Abstract:
Myopia, characterized by an excessively long axial eye length or an overly strong refractive power, has emerged as a global public health concern. From an individual perspective, uncorrected myopic refractive errors can reduce the quality of life and increase the risk of developing sight-threatening eye diseases, especially in high myopia. Furthermore, from a societal view, myopia prevalence is increasing worldwide, raising the need to counteract progressive myopia. Therefore, myopia and its associated complications are a high priority for research.
Current myopia management is based on environmental, behavioral, pharmacological, and optical control strategies. This dissertation seeks to understand the underlying mechanisms of an optical myopia control strategy that utilizes scattering, which induces image contrast reduction. Although a clinical trial of this approach has shown promising results, the mechanisms behind the strategy and its effectiveness remain unclear. Therefore, this dissertation examines short-term adaptation to scattering on contrast sensitivity, neural contrast sensitivity, choroidal thickness, axial length, and visual acuity. These short-term effects indicate a hint of long-term changes, which would be decisive for controlling progressive myopia.
In the first study, it was investigated how short-term exposure to peripherally induced scattering (Bangerter foil 0.4 and 0.8) affected central chromatic and achromatic contrast sensitivity. No contrast adaptation, defined by an increase in supra-threshold contrast sensitivity, was observed after exposure to both levels of peripherally induced scatter. Instead, there was a reduction in contrast sensitivity after 90 minutes of exposure to Bangerter foil 0.8. In the second study, it was tested how 30 minutes of adaptation to full-field scattering (Bangerter foil 0.8) determined neural contrast sensitivity and compared it with imposed positive defocus of +0.5 diopter. The dioptric power of defocus was matched to the scattering condition by a visual acuity reduction of 0.1 logarithm of the minimal angle of resolution. Neural contrast adaptation was found only for the scattering condition but not for defocus. Finally, the effects of peripheral and full-field scattering using sandblasted lenses of medium and high levels on choroidal thickness, axial length, and visual acuity were measured. Choroidal thickening was found after 60 minutes of adaptation to medium peripheral scattering, most pronounced in the superior peripheral retina, and to medium full-field scattering in the nasal central retina. Axial length and visual acuity were not affected by any of the scattering conditions.
The study results provide new insights into short-term adaptation to optically induced scattering on contrast sensitivity, choroidal thickness, axial length, and visual acuity. In the second and third studies, contrast adaptation was observed; however, not in the first study. Contrast adaptation effects would be sensitive enough to provide a signal for eye growth and therefore, refractive development, which could be useful in controlling myopia.
contrast modulation