Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks

Abstract

This study analyzed the luminance and color emmetropization response in chicks treated with the nonselective parasympathetic antagonist atropine and the sympathetic β-receptor blocker timolol. Chicks were binocularly exposed (8hr/day) for four days to one of three illumination conditions: 2 Hz sinusoidal luminance flicker, 2 Hz sinusoidal blue/yellow color flicker, or steady light (mean 680 lux). Atropine experiments involved monocular daily injections of either 20 μl of atropine (18 nmol) or 20 μl 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 ± 0.021 mm) and color flicker (−0.054 ± 0.017 mm), and a reduction in vitreous chamber depth with luminance flicker (−0.095 ± 0.023 mm), evoking a hyperopic shift in refraction (3.40 ± 1.77 D). Timolol produced an increase in axial length with luminance flicker (0.045 ± 0.030 mm) and a myopic shift in refraction (−4.07 ± 0.92 D), while color flicker caused a significant decrease in axial length (−0.046 ± 0.017 mm) that was associated with choroidal thinning (−0.046 ± 0.015 mm). The opposing effects on growth and refraction seen with atropine and timolol suggest a balancing mechanism between the parasympathetic and β-receptor mediated sympathetic system through stimulation of the retina with luminance and color contrast.

The Effects of 0.01% Atropine on Adult Myopes’ Contrast Sensitivity

“…Although the antimyopia mechanism of atropine is not fully understood, recent experiments have shown that atropine may exert its myopiaprotective effect mainly through muscarinic receptors on retina and sclera, stopping the remodeling and thinning of sclera and the consequent axial lengthening of the eye, even at a low concentration (Sánchez-González et al, 2020;Upadhyay and Beuerman, 2020). Moreover, topical atropine could cause pupil dilation, decrease of accommodation amplitude and change in corneal curvature, lens thickness, anterior chamber depth and vitreous chamber depth (Qu et al, 2006;Kumaran et al, 2015;Goldberg and Rucker, 2016;Yam et al, 2019;Upadhyay and Beuerman, 2020). It was proved that CS is affected by optical factors (e.g., aberration based on pupil size and intraocular forward scattering) as well as retinal and brain processing (Radhakrishnan et al, 2004;Yamaguchi et al, 2011;Kamiya et al, 2014;Karatepe et al, 2017).…”

Effect and correlation of intraocular pressure on the refractive status of children and adolescents

“…However, FDM models and LIM lens models in chicks confirmed [37] that a significant reduction in IOP had little effect on the development of myopia. In another animal study [38] , tissue may be less likely to contract under the influence of a small drop in intraocular pressure. The study of Yan Hong et al [39] showed that the normal range of IOP had no correlation with diopter and axial length, so the local application of IOP drugs to control the development of myopia may not be effective.…”

5.4: The Effects of 0.01% Atropine on Adult Myopes' Contrast Sensitivity

“…Although the anti-myopia mechanism of atropine is not fully understood, recent experiments have shown that atropine may exert its myopia-protective effect mainly through muscarinic receptors on retina and sclera, stopping the remodeling and thinning of sclera and the consequent axial lengthening of the eye, even at a low concentration (Sánchez-González et al, 2020; Upadhyay and Beuerman, 2020). Moreover, topical atropine could cause pupil dilation, decrease of accommodation amplitude and change in corneal curvature, lens thickness, anterior chamber depth and vitreous chamber depth (Qu et al, 2006;Kumaran et al, 2015;Goldberg and Rucker, 2016;Yam et al, 2019;Upadhyay and Beuerman, 2020). It was proved that CS is affected by optical factors (e.g., aberration based on pupil size and intraocular forward scattering) as well as retinal and brain processing (Radhakrishnan et al, 2004;Yamaguchi et al, 2011;Kamiya et al, 2014;Karatepe et al, 2017).…”