Paolo Sirotti

Analysis of light energy distribution by multifocal intraocular lenses through an experimental optical model

Purpose: To analyze and compare the light energy distribution generated by multifocal intraocular lenses (IOLs). Setting: Laser Laboratory of the Department of Electronics, Electrotechnics and Informatics, University of Trieste, Italy. Methods: An optic system to examine the division of a laser beam in the various focal spots of multifocal IOLs was developed. The model consists of a helium‐neon laser and an optical system: a triangular optical bench with a precision collimator, a micropositionable immersion stage supporting the IOL to be measured, and a digital image‐processing system. Four bifocal and three multifocal IOLs were studied. This system is able to expand the distance between foci, leading to a sharper separation of the focal spots. The resolution of the images makes it possible to analyze the distribution of total light energy among the foci. Results: Results showed the variation in light intensity of the focal spots of multifocal and bifocal IOLs, as well as their disposition in the dioptric range. Conclusion: Light distribution among various focal distances corresponded to the foci provided by monofocal, bifocal, and multifocal IOLs. The percentage of light energy distribution was related to the importance of each focus.

Visualization of fluid turbulence and acoustic cavitation during phacoemulsification

Purpose: To describe a technique for visualizing fluid turbulence and cavitational energy created by ultrasonic phaco tips. Setting: University Eye Clinic of Trieste, Trieste, Italy. Methods: Generation of cavitational energy by the phaco tip was visualized using an optical test bench comprising several components. The technique uses a telescope system to expand a laser light source into a coherent, collimated beam of light with a diameter of approximately 50.0 mm. The expanded laser beam shines on the test tube containing the tip activated in a medium of water or ophthalmic viscosurgical device (OVD). Two precision optical collimators complete the optical test bench and form the system used to focus data onto a charge‐coupled device television camera connected to a recorder. Results: Images of irrigation, irrigation combined with aspiration, irrigation/aspiration, and phacosonication were obtained with the tip immersed in a tube containing water or OVD. Conclusions: Optical image processing enabled acoustic cavitation to be visualized during phacosonication. The system is a possible means of evaluating a single phaco apparatus power setting and comparing phaco machines and techniques.

Phase image visualization with white light extended sources: a Fourier-optics-based interpretation

Focusing schlieren with white light extended sources, an optical processing technique used to visualize phase images, is mathematically formalized in terms of Fourier optics and therefore classified as a typical procedure of optical image processing. The visualization is obtained by completely or partially stopping the image of the light source. In these two situations, the relation between the resulting image intensity and the phase that must be visualized is described by different equations. In the first case, the result is similar to that obtainable by the strioscopy (dark-field technique) operated in coherent optics; in the second case, the result resembles that of the coherent schlieren. The mathematical treatment is carried out using an extended white light source codified by a grid: the filter is the negative of the source grid image, centered or shifted with respect to the image itself. Experimental phase images are visualized by means of the codified source and by an incandescent bulb.

A Hybrid Computer for Phase Images Visualization and Correlation Based Recognition

We examine some possibilities of an optical-digital hybrid computer for the processing of phase images constituted of surfaces or transparent thin materials. Different modalities of operation are possible, depending on the stage of the process in which it is more convenient to turn from optical to digital operation and on the objective of the process. Two subjects are treated: first a phase image is visualized employing a rotating derivative filter, secondly we survey some applications of a correlation based recognition method to surface textures and to mechanical or thermal stresses in thin transparent materials.

Optical Processing of Linear Array Ultrasonic Images

Recent advances in dynamic scanners resulted in construction of high resolution linear array transducers that have rapidly become the most popular instruments in ultrasound examination. Nevertheless the apparent resolution of the resulting scans is degraded due to the structure of the displayed image which is formed by separated scan lines. In this paper we propose a new system of optical processing which allows both to enhance the effective resolution and to suppress the raster.

Coherent Optical Analysis, Filtering And Correlation Of Reflected Images

A reflected image can constitute the input image for a coherent optical processing system. We have set up an optical-digital hybrid computer which in its optical part uses two distinct lasers, one to process transparent images, the other to process reflected images. As examples of achievable operations two kinds of processes are illustrated: in the first one a reflected image is optically filtered with a continuously varying filter obtained with the technique of rotating filters. In the second one a pattern recognition method, the joint Fourier transform (JFT) correlation, is applied to both stationary and time varying surface textures.

Experimental setup and methodology for automatic quality assessment of intraocular lenses

Intraocular lenses (IOLs) are widely used in cataract surgery. There is a variety of IOLs depending on lens material, optical and mechanical design. Evaluation of the visual performance obtainable with intraocular lenses is important for objective comparison between IOL models. Indeed, the visual performance of implanted lenses has a deep impact on the life of the subjects, having medical, social and economical consequences. The purpose of the present paper is twofold: first, we propose an experimental setup, consisting of an actuated opto-electro-mechanical eye capable of simulating different refractive and optical conditions. Second, we suggest to employ some well-known image quality assessment tools for evaluating the visual performance of different IOLs (or of the same IOL in different conditions) based on the comparison between the original image and that produced by the artificial eye equipped with the IOL. The objective and repeatable results obtained, are in accordance with subjective evaluation (a time-consuming procedure employed in previous works).

Schlieren visualization of fluid dynamics phenomena during phacosonication in cataract surgery

In ultrasonic phacoemulsification during cataract surgery the lens material fragmentation has been described as being caused by a combination of several mechanisms. The different theories involve tip vibration, acoustic waves produced by the tip, particles and liquids impact on the surface of the lens and cavitation. However the mechanisms are still not clear. To better understand phaco-related phenomena we have tried to produce a description in term of images of the cataract phacoemulsification procedure. An expanded and collimated laser diode beam transilluminates a transparent tube containing a liquid medium. The machine is activated separating the different phases of irrigation, aspiration and phacosonication. Fluid turbulences and phenomena related to the tip vibration constitute the phase images, visualized using Schlieren or similar techniques. The optical Fourier transform is filtered by a blade or by a black dot. The filtered transform is reconstructed into the visualized phase image and this is acquired by a digital image processing system. The presence of acoustic cavitation and possibly of ultrasonic radiation has been revealed. The technique promises to be a possible means for evaluation of single phaco apparatus power setting and comparison between different machines in terms of power modulation and cavitation production.

Coherent Optical Correlation For Defocused Images Recognition

Deblurring images affected by severe focus defeat gives often poor results. A coherent optical method, the joint Fourier transform correlation, is suggested for the recognition of defocused images. Basing on the symmetry of the crosscorrelation function between an out-of-focus and the in-focus image, the recognition may be attempted simply correlating the unknown out-of-focus image with a set of reference in-focus images.

Joint Fourier Transform Cross-Correlation for Liver Echotexture Classification

Tissue characterization of liver echographic scans was obtained using an optical-digital procedure of direct correlation between the unknown texture and a set of reference textures.