Computer modeling of secondary fiber development and growth: I.Nonprimate lenses

[摘要] Purpose: The purpose of this study was to use qualitative andquantitative structural data from nonprimate lenses with branched (Y andline) sutures to generate computer models (animations) of secondaryfiber development and suture formation.Methods: A minimum of 12-18 adult lenses/species (mice, cows, frogs,and rabbits) were used in this study. Lenses were analyzed by light(LM), transmission (TEM), and scanning electron microscopy (SEM). Fiberwidth, thickness, and length were ascertained from micrographs and byusing formulations to calculate distances between degrees of latitudeand longitude on asymmetrical oblate spheroids. This information wasthen used to create scale computer assisted drawings (CADs) of fibers atdifferent stages of their development. The CADs were then placed on atimeline and animated to produce dynamic representations of secondaryfiber development and growth.Results: Animating secondary fiber development and suture formationwith the inclusion of quantifiable differences in fiber dimensions atprogressive stages of their differentiation revealed the following:first, there is the presumption that fibers migrate, rotate, andelongate until they reach their sutural destinations is not likely to becorrect. When developing fibers reach approximatelty 60-65% of theireventual total length, their migration and rotation is complete. Theremaining fiber elongation (the production of end segments) occurswithout either concomitant cellular migration or rotation. Second, it ispresumed that suture branches originate peripherally and are thenconstructed sequentially until all of the branches come to confluence atthe poles is also not likely to be correct. While suture branches dooriginate peripherally, if the rate of elongation is constant in theanterior and posterior directions (intrafiber elongation speed) andbetween developing fibers within a forming growth shell (interfiberelongation speed), then only a part of their construction proceedssequentially toward the poles. A second suture branch origin will beestablished at the poles resulting in a short distal portion of suturebranches being formed sequentially in the reverse direction. Sutureformation will conclude when a long proximal and a short distal portionof branches come to confluence within unequal anterior and posteriorpolar cap regions. This segmented suture formation scheme will be morepronounced in line suture lenses than in Y suture lenses. Third, becauselenses with branched sutures have growth shells consisting of fibers ofunequal length, fiber maturation is likely to be initiated in theselenses before a growth shell as well as suture formation is completedand would proceed in distinct patterns over a period of time. This is inmarked contrast to avian lens fiber maturation which does not beginuntil growth shell and suture (branchless umbilical) formation iscompleted and then occurs rapidly and essentially simultaneously acrossthe entire growth shell.Conclusions: Animations of secondary fiber development and sutureformation based on quantitative analysis of electron micrographs revealsimportant novel aspects of these processes that have not been apparentfrom the results of previous mechanistic studies. The more complexschemes of fiber differentiation and suture formation presented hereinare consistent with the notion that lens function (dynamic focusing) isinterdependent on lens structure and physiology. The animations confirmthat while all vertebrate lenses have a similar structure, differencesin the level of their structural complexity established early indevelopment and maintained throughout life can account for the varyingamount of optical quality known to exist between species.

[学科分类] 生物化学/生物物理