The Effective Add Inherent in 2-Zone Negative Lenses Inhibits Eye Growth in Myopic Young Chicks

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.