Locket N A
Department of Anatomy, University of Adelaide, South Australia.
Aust N Z J Ophthalmol. 1992 Nov;20(4):281-95. doi: 10.1111/j.1442-9071.1992.tb00740.x.
Deep or convexiclivate foveas occur in some birds, including raptors, some lizards and certain deep-sea fishes. Theories on their function are reviewed. Common to raptor and deep-sea fish foveas is a radial fibre lining, dark staining so probably optically dense, adjacent to the less refractile vitreous. The foveal curvatures and size are remarkably similar in a wide taxonomic and size range of birds and fishes. Ray plotting through traced foveal outlines suggests that sharp images will be formed beneath the centre and shoulders, with the centre image enlarged enough to account for the high acuity of raptors. Deep foveas will also exaggerate eccentricity of off-centre images of a point source, such as deep-sea fishes may meet. Despite similarities in foveal shape, the receptors differ widely between species. Raptors, and notosudid fishes, have short cones. Searsid fishes have long single rods. Howella and Bajacalifornia have multiple bank rods, more in the fovea than the periphery. Those of Howella are shown to be multiple inner-outer segment complexes rather than interrupted single rods. Implications of foveal and receptor features are discussed.
深凹或凸面小凹出现在一些鸟类中，包括猛禽、一些蜥蜴和某些深海鱼类。本文综述了关于它们功能的理论。猛禽和深海鱼类小凹的共同特征是有一层放射状纤维衬里，染色较深，因此可能光学密度较大，与折射性较小的玻璃体相邻。在广泛的鸟类和鱼类分类及大小范围内，小凹的曲率和大小非常相似。通过追踪小凹轮廓进行光线绘图表明，清晰的图像将在中心和肩部下方形成，中心图像放大到足以解释猛禽的高敏锐度。深小凹也会夸大点光源偏心图像的偏心度，比如深海鱼类可能会遇到这种情况。尽管小凹形状相似，但不同物种的感受器差异很大。猛禽和裸胸鳝科鱼类有短视锥细胞。西氏鱼有长的单杆状细胞。霍氏鱼和巴氏鱼有多层杆状细胞，小凹处比周边更多。研究表明，霍氏鱼的杆状细胞是多个内外节复合体，而不是间断的单杆状细胞。本文讨论了小凹和感受器特征的意义。
