Sutures of the crystalline lens: a review

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.