Development of Experimental Myopia in Chicks in a Natural Environment.
The hypothesis that outdoor exposure might protect against myopia has generated much interest, although available data find only modest clinical efficacy. We tested the effect of outdoor rearing on form-deprivation myopia in chicks, a myopia model markedly inhibited by high-intensity indoor laboratory lighting.



Unilaterally goggled cohorts of White Leghorn chicks were maintained in a species-appropriate, outdoor rural setting during daylight hours to the extent permitted by weather. Control chicks were reared indoors with incandescent lighting. Besides ocular refraction and ultrasound, we determined dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) content in retina and vitreous and measured mRNA expression levels of selected clock and circadian rhythm-related genes in the retina/RPE.



Myopia developed in the goggled eyes of all cohorts. Whereas outdoor rearing lessened myopia by 44% at 4 days, a protective effect was no longer evident at 11 days. Outdoor rearing had no consistent effect on retinal or vitreous content of dopamine or DOPAC. Conforming to prior data on form-deprivation myopia, retina and vitreous levels of DOPAC were reduced in goggled eyes. Compared with contralateral eyes, the retinal expression of clock and circadian rhythm-related genes was modestly altered in myopic eyes of chicks reared indoors or outdoors.



Outdoor rearing of chicks induces only a partial decrease of goggle-induced myopia that is not maintained, without evidence that retinal dopamine metabolism accounts for the partial myopia inhibition under these outdoor conditions. Although modest, alterations in retinal gene expression suggest that studying circadian signals might be informative for understanding refractive mechanisms.
Department of Ophthalmology University of Pennsylvania School of Medicine, Scheie Eye Institute, Philadelphia, Pennsylvania, United States.
Richard A
RA
Stone
Department of Ophthalmology University of Pennsylvania School of Medicine, Scheie Eye Institute, Philadelphia, Pennsylvania, United States.
Yuval
Y
Cohen
Department of Ophthalmology University of Pennsylvania School of Medicine, Scheie Eye Institute, Philadelphia, Pennsylvania, United States.
Alice M
AM
McGlinn
Laboratory of Avian Medicine and Pathology, University of Pennsylvania School of Veterinary Medicine, New Bolton Center, Kennett Square, Pennsylvania, United States.
Sherrill
S
Davison
Laboratory of Avian Medicine and Pathology, University of Pennsylvania School of Veterinary Medicine, New Bolton Center, Kennett Square, Pennsylvania, United States.
Susan
S
Casavant
Department of Ophthalmology University of Pennsylvania School of Medicine, Scheie Eye Institute, Philadelphia, Pennsylvania, United States.
James
J
Shaffer
Department of Physiology and Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States.
Tejvir S
TS
Khurana
Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States 5Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Medical Center, Decatur, Georgia, United States.
Machelle T
MT
Pardue
Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, United States 7Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, United States.
P Michael
PM
Iuvone
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002645:Chickens; D002940:Circadian Rhythm / Q000502:physiology*; D003623:Dark Adaptation / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D008027:Light; D009216:Myopia / Q000503:physiopathology*; D012333:RNA, Messenger / Q000235:genetics; D012029:Refraction, Ocular / Q000502:physiology*; D012160:Retina / Q000378:metabolism; D012683:Sensory Deprivation; D014822:Vitreous Body / Q000378:metabolism
D012333:RNA, Messenger; D015102:3,4-Dihydroxyphenylacetic Acid