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S. McCarthy, P. Megaw, I. Morgan; How Important Is Dopamine in the Control of Eye Growth?. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1733.
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Dopamine has long been recognised as a candidate in eye growth regulation, with evidence suggesting dopamine release is reduced under conditions that increase eye growth. If dopamine is a global eye growth regulator, then dopamine release should increase under conditions that suppress eye growth. This hypothesis was tested by comparing the release of dopamine in two paradigms in which eye growth is inhibited: the response to plus lenses (suppression of normal growth) and the effects of atropine on eye growth in FDM (suppression of induced excessive growth).
Paradigm 1: chickens were fitted with +10D or -10D lenses. On day 1 and 7 of lens wear, vitreous samples were taken at 0 (dark), 2.5, 6 & 12 hours after lights on. Paradigm 2: chickens fitted with diffusers were intravitreally injected with of 20mM (concentration in the syringe, injection volume 10µL) of atropine daily for 7 days. Vitreous bodies were sampled 6 hours after lights on. Dopamine release was monitored by the accumulation of DOPAC in the vitreous, measured by HPLC-ED. Axial lengths were measured by A-scan ultrasound on day 7.
After 7 days of plus lens wear, eyes were significantly shorter than their CLC eyes. Vitreal DOPAC was reduced in chickens fitted with plus lenses over the whole light phase on both day 1 and day 7 of lens wear, to a similar extent to that observed in response to minus lenses. Daily atropine injections suppressed the excessive axial elongation induced by diffusers, but vitreal DOPAC accumulation remained depressed.
These results suggest that dopamine release is not systematically related to the rate of eye growth. Plus and minus lenses depress dopamine release to a similar extent, despite their quite different effects on growth, confirming previous experiments which were ambiguous due to pronounced effects on dopamine release of the mounts . When apparently normal eye growth was restored by atropine treatment in the form-deprivation paradigm, dopamine release remained reduced. This evidence conflicts with our recent report that dopamine plays a crucial role in the suppression of FDM by brief normal vision . These results suggests that dopamine release is not the universal eye growth regulator, although it may be important in certain circumstances.1. Boelen, M.K., et al., (1999) Retinal dopamine does not decode for the sign of defocus, ARVO. Abstract #963.2. McCarthy, C.S., et al., Dopaminergic agents affect the ability of brief periods of normal vision to prevent form-deprivation myopia. Exp Eye Res, 2007. 84(1): p.100-7.
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