The effect of two-zone concentric bifocal spectacle lenses on refractive error development and eye growth in young chicks

Abstract

Purpose: To characterize the effects on refractive error development and eye growth in young chicks of two-zone concentric lens designs, which differentially affect the defocus experiences of central and peripheral retinal regions.

Methods: Monocular defocusing lenses were worn for 5 days from 17 days of age. Four two-zone concentric lens designs (overall optical zone diameter, 10 mm) combining plano with either -5- or +5-D power were used. Lens designs were as follows: (1) +5 D center (+5C), (2) +5 D periphery (+5P), (3) -5 D center (-5C), and (4) -5 D peripheral (-5P), with plano in periphery for all C-designs and in the center for P-designs. Five central zone diameters (CZDs) were tested, ranging from 2.5 to 6.5 mm in 1-mm increments. Plano, +5- and -5-D single-vision (SV) lenses were used as the control. A minimum of six birds were included in each lens group.

Results: For the two-zone lenses, the P designs (i.e., peripheral defocus) had greater effects than the C designs (i.e., central defocus) on both on-axis eye growth and refractions. All but the 6.5-mm CZD +5P lens induced larger changes than the +5SV lens. The +5C lenses with CZD less than 5.5 mm had little effect. The two-zone -5-D lenses had less effect than the -5SV lens, and only the 6.5-mm CZD lens of the -5C series had a significant effect.

Conclusions: The results demonstrate that peripheral defocus can influence both peripheral and central refractive development. The inhibitory effect on axial eye growth of the +5P lenses opens the possibility that appropriately designed concentric lenses may control the progression of human myopia.

Figures

Figure 1.

Boxplots of central refractive error changes (a and b, top), and corresponding axial length changes (a and b, bottom) over the treatment period for (a) the +5C lens designs and (b) the +5P lens designs. Central zone diameters (CZD, on X-axis) ranged from 2.5 to 6.5 mm. Dashed reference lines: mean changes induced by +5SV lens; solid lines: mean change induced by the plano lens. Whisker length denotes the shorter of 1.5 times the interquartile range and the distance to the extreme.

Figure 2.

Boxplots of central refractive error changes (a and b, top) and axial length changes (a and b, bottom) over the treatment period for (a) the −5C two-zone lens designs and (b) the −5P two-zone lens designs. CZDs ranged from 2.5 to 6.5 mm. Dashed reference line: mean change induced by the −5SV lens; solid lines: mean change induced by the plano lens.

Figure 3.

RPRs plotted as a function of changes in on-axis refractive error for each of the four two-zone lens types.