The present invention relates to a method of increasing the bioavailability and/or prolonging ophthalmic action of a drug, the method comprising instilling into the eye an aqueous suspension comprising reversible clusters of drug loaded nano-resin particles, said clusters having a D50 value of at least 2 micrometer and said drug loaded nano-resin particles have a particle size distribution characterized in that the D90 value is 70 nanometer to 900 nanometer. The present invention further relates to an aqueous suspension comprising reversible clusters of drug loaded nano-resin particles, said clusters have a D50 value of at least 2 micrometers and said drug loaded nano-resin particles have a particle size distribution characterized in that the D90 value is 70 nanometers to 900 nanometers.