PhD Thesis Defenses

Myopia control and peripheral vision

The rapid rise in myopia prevalence has caused an urgent need for effectivemyopia control interventions. This thesis investigates the role of theperipheral optics of the human eye in myopia progression. It was initiallybelieved that the axial elongation of the myopic eye is caused only by thedefocus signals presented to the central retina. However, studies on animals have proven that ocular growth can be regulated by optical factors beyondthe fovea. A common hypothesis nowadays is that peripheral image quality is an important factor for eye growth regulation also in humans. The detection of the sign of defocus by the retina is essential for the control of both accommodation and eye growth. Therefore, the aim of this thesis is to map out visual cues to myopia development by evaluating peripheral vision. Additionally, effective optical properties of multifocal contact lensesfor myopia control have been investigated.

Peripheral vision was evaluated by adaptive psychophysical routines inorder to find properties in the peripheral image quality that might be used by the eye to detect the sign of defocus. We have shown that peripheral high-contrast detection acuity and contrast sensitivity can be improved by correction of higher-order aberrations and eliminating chromatic aberrations.The measurements proved that asymmetries in peripheral vision under myopic and hypermetropic defocus are mainly due to the monochromatic and not the chromatic aberrations of the eye. Moreover, we found that relative peripheral refraction did not change with increasing accommodationfor emmetropes, whereas for myopes a myopic shift was observed.However, in spite of these differences, the two groups showed similar peripheral modulation transfer functions. When subjects were accommodating to an off-axis target, the accommodation amplitude declined and the accommodation response time increased with eccentricity. Finally, we evaluated optical quality and vision with the MiSight multifocal contact lens for myopia control. We believe that the effective optical properties of this lens are the larger peripheral blur and the more asymmetric point spread function,due to the additional astigmatism and coma, and that this leads to the larger accommodative response shown by some of the subjects.