Postnatal evolution of the ciliary processes in the gerbil (Meriones unguiculatus): a structural, ultrastructural and morphometric study

The postnatal evolution of the ciliary processes in the Mongolian gerbil (Meriones unguiculatus) was examined, with particular regard to their morphological organization and to the structural and ultrastructural differentiation of both inner and outer epithelial layers. Gerbil eyes at postnatal (P) 3, 9, 12, 15, 18, 21, and 26 days and at 6 months were fixed with glutaraldehyde 2.5% and examined with the light microscopy on semithin sections and with the transmission electron microscopy. Masked histologists evaluated the samples and performed a morphometric exam on ciliary processes and epithelial cells layers height using the ANOVA test for comparison among groups. From P3 to P15, ciliary processes were formed by rectilinear folds, which progressively elongated at their free extremities. From P18, the processes branched dichotomously and reached their adult zig-zag appearance in cross section at P26. Inner epithelial cells were at first arranged on many layers, then on two layers and, from P15, on a single layer. Outer cells were arranged on a single row from P3. Both cell types showed linear contacts with occasional interdigitations till P9, then complex intercellular junctions. The morphometric analysis demonstrated that while epithelial folds elongated, the ciliary epithelium, and particularly the inner cells, reduced its height. The ciliary processes development of gerbil starts in utero, undergoes significant morphological changes soon after eyelid opening and is completed at P26, when adult organization is reached.