Recent studies have sought to quantify aqueous flare by laser flare measurement. An increase in aqueous flare caused by a rise of protein concentration was frequently found both in anterior and posterior segment disease. This has been interpreted as a break-down of the blood--aqueous barrier (BAB). By measuring the diffusion coefficient of the BAB compared to the aqueous flare value in patients with anterior and posterior uveitis, the extent to which the increase in flare value was related to a possible break down of the BAB was examined.
Patients: Thirty-nine normal eyes (23-78 years; 41.6 +/- 18.6), 18 eyes with anterior uveitis (iritis, iridocyclitis; 18-57 years; 35.2 +/- 12.4) and 29 eyes with posterior uveitis (chorioretinitis or retinochorioditis; 18-51 years; 31.7 +/- 10.5). The diffusion coefficient P(a) of the BAB was measured fluorophotometrically, while the flare value was quantified by laser flare measurement.
Results: Flare values (1/ms) were found to be significantly increased (p < 0.001) compared to normal eyes (4.6 +/- 1.7) both in anterior uveitis (20.9 +/- 8.5) and in posterior uveitis (17.4 +/- 8.3) but did not significantly differ between them (p = 0.43). The diffusion coefficient P(a) (10(-3)/min) of the BAB was not significantly different (p > 0.05) between normal eyes (0.5 +/- 0.2) and eyes with posterior uveitis (0.9 +/- 0.7), whereas it was significantly increased (p < 0.001) in anterior uveitis (6.5 +/- 5.4) compared to the other groups.
Conclusions: (1) In posterior uveitis, an increased flare value is not necessarily correlated with a breakdown of the BAB; proteins may enter the aqueous from posterior. (2) Assessing the function of the BAB in posterior segment disease using laser measurement should be carried out with caution; if possible, permeability measurements of the BAB should be undertaken separately.