Shun-Shin G A, Vrensen G F, Brown N P, Willekens B, Smeets M H, Bron A J
Clinical Cataract Research Unit, Nuffield Laboratory of Ophthalmology, Oxford, England.
Invest Ophthalmol Vis Sci. 1993 Dec;34(13):3489-96.
Christmas tree cataract consists of highly refractile multicolored "needles" crisscrossing the lens fibers of the deep cortex. The fact that the colors vary according to the angle of the incident light, and that in retroillumination only a dim outline of the cataract is seen, would suggest that Christmas tree cataract is a diffractive phenomenon. This study was performed to unravel the ultrastructure and chemical composition of the Christmas tree needles.
Eight lenses from donor eyes and four extracapsularly extracted lenses with Christmas tree cataract were investigated by scanning and transmission electron microscopy. The chemical composition was studied with energy-dispersive x-ray microanalysis and Raman microspectroscopy.
Scanning electron microscope examination showed that the needles are smooth, rectangular, plate-like elements bordered by membranes and amorphous material and running crisscross through the lens. In the specimens for transmission electron microscopic examination, the needles proved to be largely dissolved, but the remains showed regular spacings of approximately 5 nm. Material identical in spacing and electron density was found in neighboring cells bound to a reticular membranous network originating from the fiber-limiting membranes. Energy-dispersive x-ray and Raman microanalysis showed that the needles have a high sulfur content and pronounced S-S, CS-SC, and C-S vibrations. The cytoplasm adjacent to the needles and reticular meshwork had an elevated Ca++ content.
It is concluded that cystine is the most likely candidate for the Christmas tree needles and that the needles probably are formed as the result of an age-related aberrant breakdown of crystallins induced by elevated Ca++ levels.
圣诞树状白内障由高度折射的多色“针状物”组成，这些针状物纵横交错于深层皮质的晶状体纤维中。颜色会根据入射光的角度而变化，并且在视网膜反光检查中只能看到白内障的模糊轮廓，这表明圣诞树状白内障是一种衍射现象。本研究旨在揭示圣诞树状针状物的超微结构和化学成分。
对来自供体眼的8个晶状体以及4个患有圣诞树状白内障且经囊外摘除的晶状体进行扫描电子显微镜和透射电子显微镜检查。采用能量色散X射线微分析和拉曼显微光谱法研究其化学成分。
扫描电子显微镜检查显示，针状物是光滑的、矩形的、板状结构，边缘有膜和无定形物质，纵横交错贯穿晶状体。在用于透射电子显微镜检查的标本中，针状物大部分已溶解，但残留部分显示出约5纳米的规则间距。在与源自纤维限制膜的网状膜网络相连的相邻细胞中，发现了间距和电子密度相同的物质。能量色散X射线和拉曼微分析表明，针状物含有高硫含量以及明显的S-S、CS-SC和C-S振动。与针状物和网状网络相邻的细胞质中Ca++含量升高。
得出的结论是，胱氨酸最有可能是圣诞树状针状物的成分，并且这些针状物可能是由Ca++水平升高导致的与年龄相关的晶状体蛋白异常分解形成的。
