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.
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