Schlemm's canal and the collector channels at different developmental stages in the human eye.

We studied Schlemm's canal (SC) and other posttrabecular structures of aqueous humor outflow in eyes from human fetuses (at 24, 26, 33 and 36 weeks of gestation), eyes from normal children (2 months and 8 years old) and normal adult eyes, using mesoscopy/diaphanization and light microscopy. This study points to the presence of a collector canal parallel to the outer wall of SC (the outer collector). At 24 weeks of gestation, the SC was observable throughout the entire circumference (360 degrees) and the anlage of the outer collector was present. At 26 weeks of gestation, the outer collector was still growing. At 33 weeks of gestation, the outer collector was parallel to the SC and had become visible in some sectors. At 36 weeks, the SC and the outer collector were clearly defined and connected by intercanal links. The intrascleral plexus was growing. At 2 months, the deep intrascleral plexus and the episcleral plexus continued to grow, developing by sectors. At 8 years of age, the same structures corresponded to those in adults. The outer collector and the intrascleral plexuses were divided into sectors not greater than 120 degrees.