Myopia develops in chickens if their eyes are covered with translucent occluders. The occluders (made from thin plastic foil) reduce the contrast of the retinal image but attenuate image brightness by only 0.3 log units.
Since it is known that a drop in image brightness causes a drop in dopamine release from retina and since myopia seems to be linked to a drop in dopamine release,

Marita Feldkaemper studied whether myopia can be induced by low light.

She found that
(1) reducing image contrast is much more effective to produce myopia ( -- )
(2) but that some myopia develops also with grey filters ( -- )
(3) that dopamine release drops similarly in both cases.

She concluded that near work at low light levels may increase the risk of myopia.
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Her major project is currently to find retinal messengers that are involved in the development of experimental hyperopia and myopia (induced by plus or minus lenses, respectively).

Results by Hartmut Schwahn, Sigrid Diether and Gabi Hagel suggested that myopia development involves different messengers than hyperopia development. Marita Feldkaemper studies gene expression in retinas of differently treated chicks, using mRNA differential display. On the gel on the left, band patterns (showing DNA fragments) from the retinas of chickens treated with plus or minus lenses can be compared.

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