The eye is in dynamic equilibrium. You can put goggles on a chicken with different kinds of focuses, and get one eye to elongate and one to shrink. Although, it is unclear what the exact connection is between dopamine and the eyeball growth effect. Its not clear whether its a receptor-mediated effect. There are reciprocal systems between melatonin and dopamine.
Dopamine goes up in the light, melatonin goes down.
Melatonin is made in photoreceptors. Dopamine levels affect the levels of Melatonin. If melatonin is high, you can introduce dopamine and melatonin will decrease. In this way Dopamine acts like a light-adaptation signal. Retinomotor movements Our pupils adjust to light, just as in other mammals.