• A recently introduced theory of the mechanism of the pigment dispersion syndrome is that pigment granules are released by mechanical contact between the anterior surface of zonular fibrils and the posterior surface of the pigment epithelium of the iris. A photogrammetric study of the depth of the central and peripheral anterior chamber of the iris was carried out in 37 subjects with the pigment dispersion syndrome. These subjects had deeper anterior chambers, particularly in the midperiphery, than could be accounted for by their age, sex, or refractive error. Excessive depth of the anterior chamber is demonstrated to be a risk factor in the pigment dispersion syndrome. Concavity of the midperipheral iris surface was demonstrated in this group of subjects, confirming previous clinical observations and giving additional support to the mechanical theory of pigment dispersion.