Human transscleral albumin permeability and the effect of topographical location and donor age

To quantify the permeability coefficient of albumin across human sclera and to assess topographical and age-related variation.

Equatorial superotemporal scleral tissue from 15 donor eyes (mean age 60 years; range 39-84) was mounted in a modified Ussing chamber. Additional tissue was taken from the anterior and posterior superotemporal regions of six eyes, and equatorial superonasal, and inferotemporal regions of a further six eyes. Fluorescein isothiocyanate (FITC)-labeled, 0.412 mM, bovine albumin was placed in one hemichamber facing the internal scleral surface, and the rate of transscleral flux was determined over 24 hours, at 25 degrees C, with a spectrophotometer.

Permeability coefficient for equatorial superotemporal scleral tissue at 25 degrees C (+/-SD) was 0.83 +/- 0.50 x 10(-6) cm . s(-1). The permeability coefficient adjusted for 37 degrees C (+/-SD) was 1.43 +/- 0.86 x 10(-6) cm . s(-1). The effect of donor age was assessed for the 15 equatorial superotemporal samples. Regression analysis showed a significant decline in scleral diffusion of albumin with increasing donor age (P = 0.0166). There was no significant difference in diffusion over the different topographical regions tested. The partition coefficient of permeability to albumin also showed a decline with increasing donor age (P = 0.001).

The permeability and partition coefficients of human sclera both significantly decline with increasing donor age. Permeability coefficient shows no significant variation over the different topographical regions tested. The decrease in albumin permeability with increasing donor age may have pharmacokinetic implications when considering transscleral diffusion of high-molecular-weight compounds.