Study of Theories About Myopia Progression (STAMP)
Condition: Myopia
MeSH terms: Myopia; Disease Progression
Study type: Interventional

Summary: 
      At this time, we do not know what causes a child to become more nearsighted (myopic). STAMP
      will help us better understand nearsightedness in children. Children will be randomly chosen
      to wear regular glasses (single vision lenses) or no-line bifocal glasses (progressive
      addition lenses) for the first year of the study. All children will wear regular glasses for
      the second year of the study. STAMP will compare how the eye changes shape in the two groups
      to help us understand why children become nearsighted. The two theories of myopia progression
      that are being evaluated are based on different factors. One theory is based on environmental
      factors such as extended near work while the other theory is based on genetically coded
      factors.
    

Detailed description: 
      Eligible children will be enrolled, randomized, and followed at six-month intervals for two
      years with all children wearing single vision lenses for the second year. At each visit,
      complete measurements of the components of the eye will be made to explain the mechanism
      responsible for the Progressive Addition Lens (PAL) treatment effect and why it occurs mainly
      during the first year of bifocal wear (Gwiazda et al. 2003). While hyperopic retinal blur
      (blur at the back of the eye) due to accommodative lag (poor focusing when doing close work)
      has been proposed as a possible mechanism driving myopia progression (Gwiazda et al. 1993),
      others have shown that accommodative lag accompanies rather than precedes the onset of myopia
      (Mutti et al., 2006). This suggests that accommodative lag is a result of another possible
      mechanism resulting in myopia progression such as crystalline lens-induced ciliary-choroidal
      tension (a model in which the lens in the eye is stretched and is not as good at focusing up
      close) (Mutti et al., 2000). According to this proposed mechanism, high accommodative lag in
      myopia results from increased crystalline lens tension that is transmitted through the
      choroid (an outside layer of the eye). This tension results in restricted equatorial (the
      vertical dimension of the eye) eye growth with no axial (front to back) restriction to eye
      growth and yields a prolate ocular shape (an eye that is longer than it is wide) in myopes
      (Mutti et al., 2000).

      Comparisons: Refractive error (glasses prescription), axial length (length of the eye),
      peripheral eye shape, accommodation (focusing ability), corneal shape (shape of the front of
      the eye), anterior chamber depth, crystalline lens thickness and curvatures (shape of the
      lens in the eye), central and peripheral higher-order aberrations (how well light focuses in
      the eye), and phoria (eye alignment) will be measured at six-month intervals. The primary
      study outcome is refractive error measured by cycloplegic autorefraction. Comparison of the
      biometric data collected both during the first year when the PAL intervention is present and
      during the second year when the PAL intervention is removed will allow us to differentiate
      between the two theories under consideration. We will also evaluate whether the modest PAL
      treatment effect that has been reported during the first year of PAL wear is permanent.
    

Intervention name(s): progressive addition spectacle lens (bifocal); Single Vision Lenses (SVLs)
Intervention type(s): Device; Device
Intervention description(s): Progressive addition lenses (PAL) with a +2.00 D add.; Single vision spectacle lenses.
Other intervention name(s): PAL; SVL
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment
Keywords: myopia progression; bifocal