Refractive plasticity of the developing chick eye

Abstract

We have developed a lightweight plastic goggle with rigid contact lens inserts that can be applied to the eyes of newly hatched chicks to explore the range and accuracy of the developmental mechanism that responds to retinal defocus. Convex and concave lenses of 5, 10, 15, 20 and +30D were applied to one eye on the day of hatching. The chick eye responds accurately to defocus between -10 and +I5D, although hyperopia develops more rapidly than myopia. Beyond this range there is first a levelling off of the response and then a decrease. The resulting refractive errors are caused mainly by increases and decreases in a.xial length, although high levels of hyperopia are associated with corneal flattening. If + 10 D defocusing lenses are applied nine days after hatching the resulting myopia and hyperopia are equal to about 80% of the inducing power. After one week of inducing myopia and hyperopia with ± !0 D lenses, the inducing lenses were reversed. In this case, the refractive error did not reach the power of the second lens after another week of wear. Instead, astigmatism in varying amounts (0-12 D) was produced, being greater when reversal was from plus to minus. Finally, astigmatism can also be produced by applying 9 D toric inducing lenses on the day of hatching. The astigmatism produced varies from 2 to 6 D, and the most myopic meridian coincides with the power meridian of the inducing lens. This astigmatism appears to be , primarily due to corneal toricity. Furthermore, the greatest magnitude of astigmatism was produced when the piano meridian of the inducing lens was placed 45" from the line of the palpebral fissure.

Ciliary body thickness in unilateral high axial myopia

“…23,24 The same occurs if one puts a positive lens over the eye in chicks and monkeys. 25,26 The range of lens powers compensated for is greater in chicks than in monkeys, although monkeys can also compensate for stronger lenses if the lens power is stepped up gradually. 25,27 Similar mechanism may also be active in humans, however this entails further research.…”

Diurnal Rhythms of Spherical Refractive Error, Optical Axial Length, and Power in the Chick

“…For induced differences between treated and untreated eyes for lenses between À10 D and þ18 D, 48,49 MOR and axial length have a linear dependence with a slope equal to the À26 D/mm, as predicted (Appendix, equation A2). Thus, length changes almost completely account for long-term experimental induction of MOR, 48,49 without considering changes in power.…”

Prevalence and associated factors of myopia among primary and middle school-aged students: a school-based study in Guangzhou

“…9 Evidences from animal experiments indicated that an accommodative lag during prolonged near work lead to hyperopic defocus on the retina which might result in excessive growth of the eye and a myopic refractive error. 10,11 A cohort study in Australia showed that primary school students with incident myopia were more likely to spend significantly more time studying and reading, 12 and a cross-sectional study in Beijing also demonstrated that a higher prevalence of myopia in highschool students was associated with shorter near work distance. 7 However, there have also been some studies reporting a weak or absent association between heavier load of near work and the prevalence or incidence of myopia.…”