how can spectacle lenses help for myopia control?
- undermining makes it worse
- multifocals offer some benefit
what were the names of the 2 large scale PAL trials?
- Edwards et al. (2002)
- COMET (Gwiazda et al. 2003)
Edwards et al. (2002) study showed:
-single vision: -1.26 D
-PALs= -1.12 D
treatment effect= 11%
COMET (Gwiazda et al. 2003) study showed:
-single vision: -1.48 D
PALs= -1.28 D
treatment effect= 13%
study design (participants, random groups) on Executive bifocals study (Cheng et al. 2010)
- randomized clinical trial of 135 myopic Chinese Candian children
- randomly assigned to: single vision lenses, +1.50D executive bifocals, or +1.50D executive with 3pd base-in segment
results of on Executive bifocals study (Cheng et al. 2010)
-single vision: -1.56D
-bifocal: -0.96D
-prism bifocal: -0.70D
treatment effect on bifocal= 31% and on prism bifocal= 34%
myopia progression at 2 years in the ATOM1 (N=400) study
- 28 in 1% group
1. 20D in placebo group
mean myopic progression at 2 years in ATOM2 study (N=400) of different concentrations
- 30 D in 0.5% group
- 38 D in 0.1% group
- 49 D in 0.01% group
how does atropine work to control myopia?
- action on muscarinic receptors in retina
- atropine is non-selective muscarinic antagonist
- selective muscarinic antagonist could target M1 receptors in retina
what did the Pirenzepine study show?
- selective anti-muscarinic
- one year randomized trial of 174 children
- 51% effect
- but side effects of stinging, pupil dilation, and short term blurring
design of RGP lenses: the CLAMP study
- 3 year randomized masked clinical trial
- 116 children aged 8-11 years randomized to RGPs or soft lenses
- run in period to limit drop out
how does Orthokeratology work for myopia control?
- temporary reduction in myopia
- corneal reshaping, corneal refractive therapy, vision shaping treatment
- produced by flat-fitting rigid contact lenses
how does Ortho-K work?
- reverse geometry lens designs
- secondary curve steeper than base curve
- computer-assisted videokeratography
- highly gas permeable materials
- potential for overnight wear
ortho-K study (Cho et al. 2005) showed
corneal reshaping 0.29 +/- 0.27mm
spectacle wearers 0.54 =/- 0.27mm
(46% effect size)
ortho-K study (Walline et al. 2009) showed
56% effect size
in 1997, the “accommodative lag theory” mechanism for myopia and control stated that:
- under-accommodation during near work
- image focused behind retina at fovea
- relative hyperopia stimulates eye growth
- treat with plus at near: bifocals, PALs
in 2017, the “peripheral refraction theory” mechanism for myopia and control stated that:
- shorter off-axis eye length
- image focused behind retina in periphery
- relative hyperopia stimulates eye growth
- treat with plus in periphery
why do we care about peripheral refractive errors?
- refractive development regulated by visual feedback
- fovea not essential for vision-dependent growth
- when conflicting signals exist peripheral signals can dominate central
- peripheral optical errors can alter central refractive development
what are some clinical methods for putting plus in the periphery?
- corneal reshaping with ortho-k
- contact lenses with small optical zone
- spectacle lenses with add in all meridians
what study showed how contact lenses with small optical zone worked? what were the results?
- results from Brien Holden Vision Institute
- 34% reduction in progression of myopia relative to spectacle comparison group
- 33% reduction in axial elongation
what study showed how spectacle lenses with add in all meridians worked? what were the results?
- results from Brien Holden Vision Institute
- 15% reduction in progression compared to control group
- 30% reduction in younger children with at least one myopic parent
