Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks.
Vision Res
; 122: 1-11, 2016 05.
Article
em En
| MEDLINE
| ID: mdl-26971621
ABSTRACT
This study analyzed the luminance and color emmetropization response in chicks treated with the nonselective parasympathetic antagonist atropine and the sympathetic ß-receptor blocker timolol. Chicks were binocularly exposed (8h/day) for 4days to one of three illumination conditions 2Hz sinusoidal luminance flicker, 2Hz sinusoidal blue/yellow color flicker, or steady light (mean 680lux). Atropine experiments involved monocular daily injections of either 20µl of atropine (18nmol) or 20µl of phosphate-buffered saline. Timolol experiments involved monocular daily applications of 2 drops of 0.5% timolol or 2 drops of distilled H2O. Changes in the experimental eye were compared with those in the fellow eye after correction for the effects of saline/water treatments. Atropine caused a reduction in axial length with both luminance flicker (-0.078±0.021mm) and color flicker (-0.054±0.017mm), and a reduction in vitreous chamber depth with luminance flicker (-0.095±0.023mm), evoking a hyperopic shift in refraction (3.40±1.77D). Timolol produced an increase in axial length with luminance flicker (0.045±0.030mm) and a myopic shift in refraction (-4.07±0.92D), while color flicker caused a significant decrease in axial length (-0.046±0.017mm) that was associated with choroidal thinning (-0.046±0.015mm). The opposing effects on growth and refraction seen with atropine and timolol suggest a balancing mechanism between the parasympathetic and ß-receptor mediated sympathetic system through stimulation of the retina with luminance and color contrast.
Palavras-chave
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Atropina
/
Timolol
/
Antagonistas Muscarínicos
/
Antagonistas Adrenérgicos beta
/
Visão de Cores
/
Emetropia
/
Midriáticos
Limite:
Animals
Idioma:
En
Revista:
Vision Res
Ano de publicação:
2016
Tipo de documento:
Article