The effective add inherent in 2-zone negative lenses inhibits eye growth in myopic young chicks

Abstract

Purpose: We investigated the effects on refractive development and ocular growth of 2-zone concentric lenses with different negative powers in each of the optical zones, in normal and myopic eyes in young chicks.

Methods: Monocular defocusing lenses were worn for 10-15 days from 12 days of age. Two 2-zone concentric lens types combining -5 and -10 diopter (D) powers, with center zone diameters ranging from 4.5-7.5 mm were tested. One group of chickens wore 2-zone negative lenses from 12 days of age for 10 days, without any previous lens treatment. A second group of 12-day-old chickens were treated initially with -10 D single vision (SV) lenses for 5 days to induce myopia, and then for another 10 days with 2-zone lenses, when the zone of lower power served as a positive addition.

Results: With the 2-zone negative lens treatment alone, the magnitude of on-axis-induced myopia fell between that expected for two negative powers presented in SV lens format, while for eyes first made myopic by pretreatment with -10 SV lenses, the 2-zone negative lenses caused regression of the induced myopia due to inhibitory effects on axial ocular growth, with the greatest effects observed in eyes with higher baseline myopia.

Conclusions: Our results provided further evidence for a role of the peripheral retina in ocular growth regulation. They also lent weight to the idea of using concentric multifocal contact lenses to appropriately manipulate peripheral retinal defocus as one approach to controlling human myopia progression.

Conflict of interest statement

Disclosure: Y. Liu, None; C. Wildsoet, None

Figures

Figure 1.

Schematic summary of the two lens treatment paradigms (A, B) used in this study. SV lenses were included either as a comparison control treatment (A), or as an initial myopia-inducing treatment (B).

Figure 2.

Box plots of changes from baseline in central spherical refractive error (top panel), and corresponding changes of vitreous chamber depth (bottom panel) over the treatment period for (A) the −5C/−10P lens type, (B) −10C/−5P lens type, with varying CZD (on X-axis) ranged from 4.5–7.5 mm. Dashed reference lines: mean changes induced by −10 SV lens. Whisker length: the shorter of 1.5 times the interquartile range and the distance to the extreme.

Figure 3.

Scatter plots of endpoint relative RPR as a function of endpoint on-axis refractive errors for the two lens types. Solid circle: −5C/−10P. Open diamond: −10C/−5P. The mean RPR for eyes wearing −10 SV and plano lenses were +1.58 ± 0.44 D and −0.09 ± 0.83 D, respectively.

Figure 4.

Box plots of changes from baseline in central refractive errors (top panel), and corresponding changes in vitreous chamber depth (bottom panel) after (A) 2-zone lens treatment for 10 days, and (B) −10 SV lens pretreatment for 5 days followed by 2-zone lens treatment for 5 days. Dashed reference lines: mean changes induced by −10 SV lens before replacement with a 2-zone lens. Whisker length: the shorter of 1.5 times the interquartile range and the distance to the extreme.

Figure 5.

Scatter plots of endpoint relative RPR as a function of endpoint on-axis refractive errors for eyes wearing a 2-zone lens for 5 days after pretreatment with a −10 SV lens for 5 days. Solid circle: −5C/−10P. Open diamond: −10C/−5P (bottom panel). The mean RPR induced by −10 SV lens worn for 10 days was 1.58 ± 0.44 D.