The fine structure of the turbot eye (Scophtalmus maximus): A macro-anatomical, light and scanning electron microscopical study.

In fish species, the morphological structure of the eye varies depending on environmental conditions. Morphometric data about the sensory organs of fish is lacking. Therefore, this study aims to describe the morphological structure of the turbot eye using gross, light and scanning electron microscope examinations. The turbot eyeball was found to comprise three layers: the tunica fibrosa bulbi (cornea, sclera), the tunica vasculosa bulbi (choroidea, iris) and the tunica nervea bulbi (retina). The thickness of the centre of the cornea measured approximately 153.14 μm, and the peripheral thickness measured 410.81 μm. The sclera consisted of a two-part cartilage structure that was connected with elastic fibres. The choroideal rete was found in the tunica vasculosa bulbi, and its thickness measured 1.6 ± 0.1 mm. Moreover, no pigment was found in the choroidea. The lens was determined to be a very hard and transparent structure extending towards the cornea. In addition, we detected five ligaments in the equatorial plane of the eye, in which the tendon of the retractor lentis muscle attaches to the lens. Also, there were six extraocular muscles in the turbot. This study is the first to present detailed descriptions of morphological structures and morphometric data for all the layers of the turbot eye. Since the anatomical structure of the eye in fish is variable, it is thought that the data on the turbot eye will contribute to the anatomy literature.