Visual simulation of different optical designs

Resumo

Presbyopia is the age-related, irreversible loss of the accomodative ability of the human eye, which affects near visual performance. The present PhD Thesis aimed to evaluate optical and visual aspects of multifocal designs for presbyopia treatment that can be found in contact and intraocular lenses. First, a metric was implemented that facilitates the in vitro evaluation of intraocular lenses. The idea of the metric is based on the axial modulation transfer function of the intraocular lenses which can be obtained with a proper laboratory equipment. The metric assesses the volume under the surface defined by the axial modulation transfer function within adjustable defocus and spatial frequency intervals. It allows for fast and objective comparisons between different types and designs of intraocular lenses, therefore, it can be a useful tool in laboratory evaluation of presbyopic optical elements. The metric was applied for evaluating the in vitro optical quality of four different types of intraocular lenses that consisted of the most common designs: a monofocal, a bifocal, a trifocal and an extended range intraocular lens, revealing the optical quality that these elements can offer according to their design. The evaluation was performed for two different pupil diameters (3-mm and 4.5-mm) and the results suggested that the optical quality of the monofocal design for far vision was superior than that exhibited by the multifocal designs. On the other hand, the multifocal intraocular lenses provided better optical quality at more than one vergence. Since some pseudophakic patients implanted with multifocal intraocular lenses show elevated straylight levels, the abovementioned lenses were tested with an apparatus for assesing in vitro their straylight levels; the results showed no differences between the monofocal and the multifocal designs. Moreover, the straylight levels of all the lenses were lower than the straylight exhibited by the young healthy crystalline lens. For multifocal contact lenses the pupil dynamics have a crucial role in the visual performance. For this purpose, the power profiles of center-near and center-distance designs were obtained and a thorough analysis of the effect of pupil size upon the power distribution of these lenses was performed. The results of this study, if combined with pupil data from presbyopes, can provide useful information for improving the fitting of presbyopes, thus increasing visual performance with multifocal contact lenses. Since simultaneous vision is the most common approach for multifocal solutions, a methodology for non-invasive control of visual performance with simultaneous vision solutions was presented. This methodology is based on adaptive optics technology and the ability of a deformable mirror to change its shape in a quick fashion between two vergences (temporal multiplexing). It can simulate different bifocal designs, including toric and combinations of spherical aberration and investigate subjective visual performance for different multifocal contact or intraocular lens designs. Lastly, a pilot study was conducted where high (100%) and low contrast (10%) visual acuity with simulated optical designs was evaluated by obtaining defocus curves. The simulations were generated using Fourier optics and included a monofocal, an angular bifocal, a radial bifocal, a radial trifocal and an extented range design. To those simulations, higher order aberrations from an aging cornea were added. The preliminary results showed that corneal higher order aberrations could increase the depth of focus in expense of visual acuity and also that low contrast visual acuity was worse with multifocal designs in particular.