Purchase this article with an account.
Y. Liu, C. F. Wildsoet; With Appropriately Designed Two-Zone Concentric Bifocal Spectacle Lenses, Peripheral Defocus Significantly Influences Refractive Development in Chicks. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1617.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Recent studies in primates suggest a critical role for the peripheral retina in regulating on-axis eye growth. Here we used a novel lens design to present different defocus signals to the central and peripheral retina, to further characterize the role of the peripheral versus central retina in guiding emmetropization.
Four 2-zone concentric bifocal lens designs (L1: +5D center (C), L2: -5D C, L3: +5D periphery (P), L4: -5D P (plano in second zone in all cases), were used to differentially expose the central and peripheral retina to defocus. Two central optical zone diameters, 2.5 and 3.5 mm, were tested, corresponding to visual field projections of ~ 27 and 37 degrees respectively (total lens diameter=12 mm). Three single vision (SV) lenses (plano, +5 & -5D) were included as controls. The lenses were fitted monocularly to 17 days old White-Leghorn chicks (6 per group), and worn for 5 days. High frequency ultrasonography and retinoscopy were performed at baseline and at the end of experiments.
For all of the findings reported below, the diameter of the central optical zone was not a significant factor in determining endpoint refractions (p=0.87). The effects of lenses with power limited to the central zone (L1: +0.24, 1.27D, L2: +0.14, 2.45D) were indistinguishable from those of plano lenses. In contrast, when the defocusing power was limited to the lens periphery, chicks showed a consistent change in their on-axis refractions. Interocular difference (means, SDs) were: L3: +4.84, 1.02D; L4: -3.90, 0.84D. Furthermore, the L3 lenses in which the plus power was limited to the peripheral zone, induced significantly more hyperopia than the +5D SV lenses (p=0.036). Interocular differences in refraction were best explained by differences in vitreous chamber depth (R2 = 0.56).
For the 2-zone lens designs tested, peripheral defocus had a greater effect than central defocus on both on-axis eye growth and refractions, with the effects of the plus-peripheral lenses being also greater than that of matching single vision lenses. The latter result argues against a simple weighted average of the defocus experience imposed by the two lens zones as the determinant of the response. An alternative model involving imposed changes in ocular spherical aberration also does not fully explain the results. A more complex model is required.
This PDF is available to Subscribers Only