Reverse pupillary block is introduced as a new cataract-implant complication and as the principle mechanism in pigmentary dispersion syndrome (PDS) and pigmentary glaucoma (PG), causing posterior iris bowing and zonular rubbing. This mechanism was investigated by performing laser iridotomy on six patients. Following surgery, the iris moved forward completely and permanently to the planar position. A new technique, locating the iridotomy by transillumination, reduced the laser energy needed for iridotomy. Laser iridotomy located with transillumination is recommended as the treatment for iris-zonular rubbing in PDS and PG caused by reverse pupillary block.