Diffusion of Protein through the Human Cornea

Abstract

Aims: To determine the rate of diffusion of myoglobin and bovine serum albumin (BSA) through the human cornea. These small proteins have hydrodynamic diameters of approximately 4.4 and 7.2 nm, and molecular weights of 16.7 and 66 kDa, for myoglobin and BSA, respectively. Meth ods: Diffusion coefficients were measured using a diffusion chamber where the protein of interest and balanced salt solution were in different chambers separated by an ex vivo human cornea. Protein concentrations in the balanced salt solution chamber were measured over time. Diffusion coefficients were calculated using equations derived from Fick’s law and conservation of mass in a closed system. Results: Our experiments demonstrate that the diffusion coefficient of myoglobin is 5.5 ± 0.9 × 10^–8 cm²/s (n = 8; SD = 1.3 × 10^–8 cm²/s; 95% CI: 4.6 × 10^–8 to 6.4 × 10^–8 cm²/s) and the diffusion coefficient of BSA is 3.1 ± 1.0 × 10^–8 cm²/s (n = 8; SD = 1.4 × 10^–8 cm²/s; 95% CI: 2.1 × 10^–8 to 4.1 × 10^–8 cm²/s). Conclusions: Our study suggests that molecules as large as 7.2 nm may be able to passively diffuse through the human cornea. With applications in pharmacotherapy and the development of an artificial cornea, further experiments are warranted to fully understand the limits of human corneal diffusion and its clinical relevance.