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We have used an improved protocol to prepare human, human neonatal, rat and frog lenses for examination by stereo scanning electron microscopy. In this manner, complete and accurate images of the changes in lens cell shape, size and surface complexity are revealed as they differentiate and develop from cuboidal epithelial cells into elongate fiber cells. This method also shows that the apical ends of elongating fibers are variably expanded as they interface with the overlying lens epithelium. Apical ends are most expanded as they contact pre-germinative zone epithelial cells and least enlarged as they contact transitional zone cells. By examining the interlocking devices on opposed fibers in frog, rat and human lenses we determined that there are standard types and interlocking patterns in all lens species. Finally, stereo SEM reveals that the ridges previously reported on aged human nuclear fibers are also seen on human neonatal cortical fibers and that these ridges may actually be interlocked villous or fingerlike projections.

The sutures of the crystalline lens have previously been studied by light microscopy (LM). While the gross suture patterns (umbilical, line, y-shaped and star) of lenses are readily visualized by LM, fiber cell shape, curvature, length and the morphology of fiber cell ends cannot be adequately resolved by this technique. We have used scanning electron microscopy (SEM) to examine the sutures of crystalline lenses. SEM has revealed that in lenses with line, y-shaped or umbilical sutures, the anterior and posterior ends of fiber cells curve away in opposite directions from the polar axis of the lens before interlocking at suture branches. The degree of curvature decreases as a function of the number of suture branches. This relationship was not resolved by LM. SEM has revealed that the relationship of fiber cell taper to suture type was underestimated by previous LM studies. The reduction in fiber cell width from the equator to the sutures is 3:1 and 2:1 respectively, in lenses with line and y-shaped sutures. Furthermore, in lenses with star sutures, fiber cells are flared (1:1.7) rather than tapered, a fact not reported by previous LM studies. SEM also revealed that the offsetting of anterior and posterior suture branches does not result in equal fiber cell length in any growth ring as reported by LM studies. Rather, fiber cell length in any one growth ring varies as a sine wave function according to fiber cell location at the equator. Furthermore, the range of fiber cell length decreases as a function of the number of suture branches. Finally, SEM has revealed that the distal ends of fiber cells are expanded in both width and thickness prior to interlocking at suture branches and that these ends overlap rather than simply abut end-to-end to form a three dimensional suture plane extending down from the lens surfaces to the primary fiber cell mass.