Changes in the surface morphology of lens fibres in the developing chick eye in relation to lens transparency

The surface morphology of chick lens fibres and epithelium was studied by scanning electron microscopy at several stages of embryonic development. In common with many species of adult lens, the embryonic fibres possessed a remarkable array of interlocking devices which were present from an early stage of development. The primary and secondary fibres both acquired projections during the maturation process, although the types of interlocking devices were different in the two populations. Immediately after obliteration of the lens vesicle, 'flap' or 'finger-like' projections were seen on the primary fibres, and these increased in number during development. A pronounced change in the morphology of the primary fibres was seen between Stages 35 and 38 with the formation of large irregular, interlocking processes. Secondary fibre maturation resulted in a complex but well defined joining apparatus with 'mounds and hollows', 'finger', 'flap' and 'ball-like' projections being formed. Transmission electron microscope grids placed beneath the lenses allowed a direct assessment of lens transparency during development. In the early stages, the lens appeared opaque, uniform transparency becoming apparent between 6-7.5 days of incubation. No specific correlations between the morphology of the lens fibres and the degree of transparency were found, although the size of extracellular spaces appeared to be important, close packing of fibres being generally associated with transparency.