Gustafsson Ola S E, Ekström Peter, Kröger Ronald H H
Department of Biology, Lund University, Zoology Building, Helgonavägen 3, 223 62 Lund, Sweden.
J Morphol. 2010 Aug;271(8):980-9. doi: 10.1002/jmor.10849.
The sharpness and thus information content of the retinal image in the eye depends on the optical quality of the lens and its accurate positioning in the eye. Multifocal lenses create well-focused color images and are present in the eyes of all vertebrate groups studied to date (mammals, reptiles including birds, amphibians, and ray-finned fishes) and occur even in lampreys, i.e., the most basal vertebrates with well-developed eyes. Results from photoretinoscopy obtained in this study indicate that the Dipnoi (lungfishes), i.e., the closest piscine relatives to tetrapods, also possess multifocal lenses. Suspension of the lens is complex and sophisticated in teleosts (bony fishes) and tetrapods. We studied lens suspension using light and electron microscopy in one species of lamprey (Lampetra fluviatilis) and two species of African lungfish (Protopterus aethiopicus aethiopicus and Protopterus annectens annectens). A fibrous and highly transparent membrane suspends the lens in both of these phylogenetically widely separated vertebrate groups. The membrane attaches to the lens approximately along the lens equator, from where it extends to the ora retinalis. The material forming the membrane is similar in ultrastructure to microfibrils in the zonule fibers of tetrapods. The membrane, possibly in conjunction with the cornea, iris, and vitreous body, seems suitable for keeping the lens in the correct position for well-focused imaging. Suspension of the lens by a multitude of zonule fibers in tetrapods may have evolved from a suspensory membrane similar to that in extant African lungfishes, a structure that seems to have appeared first in the lamprey-like ancestors of allextant vertebrates.
眼睛中视网膜图像的清晰度以及由此产生的信息含量取决于晶状体的光学质量及其在眼中的精确位置。多焦点晶状体能产生聚焦良好的彩色图像，并且在迄今为止研究的所有脊椎动物类群（哺乳动物、包括鸟类的爬行动物、两栖动物和硬骨鱼）的眼睛中都存在，甚至在七鳃鳗中也有，七鳃鳗是眼睛发育良好的最原始脊椎动物。本研究中通过视网膜检影法获得的结果表明，肺鱼目（肺鱼），即与四足动物亲缘关系最近的鱼类，也拥有多焦点晶状体。硬骨鱼（硬骨鱼类）和四足动物中晶状体的悬韧带复杂而精巧。我们使用光学显微镜和电子显微镜研究了一种七鳃鳗（河七鳃鳗）以及两种非洲肺鱼（非洲肺鱼指名亚种和非洲肺鱼相近亚种）的晶状体悬韧带。在这两个系统发育上相距甚远的脊椎动物类群中，一种纤维状且高度透明的膜将晶状体悬吊起来。该膜大约沿着晶状体赤道附着于晶状体，从那里延伸至视网膜锯齿缘。构成该膜的物质在超微结构上与四足动物小带纤维中的微原纤维相似。该膜可能与角膜、虹膜和玻璃体协同作用，似乎适合将晶状体保持在正确位置以实现聚焦良好的成像。四足动物中由众多小带纤维悬吊晶状体的方式可能是从类似于现存非洲肺鱼的悬韧带膜进化而来的，这种结构似乎最早出现在所有现存脊椎动物的七鳃鳗样祖先中。
