Oblique effects with multisegment spectacle lenses: 1. Images of a point object.

Introduction: Multisegment (MS) spectacles are intended to slow myopia progression by modifying images falling on the peripheral retina. Some published optical treatments of these lenses assume normal incidence of light at the surfaces, but images falling on the peripheral retina are usually associated with oblique ray pencils. Here, we model representative images of point objects produced by the Hoya MiyoSmart MS spectacle lens when oblique ray pencils are used.

Methods: Various imaging aspects of the MS lens alone and in combination with a suitable accommodating eye model for a 4D myope were evaluated using the Optical Design program Ansys Zemax OpticStudio. Configurations studied included object points at vergences of zero and -4 D, with the objects being either on the lens axis or at a field angle of about 30°. The effect on foveal vision of rotating the axis of the eye with respect to that of the lens was also considered. Images of point objects were described in terms of spot diagrams and fast Fourier transform point-spread functions.

Results: Symmetry and overall optical quality of images decreased with the obliquity of the ray pencils, due to the increased off-axis aberrations of the lens and the eye. Images of near object points were strongly affected by the level of accommodation: optimal retinal image quality occurred when accommodation brought the carrier lens focus close to the retina, rather than that of the lenslets.

Conclusions: Attempts to understand why MS lenses slow myopia progression need to consider the way in which through-focus retinal image quality changes with obliquity of the ray pencils across the visual field and the possible effects of ocular accommodation.