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Diurnal growth rhythms in the chicken eye: relation to myopia development and retinal dopamine levels
1Augenklinik der Universität Tübingen, Abt. Pathophysiologie des Sehens und Neuroophthalmologie, Germany.
Insights
Depriving young chickens of clear vision causes myopia by preventing nighttime eye growth inhibition. Dopamine pathways are crucial for regulating eye growth and preventing myopia development.
Area of Science:
- Ophthalmology
- Neuroscience
- Developmental Biology
Background:
- Young chickens deprived of clear vision develop axial myopia rapidly.
- Retinal dopamine levels decrease significantly with visual deprivation.
- Diurnal variations in retinal dopamine levels suggest potential diurnal differences in eye growth.
Purpose of the Study:
- To investigate the diurnal patterns of axial eye growth in young chickens.
- To determine the role of retinal dopamine in deprivation myopia.
- To understand the mechanisms underlying growth inhibition and eye elongation.
Main Methods:
- Utilized translucent occluders to induce visual deprivation in young chickens.
- Administered 6-hydroxy-dopamine (6-OHDA) to suppress dopaminergic pathways.
- Monitored axial eye growth and refractive state under various light conditions.
Main Results:
- Chickens' eyes grew during the day but shrank at night; deprivation myopia resulted from a lack of nighttime growth inhibition.
- Visual deprivation led to continuous eye growth, both day and night.
- Suppression of dopaminergic pathways with 6-OHDA prevented deprivation myopia and restored nighttime growth inhibition.
Conclusions:
- Deprivation myopia in chickens is primarily due to the absence of normal nighttime eye growth inhibition.
- The dopaminergic system plays a critical role in regulating diurnal eye growth rhythms and preventing myopia.
- Targeting retinal dopamine pathways may offer therapeutic strategies for myopia control.
Abstract:
1. If the eyes of young chickens are deprived of clear vision by translucent occluders, they develop considerable amounts of axial myopia within days. At the same time, the day time retinal dopamine levels drop by about 30%. Because the retinal dopamine levels of normally sighted chicks also differ diurnally and are low at night, we expected that the rate of axial eye growth might also differ during this time. 2. Unexpectedly, eyes grew in length only during the day (about 0.13 mm/day) and even shrank during the night (about -0.04 mm/night, average net growth +0.09 mm in 24 h). 3. If the eyes were occluded, they grew both during the day and also at night (average net growth: +0.16 mm in 24 h). Therefore, development of deprivation myopia was a result of the lack of growth inhibition at night rather than of excessive growth during the day when the actual deprivation occurred. 4. Suppression of dopaminergic retinal pathways by intravitreal injections of the neurotoxin 6-hydroxy-dopamine (6-OHDA) also suppressed development of deprivation myopia and it restored the growth inhibition at night. With normal visual experience, the drug had no effect on axial eye growth and refractive state. 5. Diurnal growth rhythms of the eyes disappeared under continuous light.(ABSTRACT TRUNCATED AT 250 WORDS)