PURPOSE. To evaluate light scatter and stray light in intraocular lenses (IOLs) explanted because of postoperative opacification (13 calcified hydrophilic acrylic, 1 calcified silicone, and 4 polymethylmethacrylate [PMMA] lenses with snowflake degeneration), as well as effect of opacification on other optical quality/performance indicators, in comparison with controls. METHODS. The Complete Angle Scatter Instrument (CASI) scatterometer was used to measure the forward light scattering (FLS) of the IOLs, and the stray light values at various angles were calculated from the measured FLS. Modulation transfer function (MTF) was obtained with an optical bench, and a Badal optometer was used to obtain letter chart images through the lenses. Back light scatter and light transmittance were also measured. RESULTS. Average stray light values (Log (s)) at a scattered angle of 100 were 1.79 +/- 0.37 for hydrophilic acrylic IOLs (controls 0.36 +/- 0.05), 1.53 for the silicone lens (control 0.41), and 1.62 +/- 0.46 for PMMA IOLs (control 0.25). Stray light was significantly higher for explanted opacified lenses (N = 18) in comparison with controls (N = 7; two-tail P < 0.001 at 100). Modulation transfer function and Badal image contrast were drastically reduced in lenses with calcification and snowflake degeneration. CONCLUSIONS. Different studies described the impact of stray light in human vision, with serious hindrance above 1.47 Log (s). Lenses explanted from patients because of clinically significant opacification are associated with a considerable increase in light scatter and stray light, as well as with a decline of other optical quality/performance indicators.

Purpose: 1) To estimate the threshold dose and the time evolution for cataract induction by near infrared radiation (IRR) in seconds exposure time domain; 2) to determine the ocular temperature development during the threshold exposure; 3) to investigate if near IRR induces cumulative lens damage considering irradiance exposure time reciprocity; 4) to experimentally estimate the temperature in the lens indirectly from the measurement of temperature-induced light scattering increase. Methods: Before exposure, 6-weeks-old albino rats were anesthetized and the pupils of both eyes were dilated. Then the animals were unilaterally exposed to 1090 nm IRR within the pupil area. Temperature was recorded with thermocouples placed in the selected positions of the eye. At the planned post-exposure time, the animal was sacrificed and the lenses were extracted for measurements of forward light scattering and macroscopic imaging (Paper I-III). In Paper IV, the lens was extracted from six-weeks-old albino Sprague-Dawley female rats and put into a temperature-controlled cuvette filled with balanced salt solution. Altogether, 80 lenses were equally divided on four temperature groups, 37, 40, 43 and 46 ºC. Each lens was exposed for 5 minutes to temperature depending on group belonging while the intensity of forward light scattering was recorded. Results: The in vivo exposure to 197 W/cm2 1090 nm IRR required a minimum 8 s for cataract induction. There was approximately 16 h delay between exposure and light scattering development in the lens. The same radiant exposure was found to cause a temperature increase of 10 °C at the limbus and 26 °C close to the retina. The in vivo exposure to 96 W/cm2 1090 nm IRR with exposure time up to 1 h resulted in an average temperature elevation of 7 °C at the limbus with the cornea humidified and no significant light scattering was induced one week after exposure. Arrhenius equation implies that the natural logarithm of the inclination coefficient for light scattering increase is linearly dependent on the inverse of the temperature. The proportionality constant and the intercept, estimated as CI(0.95)s, were 9.6±2.4 x103 K and 22.8±7.7. Further, it implies that if averaging 20 measurements of inclination coefficients in a new experiment at constant heat load, the confidence limits for prediction of temperature correspond to ±1.9 °C. Conclusions: It is indicated that IRR at 1090 nm produces thermal but not cumulatively photochemical cataract, probably by indirect heat conduction from absorption in tissues surrounding the lens. Applying the Arrhenius equation the in vivo temperature in the lens can be determined retrospectively with sufficient resolution.

