CONSTANT LIGHT AFFECTS RETINAL DOPAMINE LEVELS AND BLOCKS DEPRIVATIONMYOPIA BUT NOT LENS-INDUCED REFRACTIVE ERRORS IN CHICKENS

Chickens were raised with either translucent occluders or lenses, both under normal light cycles (12-h light/12h dark) and in constant light (CL). Under normal light cycles, eyes with occluders became very myop ic, and eyes with lenses became either relatively hyperopic (positive lenses) or myopic (negative lenses). After the treatment, retinal dopa mine (DA), DOPAC, and serotonin levels were measured by high-pressure liquid chromatography (HPLC-EC). A significant drop in daytime retinal DOPAC (-20%) was observed after 1 week of deprivation, and in both DO PAC (-40%) and DA (-30%) after 2 weeks of deprivation. No changes in r etinal serotonin levels were found. Retinal DA or DOPAC content remain ed unchanged after 2 or 4 days of lens wearing even though the lenses had already exerted their maximal effect on axial eye growth. When the chickens were raised in CL, development of deprivation myopia was red uced (8 days CL) or entirely blocked (13 days CL). Lens-induced change s in eye growth were not different after either 6 or 11 days in CL, co mpared to animals raised in a normal light cycle. Thirteen days of CL resulted in a dramatic reduction of DA and DOPAC levels, but serotonin levels were also lowered. The results suggest that lens-induced chang es in refraction may not be dependent on dopaminergic pathways whereas deprivation myopia requires normal diurnal DA rhythms to develop.