2.6. Ex vivo corneal permeation
Corneal permeation characteristics of optimized formulation of tropicamide-loaded carboxymethyl tamarind kernel polysaccharide nanoparticles were comparatively evaluated with the conventional ophthalmic tropicamide (30 mg/mL) solution using isolated goat cornea as a model [18]. Fresh whole goat eyeball was obtained from the local butcher shop immediately after slaughtering and transported to the laboratory in cold normal saline within an hour. Cornea was carefully excised along with 2–4 mm of scleral tissue and finely cleaned and washed till free from proteins with cold normal saline. Isolated cornea was mounted by clamping between the donor and receptor compartments of modified Franz diffusion cell, with endothelial side facing the receptor and epithelial side facing the donor. The receptor compartment contained 11 mL of freshly prepared Ringer bicarbonate solution maintained at 35 ± 0.5 °C under magnetic stirring. Area available for corneal permeation was 0.95 cm2. One milliliter of test formulation was placed in the donor compartment over the cornea. An aliquot of 3 mL of the sample was withdrawn from receptor compartment after 2 h and analyzed for the contents of tropicamide spectrophotometerically at 257 nm. The study was conducted using paired corneas i.e., one cornea of the animal was used for the permeation study of nanosuspension formulation and the contralateral cornea was used for conventional aqueous drug solution. Corneal hydration level was studied by removing the scleral tissue from the cornea at the end of experiment and weighing followed by dehydration by overnight soaking in methanol and drying in an oven at 90 °C and weighing again.