Diffusion of immunoglobulins into rabbit cornea after subconjunctival injection: experimental demonstration and mathematical model.

To determine whether immunoglobulins of the IgG class diffus up to the corneal center after subconjunctival injection, rabbits were injected with fluorescein-isothiocyanate-labeled human IgG. The inoculum diffused from the entire periphery centrepetally towards the corneal center. The progression of the diffusion front slowed down as the distance to the limbus increased. The first increase of fluorescence in the corneal center was observed on day 6. The intensity increased during the following 10 days despite resorption in the corneal periphery due to the flow of IgG from paracentral toward central areas. The diffusion coefficient of 0.003-0.004 cm2/day was calculated by computer simulation using Fickian diffusion equations adapted for corneal geometry. We conclude that after subconjunctival application, IgG diffuses up to the corneal center with a delay of several days and that the penetration speed decreases as the distance to the limbus increases. This kinetics contributes to our understanding of the role of IgG in corneal pathology and may help to design therapeutic schedules for immunotherapy with IgG.