Purpose: To study the impact of minus spectacle optics on peripheral refraction and choroidal thickness regardless of the shape of the eye by simulating bilateral myopia in emmetropes.
Methods: This study was a randomized balanced crossover design. 19 emmetropic subjects with the inclusion of individuals having a refractive power between +0.50 to -0.50Dioptre(D) were simulated as myopes using plus powered single vision contact lenses and were corrected with minus powered single vision spectacle lenses. The participants were randomized into wearing two different lens type combinations (-2D/+1.75D) and( -6D/+5.50D) on two different days and were measured for peripheral refraction and choroidal thickness pre and post-treatment.
Results: The minus spectacle lens showed a relative hyperopic RPR(relative peripheral refraction) regardless of the eye shape. The main effects for lens type(F = 19.181 p <0.001), condition (F = 26.476 p<0.001) and angle(F = 13.368 p<0.001) were statistically significant. The RPR relatively became more hyperopic with an increase in power of the spectacle lens. The CT(choroidal thickness) was not found to be significant pre and post-treatment (F =.832 p = .362), but the trends observed in the participants showed subtle thinning consistently among each subject due to the defocus.
Conclusions: The minus spectacle lens creates some amount of relative hyperopic RPR regardless of the eye shape. The optics of the traditional spectacle design is not controlling but contributing to myopia progression. The relative hyperopic defocus is not only created by the shape of the eye, but it is also due to the minus spectacle optics.
Keywords: myopia progression, minus spectacle, peripheral refraction, choroidal thickness, relative hyperopic defocus.
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