The suspension of the crystalline lens in the eye was studied in 11 species of teleost (bony fish) from 10 families and 7 orders by light and electron microscopy. In all species there were 4-5 ligaments in about the equatorial plane of the eye, in which also the tendon of the retractor lentis muscle attaches to the lens. In two cichlid species two additional ligaments were found running from the mid-posterior surface of the lens to the optic nerve head, where they attach to the falciform process. Lens suspension in teleosts is more complex than previously described and well-suited to firmly keep the heavy spherical lens in position for well-focused vision.

One of the reasons that the crystalline lenses of vertebrate eyes are highly transparent is that most of the cells have broken down all of their organelles, including the nuclei. These cells can neither synthesize new proteins nor generate energy by electron transport in the mitochondria. Only in the peripheral layers--in the cichlid fish Aequidens pulcher, beyond 92% of the lens radius--are there cells with full complements of organelles. We report here that the optical properties of the lens change between the light-adapted and dark-adapted states in A. pulcher. Changes occur even in cell layers free of organelles, and they occur in parallel with changes in retinal function between the light-adapted (all-cone, color vision) and dark-adapted (all-rod, grayscale vision) states. Depleting the eye of dopamine also caused changes in the optical properties similar to those of dark adaptation. Our results indicate that the refractive index of the organelle-free lens fiber cells can be adjusted quickly and accurately.

The crystalline lens in the cichlid fish Aequidens pulcher undergoes a transformation of its optical properties every dawn and dusk as the eye adapts to changes in light conditions. During dusk the transformation result in an increase of the refractive power in the lens cortex, the outermost 40 percent. The change is thought to match the optical properties of the lens to the requirements of the retina. Using a short term in vitro lens culturing system together with optical measurements we here present data that confirm that the optical properties of the lens can change within hours and that dopamine influences the optical properties of the lens. Dopamine yields dose-dependent decrease of the refractive power in the lens cortex. The D1-agonist SKF-38393 induces a similar decrease of the refractive power in the cortex, while the D2-agonist quinpirole has no effect. The effect of dopamine can be blocked by using the D1-antagonist SCH 23390. Our results suggest that dopamine alone could be responsible for the light/dark adaptive optical changes in the lens, but the involvement of other signaling substances cannot be ruled out.

Culturing whole lenses is a frequently used method for studying regulatory events on the lens in controlled environments. The evaluation methods used often fall under two categories, molecular or optical. The main benefit from optical measurements is that they directly detect changes in the lens' main function, i.e. refracting light. However, these measurements often have rather low resolution or yield results open for subjective interpretation. Here we present a short-term crystalline lens culturing technique combined with a high-resolution optical measuring method. There are two main advantages of using teleost lenses compared to mammalian lenses. Teleost tissue generally has a higher tolerance than mammalian tissue with regard to temperature and nutrient fluctuations. Teleost lenses are structurally more robust and can be excised from the eye without disturbing form or function. The technique is developed for short-term culturing (3 h), however, the lenses appear viable for at least 24 h and longer culturing may be possible. The technique is resistant to small variations in osmolarity and yields quantitative datasets for further analyses and statistical treatment.