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J. M. Schartau, R. H. H. Kröger, B. Sjögreen; Dopamine Induces Optical Changes in the Cichlid Fish Lens. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4343.
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In the South American cichlid fish Aequidens pulcher, dark adaptation alters the functional structure of the retina through retinomotor movements. During dusk the cone and rod outer segments trade places and the retina becomes functionally monochromatic. Dopamine has previously been linked closely to dark/light adaptation in the retina and the level of dopamine in the eye fluctuates over the day with low concentration during the night. Recent studies have revealed that the optics of the cichlid eye also undergo dark adaptation. During dusk the spherical aberration of the multifocal lens is significantly reduced and the lens becomes almost monofocal. We therefore wanted to test whether dopamine also was involved in the lens light/dark adaptation.
An organ-bath system was constructed and the spherical aberration of the lens was measured with laser scanning and visualized with schlieren photography. Both lenses from each individual were used, alternating between left and right as control. The lenses where treated with dopamine agonists, concentrations ranging from 10-6 to 10-3 mol/l. Control lenses remained untreated. The spherical aberration was measured in each lens four times, the first immediately after the experimental start and the last at 240 minutes.
We detected significant changes in the optical properties in the treated groups compared to the control group. Treatment with dopamine reduces the refractive power in the periphery of the cichlid lens. Effects were visible from 65 percent of the lens radius and outwards, 0 percent being the very center of the lens and 100 percent the fibrous capsule. Increased levels of dopamine resulted in an increased response.
Our results suggest that dopamine is a key modulator in the dark/light adaptation of the cichlid lens. Dark adaptation leads to an increase of refractive power in the periphery of the lens. Complete depletion of dopamine in the eye gives a similar but stronger effect. Treatment with dopamine gives the opposite effect to dark adaptation and reduces the refractive power in the periphery of the lens. Whether there are further mediators involved in this regulation remains to be investigated.
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