A new theory states that mechanical rubbing between anterior packets of zonules and the peripheral iris in predisposed eyes is the cause of the loss of iris pigment in pigmentary glaucoma and in the pigmentary dispersion syndrome. The peripheral radial defects were in close approximation to anterior packets. The total number of iris defects in advanced cases correlated with the average number of anterior packets. Histologic study showed a groove in the stroma of the iris as well as loss of the pigmented neuroepithelium and was compatible with mechanical damage. The theory explains why the disease predominates in young myopic men, why it decreases in incidence with age, and why, in some cases, it regresses. Treatment with an alpha-adrenergic blocking agent may be advantageous in this condition.