Local patterns of image degradation differentially affect refraction and eye shape in chick.
OBJECTIVE
To evaluate visual blur as a mechanism for modulating eye shape.


METHODS
Chicks wore a unilateral full goggle or one of several goggles modified with apertures. After 2 weeks, eyes were measured with refractometry, ultrasound, and calipers, and three retinal regions were assayed for dopamine and DOPAC (3,4-dihydroxyphenylacetic acid).


RESULTS
Goggled eyes were diffusely enlarged or enlarged predominantly along the axial dimension, depending on the goggle. Myopia developed under goggle types inducing primarily axial growth and under some of the goggles inducing diffuse eye expansion. Enlarged eyes remained emmetropic beneath other goggles that caused diffuse eye expansion. Reductions in retinal dopamine and DOPAC were proportional to the eye growth and refraction effects.


CONCLUSIONS
Localized image degradation can cause myopia with predominantly axial expansion, myopia with more diffuse vitreous chamber expansion, or eye expansion without myopia. Robust expansion of the equatorial diameter alone was not observed. The associated alterations in retinal dopamine metabolism are consistent with a hypothesized role of dopaminergic amacrine cells in the visual regulation of eye growth. Besides refraction and overall size, visual blur can affect eye shape; but the goggle responses do not correspond to a simple summation of blur signals across the retina. Therefore, other mechanisms seemingly are needed to account for the full range of refractions and ocular shapes seen in chicks and, by analogy, in humans.
Stone
Richard A
RA
Department of Ophthalmology, University of Pennsylvania, School of Medicine, Scheie Eye Institute, Philadelphia, Pennsylvania 19104-6075, USA. stone@mail.med.upenn.edu
Pendrak
Klara
K
Sugimoto
Reiko
R
Lin
Ton
T
Gill
Amarjeet S
AS
Capehart
Cheryl
C
Liu
Ji
J
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D002645:Chickens; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000378:metabolism*; D005123:Eye / Q000473:pathology*; D005139:Eyeglasses; D006984:Hypertrophy; D009216:Myopia / Q000209:etiology* / Q000378:metabolism*; D012029:Refraction, Ocular; D012160:Retina / Q000378:metabolism; D012683:Sensory Deprivation
D015102:3,4-Dihydroxyphenylacetic Acid; D004298:Dopamine