Methods to measure intraocular scattering and its impact in vision

Resumo

Objectives An optical system, like the human eye can be characterized by its Point Spread Function (PSF), a function that describes the angular distribution of light, deriving from a point source and propagated through this specific optical system. Thus, the main objective of the thesis was to establish novel methods for the acquisition of the PSF of optical systems and their components. Methods A new method was established for the estimation of the PSF eliminating the need of detectors with high dynamic range. Initially, this methodology was applied to characterize the scattering that Intraocular lenses, materials and biological tissues, produce. The same methodology was applied for in-vivo scattering measurements of the human eye. In parallel, a new method to evaluate the effect of scattering on human vision, was developed. Additionally, a more intuitive version of this method was included in an application run by low cost mobile devices. Finally, the know-how the experience and the modalities gained form the previously mentioned methods, was applied on a prototype compact device for the measurement of the macular pigment, present on the human retina. Results The initial results, obtained by the developed novel method, for commercially available diffusers for the generation of scattering, were in accordance with the density, provided by the manufacturer and by previous studies. Moreover, the same methodology was used for the characterization of Intraocular Lenses (IOL's) by means of produced scattering. It was discovered that the differences in design and manufacturing process between mono- and multi-focal IOL's may lead to higher levels of produced scattering. Additionally, it was confirmed that corneal edema may result to increased intraocular scattering. The previously described method was applied on a double pass optical design which was applied to measure in-vivo, human eyes. The effect of the wavelength on ocular scattering was revealed through measurements using different wavelengths. The same methodology, previously developed on an optical table, was consecutively fitted in a compact prototype device, making its use in clinical sites, possible. The results from a small scale clinical study compared it effectiveness, repeatability and reliability comparing the prototype with other state of the art methods and devices for the evaluation of intraocular scattering. Additionally, a new differential method for the evaluation of Contrast sensitivity (CS) was developed. A new metric was compared to the S parameter (a parameter for the intraocular scattering measurement) obtained by two other different devices. The macular pigment optical density of several subjects was measured and evaluated by a new device. These results were also compared to other large scale studies previously documented. Conclusions A new method for the reconstruction of the PSF up to wide angles, was established. This method allowed the evaluation of scattering of optical systems and its components. The same method was successfully applied for the optical characterization of IOL's depending on their design and manufacturing process. Additionally, the relation between intraocular scattering and corneal edema was identified. The previously mentioned method was applied for the in-vivo measurement of human eyes. The correlation of intraocular scattering with the wavelength was also justified. The methodology was ported to a compact prototype device for the fast and precise measurement of ocular scattering applied on clinical sites. A new methodology for the measurement of the S parameter through the evaluation of CS was established. This differential method was implemented in a portable device (an iPad) whose advanced technological specifications made the evaluation of intraocular scattering possible, using low cost hardware. Finally, the methodology and the modalities applied for the measurement of intraocular scattering, were applied on another prototype device for the measurement of the macular pigment optical density.