Constant light affects retinal dopamine levels and blocks deprivation myopia but not lens-induced refractive errors in chickens

Abstract

Chickens were raised with either translucent occluders or lenses, both under normal light cycles (12–h light/12–h dark) and in constant light (CL). Under normal light cycles, eyes with occluders became very myopic, and eyes with lenses became either relatively hyperopic (positive lenses) or myopic (negative lenses). After the treatment, retinal dopamine (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 DOPAC (-40%) and DA (-30%) after 2 weeks of deprivation. No changes in retinal serotonin levels were found. Retinal DA or DOPAC content remained 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 reduced (8 days CL) or entirely blocked (13 days CL). Lens-induced changes in eye growth were not different after either 6 or 11 days in CL, compared 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 changes in refraction may not be dependent on dopaminergic pathways whereas deprivation myopia requires normal diurnal DA rhythms to develop.

Vitamin D in Dry Eye and Myopia

“…These studies have been confirmed using guinea pigs (Dong et al, 2011a) in form-deprivation myopia, reductions in both dopamine and its metabolites were observed. Other studies observing chickens also showed similar results (Bartmann et al, 1994;Megaw et al, 2006;Stone et al, 1989b).…”

“…FDM in chickens could be suppressed by constant light (Bartmann et al, 1994) and a similar inhibitory effect on myopia has been demonstrated in rhesus monkeys exposed to high intensity of light (range between 18000 and 28000 Lux) (Smith et al, 2012a). However, Lauber (1987) raised that constant light could induce glaucoma in the chicks about three decades earlier.…”

“…The underlying mechanism may be related to accommodation, the visual clue is mostly removed in FDM, while accommodation can compensate the defocused image in LIM. Reductions of dopamine and its metabolites were observed with 13-day constant light, accompanying myopia inhibition; whereas eye growth still continued in LIM (Bartmann et al, 1994). This may be indicating LIM is not dopamine rhythm dependant as observed in FDM.…”

“…However, Bartmann et al (1994) found that constant light only had inhibitory effect on myopia development in chickens when the eyes were form deprivation myope (FDM), with no significant changes in eye with lens induced myopia (LIM), implying that the two types of myopia have different triggers; while normal diurnal dopamine rhythms is required in developing FDM, LIM may not be developed via dopaminergic pathways.…”

Myopia, Light and Circadian Rhythms

“…The use of modified translucent occluders demonstrates that retinal dopamine levels inversely correlate with the degree of axial elongation (Stone, Pendrak et al 2006). Retinal dopamine levels exhibit a bidirectional response to retinal blur in chicks, with lens-induced myopia decreasing and hyperopia increasing the levels respectively (Guo, Sivak et al 1995) although this effect is not universally reported (Bartmann, Schaeffel et al 1994). The increase in retinal dopamine associated with the slowing of axial growth in lens-induced hyperopia parallels recovery from form-deprivation myopia in the chick where a similar relationship between dopamine level and axial growth is reported (Pendrak, Nguyen et al 1997).…”