title: The effect of two-zone concentric bifocal spectacle lenses on refractive error development and eye growth in young chicks.
abstract: OBJECTIVE
  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.
authors.affiliation: Center for Eye Disease and Development, University of California Berkeley School of Optometry, Berkeley, California, USA. marialiu@berkeley.edu
authors.forename: Yue
authors.initials: Y
authors.lastname: Liu
authors.forename: Christine
authors.initials: C
authors.lastname: Wildsoet
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002645:Chickens; D003263:Contact Lenses, Hydrophilic; D005123:Eye / Q000254:growth & development*; D005139:Eyeglasses; D006956:Hyperopia / Q000209:etiology / Q000503:physiopathology*; D009216:Myopia / Q000209:etiology / Q000503:physiopathology*; D011474:Prosthesis Design; D012029:Refraction, Ocular / Q000502:physiology; D012160:Retina / Q000503:physiopathology*