubber Flexible hydrophobic Good gas permeability Good wettability Silicone vinylpyrollidone Good gas permeability Good wettability CAB (cellulose acetate butyrate) Rigid hydrophilic

Soft contact lenses: Advantages Hydropilic transparent polymer of HEMA contains up to 80% water which improve lense permeability to oxygen.

Disadvantages They are capable of absorbing some topically administered drugs thereby affecting the drug bioavailability. Some ophthalmic suspensions may build up between lens and the eye lens interface causing undesired effects and discomfort. Provides a reduction in quality of vision.

Some drugs, administered by various routes of administration for systemic effects may find their way to the lachrymal fluid and produce drug-contact lens interactions, such as: a)Lens discoloration (e.g. orange staining by rifampin), b)Lens clouding (ribavirin), c)Ocular inflammation (salicylates), d)Refractive changes (acetazolamide).

Hard contact lenses: Disadvantages  They are made of a rigid plastic resin, PMMA which is uncomfortable to be wear and tolerated by many people.  Impermeable to oxygen and moisture which is a disadvantage to corneal epithelial respiration.  Direct contact of hard lenses on the corneal surface may lead to epithelial tissue damage. To prevent this effect, solutions are used that wet the surface of the lens to provide wetting layer between the corneal epithelium and the inner surface of the lens.

It has strength and durability and easy care regimens. Easy to handle during insertion and removal. Resist the absorption of disinfectants, surfactant cleansers, and environmental contaminants. Provide visual acuity superior to soft contact lenses. Rigid Gas Permeable [RGP] Contact Lenses Advantages :

Disadvantages: Hard and require an adjustment period and become dislodged or migrate in the eye.