Sensory Neurobiology Group, Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2012 Dec;198(12):849-56. doi: 10.1007/s00359-012-0755-9. Epub 2012 Sep 16.
The cornea is the first optical element in the path of light entering the eye, playing a role in image formation and protection. Corneas of vertebrate simple camera-type eyes possess microprojections on the outer surface in the form of microridges, microvilli, and microplicae. Corneas of invertebrates, which have simple or compound eyes, or both, may be featureless or may possess microprojections in the form of nipples. It was previously unknown whether cephalopods (invertebrates with camera-type eyes like vertebrates) possess corneal microprojections and, if so, of what form. Using scanning electron microscopy, we examined corneas of a range of cephalopods and discovered nipple-like microprojections in all species. In some species, nipples were like those described on arthropod compound eyes, with a regular hexagonal arrangement and sizes ranging from 75 to 103 nm in diameter. In others, nipples were nodule shaped and irregularly distributed. Although terrestrial invertebrate nipples create an antireflective surface that may play a role in camouflage, no such optical function can be assigned to cephalopod nipples due to refractive index similarities of corneas and water. Their function may be to increase surface-area-to-volume ratio of corneal epithelial cells to increase nutrient, gas, and metabolite exchange, and/or stabilize the corneal mucous layer, as proposed for corneal microprojections of vertebrates.
角膜是光线进入眼睛的第一个光学元件，在成像和保护方面发挥着作用。脊椎动物简单相机型眼睛的角膜在外表面具有微突起，形式为微脊、微纤毛和微褶。具有简单或复眼或两者兼有的无脊椎动物的角膜可能没有特征，也可能具有乳头形式的微突起。以前不知道头足类动物（具有与脊椎动物相似的相机型眼睛的无脊椎动物）是否具有角膜微突起，如果有，其形式如何。我们使用扫描电子显微镜检查了一系列头足类动物的角膜，发现所有物种都存在乳头样微突起。在一些物种中，乳头类似于节肢动物复眼上描述的乳头，具有规则的六边形排列，直径从 75 到 103nm 不等。在其他物种中，乳头呈结节状且分布不规则。尽管陆地无脊椎动物的乳头会产生抗反射表面，这可能在伪装中发挥作用，但由于角膜和水的折射率相似，不能将这种光学功能赋予头足类动物的乳头。它们的功能可能是增加角膜上皮细胞的表面积与体积比，以增加营养、气体和代谢物的交换，和/或稳定角膜粘液层，正如对脊椎动物角膜微突起所提出的那样。
