Distribution of complement in the sclera.

In the present study, we compared hemolytic activities of C1, C4, C2, C3, C5, C6 and C7 in the anterior and posterior sclera. Additionally, we used radial immunodiffusion to measure levels of Factor B, IgG, IgA and albumin in the anterior and posterior sclera. Except for C1, complement levels were significantly higher in the posterior than anterior sclera. Additionally, levels of immunoglobulins as well as albumin were significantly higher in the posterior than anterior sclera. These results suggest that the posterior sclera has a better adjacent vascular supply than the anterior sclera. On the other hand, the results of this study show that the anterior sclera has more C1, the recognition unit of the classical pathway, than the posterior sclera. Because there is nearly twice as much C1 in the anterior sclera, it may be easier for antigen-antibody complexes, whether formed in the sclera itself or derived from the neighboring vessels, to set off the complement cascade in the anterior sclera. This finding may help explain why scleritis associated with immune complex disease is more common in the anterior than posterior sclera.