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J. R. Kuszak, M. Mazurkiewicz, R. K. Zoltoski; A Dynamic Demonstration of the Anatomical Basis for Variable Human Lens Shape Change to Effect Accommodation Throughout Life. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4029. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The slit-lamp biomicroscope, a low resolution instrument, shows in situ that different age-related regions of the human lens (fetal, infantile, juvenile and adult nuclei as well as age-matched cortical region) undergo variable gross shape changes to effect accommodation throughout life. The purpose of this study was to create an animation showing the anatomical basis at the fiber cell level for the above described slit-lamp observations.
Chemical fixation was used to ‘stop motion’ in human lenses (n = 40+) in the accommodated and disaccommodated states at different ages (12 - 80+). Lenses were then dissected in a manner permitting ex vivo analysis with a scanning electron microscope, a high resolution instrument, of different aged fiber cells as they had more or less efficiently accommodated throughout life. From the SEM micrographs scale CAD drawings were then used to restore the dynamics of accommodation throughout life in an accelerated time lapse CAD movie.
Throughout gestation fibers are formed that do not develop fiber ends capable of interfacing at the sutures to effect accommodation. However these fibers are pliable and therefore throughout infancy as the anterior ends of infantile cortical fiber cells interface at sutures, the shape of the fetal nucleus is altered. By young adulthood, alterations in the surface morphology of the fetal and infantile nuclear fibers (development of furrowed membrane domains necessary for long-term survival of lens fibers) precludes any significant shape change in these regions to effect accommodation. For the rest of life, the change in surface curvature of the lens to effect accommodation is a function of the number of growth shells that consist of cortical fiber cells capable of interfacing at sutures to enable dynamic focusing balanced against the number of growth shells that consist of nuclear fiber cells rendered incapable of interfacing at sutures due to the above described age-related surface modifications of fibers.
Fibers formed before sexual maturation are involved in the accommodative process by either actively interfacing at lens sutures or passively being compressed in response to the above action. Fibers past sexual maturation are rendered incapable of participating in the accommodative process due to the necessity of developing age-related modifications in their structure to ensure their long-term survival. The animations highlight how previously unrecognized alterations in fiber cell morphology can affect accommodation.
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