Willekens B, Vrensen G
Tissue Cell. 1985;17(3):359-77. doi: 10.1016/0040-8166(85)90055-2.
The three-dimensional organization of the eye lenses of the chicken, the canary, the song-thrush and the kestrel was studied using light and scanning electron microscopy. The lenses of birds are characterized by the presence of two distinct compartments: the annular pad and the main lens body, separated by a cavum lenticuli. The annular pad fibers had a hexagonal circumference all contained a round nucleus and except for the canary were smooth-surfaced and lacking anchoring devices. In the canary, however, the annular pad fibers were studded with edge protrusions and ball-and-socket junctions. The semicircular main lens body fibers of all four species were studded with ball-and-socket junctions and edge protrusions. In contrast with mammals these anchoring devices were present throughout the lens up to the embryonal nucleus. Superficially the main lens body fibers were extremely flat. Additionally membrane elevations and depressions and globular elements were found on these central fibers in three species, the kestrel being the exception. At the transition between annular pad and main lens body the fibers turned their course and the nuclei became oval and disappeared in the deeper aspect of the main lens body. The cavum lenticuli was filled with globules tied off from the annular pad fibers. It seems attractive to assume that the presence of a separated annular pad, a cavum lenticuli filled with globular elements, the extreme flatness of the superficial central fibers and the studding of these central fibers with anchoring devices up to the embryonal nucleus are morphological expressions of the mouldability of the bird's eye lenses and consequently would explain their efficient accommodative mechanism including formation of a lenticonus. The presence of nuclei in the annular pad fibers and their typical change at the transitional zone between annular pad and main lens body are suggestive for a two-phased differentiation in bird's lens fibers: differentiation of the germinative epithelial cells to annular pad fibers which migrate to the main lens body after which they differentiate further to main lens body fibers.
利用光学显微镜和扫描电子显微镜对鸡、金丝雀、歌鸫和红隼的眼球晶状体的三维结构进行了研究。鸟类的晶状体具有两个不同的部分：环形垫和主要晶状体主体，由晶状体腔隔开。环形垫纤维的周长呈六边形，都含有一个圆形细胞核，除金丝雀外，其表面光滑且没有固定装置。然而，在金丝雀中，环形垫纤维上布满了边缘突起和球窝连接。所有这四个物种的半圆形主要晶状体主体纤维上都布满了球窝连接和边缘突起。与哺乳动物不同的是，这些固定装置在整个晶状体中都存在，一直到胚胎核。从表面上看，主要晶状体主体纤维极其扁平。此外，在三个物种的这些中央纤维上还发现了膜状隆起、凹陷和球状结构，红隼除外。在环形垫和主要晶状体主体之间的过渡处，纤维改变了方向，细胞核变成椭圆形，并在主要晶状体主体的较深处消失。晶状体腔充满了从环形垫纤维上分离出来的小球。可以推测，分离的环形垫、充满球状结构的晶状体腔、表面中央纤维的极度扁平以及这些中央纤维上直至胚胎核的固定装置的存在，是鸟类眼球晶状体可塑性的形态学表现，因此可以解释它们高效的调节机制，包括晶状体圆锥的形成。环形垫纤维中细胞核的存在以及它们在环形垫和主要晶状体主体之间过渡区的典型变化，提示鸟类晶状体纤维存在两阶段分化：生发上皮细胞分化为环形垫纤维，后者迁移到主要晶状体主体，然后进一步分化为主要晶状体主体纤维。
