title: Integration of defocus by dual power Fresnel lenses inhibits myopia in the mammalian eye.
abstract: OBJECTIVE
  Eye growth compensates in opposite directions to single vision (SV) negative and positive lenses. We evaluated the response of the guinea pig eye to Fresnel-type lenses incorporating two different powers.
  
  
  METHODS
  A total of 114 guinea pigs (10 groups with 9-14 in each) wore a lens over one eye and interocular differences in refractive error and ocular dimensions were measured in each of three experiments. First, the effects of three Fresnel designs with various diopter (D) combinations (-5D/0D; +5D/0D or -5D/+5D dual power) were compared to three SV lenses (-5D, +5D, or 0D). Second, the ratio of -5D and +5D power in a Fresnel lens was varied (50:50 compared with 60:40). Third, myopia was induced by 4 days of exposure to a SV -5D lens, which was then exchanged for a Fresnel lens (-5D/+5D) or one of two SV lenses (+5D or -5D) and ocular parameters tracked for a further 3 weeks.
  
  
  RESULTS
  Dual power lenses induced an intermediate response between that to the two constituent powers (lenses +5D, +5D/0D, 0D, -5D/+5D, -5D/0D and -5D induced +2.1 D, +0.7 D, +0.1 D, -0.3 D, -1.6 D and -5.1 D in mean intraocular differences in refractive error, respectively), and changing the ratio of powers induced responses equal to their weighted average. In already myopic animals, continued treatment with SV negative lenses increased their myopia (from -3.3 D to -4.2 D), while switching to SV positive lenses or -5D/+5D Fresnel lenses reduced their myopia (by 2.9 D and 2.3 D, respectively).
  
  
  CONCLUSIONS
  The mammalian eye integrates competing defocus to guide its refractive development and eye growth. Fresnel lenses, incorporating positive or plano power with negative power, can slow ocular growth, suggesting that such designs may control myopia progression in humans.
authors.affiliation: School of Psychology, The University of Newcastle, New South Wales, Australia.
authors.forename: Sally A
authors.initials: SA
authors.lastname: McFadden
authors.forename: Dennis Y
authors.initials: DY
authors.lastname: Tse
authors.forename: Hannah E
authors.initials: HE
authors.lastname: Bowrey
authors.forename: Amelia J
authors.initials: AJ
authors.lastname: Leotta
authors.forename: Carly S
authors.initials: CS
authors.lastname: Lam
authors.forename: Christine F
authors.initials: CF
authors.lastname: Wildsoet
authors.forename: Chi-Ho
authors.initials: CH
authors.lastname: To
mesh_terms: D000818:Animals; D058452:Axial Length, Eye; D004195:Disease Models, Animal; D005123:Eye / Q000254:growth & development*; D005139:Eyeglasses; D006168:Guinea Pigs; D009216:Myopia / Q000209:etiology / Q000517:prevention & control*; D055095:Optics and Photonics; D011474:Prosthesis Design
keywords: Fresnel lens; guinea pig; myopia; spectacle lens compensation