Transscleral albumin diffusion and suprachoroidal albumin concentration in uveal effusion syndrome.

Purpose: To test the hypothesis that uveal effusion syndrome is caused by reduced transscleral albumin permeability.

Methods: Surgical scleral specimens were obtained from a 55-year-old patient with nanophthalmic uveal effusion syndrome. Specimens were clamped in a modified Ussing chamber, and the rate of transscleral diffusion of fluorescein isothiocyanate-albumin was measured over 12 hours, using a spectrophotometer and predetermined standard curves. The diffusion coefficient was determined at 20°C, and then adjusted to body temperature using Einstein's equation. Results in 3 scleral samples were compared with 10 age-matched controls. Albumin and total protein concentration were measured in choroidal fluid and serum.

Results: Histologic staining with Alcian blue showed interfibrillary acid mucin deposits. Transmission electron microscopy showed deposits measuring 1 μm to 10 μm and collections of expanded, degenerate collagen fibrils. The mean (±SD) albumin diffusion coefficient was 12% of that in controls (1.22 ± 0.67(-8) × 10 vs. 10.3 ± 7.0 × 10(-8) cm2/second) and below the lower 95% confidence limit of the control group. The diffusion coefficient was calculated to increase 53% to 1.87 ± 1.03 × 10(-8) cm2/second at 37°C. Choroidal albumin concentration was much higher than physiologic levels, measuring 200 g/L (total protein 321 g/L), 5 times the serum albumin concentration of 42 g/L (total protein 70 g/L).

Conclusion: Nanophthalmic uveal effusion syndrome can be associated with reduced scleral permeability to albumin, and a very high concentration of retained suprachoroidal albumin. This will lead to an osmotic gradient that retains fluid and may partly explain the pathogenesis of uveal effusion syndrome in some patients.