Σκοπός της διδακτορικής διατριβής είναι η ανάπτυξη κατάλληλων μεθόδων ψηφιακής επεξεργασίας εικόνας και αναγνώρισης προτύπων με τις οποίες θα προσδιορίζονται βιομετρικές και διαγνωστικές παράμετροι μέσω της αλληλεπίδρασης φωτονίων στο ορατό και υπέρυθρο φάσμα. Πιο συγκεκριμένα επιλύεται ένα αντίστροφο πρόβλημα σκέδασης ΗΜ ακτινοβολίας από ένα ανθρώπινο, υγιές και απαραμόρφωτο ερυθρό αιμοσφαίριο. Παρουσιάζονται μέθοδοι εκτίμησης και αναγνώρισης των γεωμετρικών χαρακτηριστικών απαραμόρφωτων υγιών ερυθρών αιμοσφαιρίων με χρήση εικόνων που προσομοιώνουν φαινόμενα σκέδασης ηλεκτρομαγνητικής ακτινοβολίας που διέρχεται από προσανατολισμένα ερυθρά αιμοσφαίρια. Η διαδικασία της ανάκτησης της πληροφορίας περιλαμβάνει, εξαγωγή χαρακτηριστικών με χρήση δισδιάστατων μετασχηματισμών, κανονικοποίηση των χαρακτηριστικών και την χρήση νευρωνικών δικτύων για την εκτίμηση των γεωμετρικών ιδιοτήτων του ερυθροκυττάρου. Παράλληλα σχεδιάστηκε και αξιολογήθηκε σύστημα αναγνώρισης των γεωμετρικών χαρακτηριστικών των ερυθρών αιμοσφαιρίων. Οι εικόνες σκέδασης δημιουργήθηκαν προσομοιώνοντας το πρόβλημα εμπρόσθιας σκέδασης ενός επίπεδου ηλεκτρομαγνητικού (ΗΜ) κύματος, χρησιμοποιώντας την μέθοδο των συνοριακών στοιχείων, λαμβάνοντας υπόψη τόσο την αξονοσυμμετρική γεωμετρία του ερυθροκυττάρου όσο και τις μη αξονοσυμμετρικές οριακές συνθήκες του προβλήματος. Η επίλυση του εν λόγω προβλήματος πραγματοποιήθηκε στα 632.8 nm και εν συνεχεία επεκτάθηκε σε 12 διακριτά ίσου βήματος μήκη κύματος από 432.8 nm έως 1032.8 nm. Επίσης, προτάθηκε μία νέα πειραματική διάταξη για την απόκτηση πολλαπλών εικόνων σκέδασης και την εκτίμηση των γεωμετρικών χαρακτηριστικών των ερυθρών αιμοσφαιρίων, αποτελούμενη από μία πολυχρωματική πηγή φωτός (Led) και πολλαπλά χρωματικά φίλτρα. Επίσης κατασκευάστηκε μέθοδος επίλυσης του σημαντικού προβλήματος εύρεσης της περιεκτικότητας του διαλύματος σε ερυθρά αιμοσφαίρια διαφορετικών μεγεθών στην περίπτωση απόκτησης πολλαπλών εικόνων σκέδασης από διαφορετικές φωτοδιόδους και πολλαπλά χρωματικά φίλτρα. Στα πειράματα αξιολόγησης της μεθόδου που προτείνεται με εικόνες προσομοίωσης δείχνεται ότι είναι ικανή η εύρεση της αναλογίας των ερυθρών αιμοσφαιρίων με πολύ μεγάλη ακρίβεια ακόμα και στη περίπτωση όπου στις εικόνες έχει προστεθεί λευκός κανονικός θόρυβος. Η βασική μεθοδολογία που παρουσιάζεται στην παρούσα δια-τριβή μπορεί να χρησιμοποιηθεί για την αναγνώριση παθολογικών αιμοσφαιρίων ή να χρησιμοποιηθεί στην αναγνώριση μικροσωματιδίων σε υγρά ή αέρια. / The aim of this PhD thesis is the development of digital image processing and pattern recognition methods to estimate biometric and diagnostic parameters using scattering phenomena in the visible and infrared spectrum. More concretely, several reverse scattering problems of EM radiation from a human, healthy and undistorted Red Blood Cell (RBC) is solved. Methods of estimation and recognition of geometrical characteristics of healthy and undistorted RBCs using simulating images are presented. The information retrieval process includes, features extraction using two-dimensional integral transforms, features normalization, and Neural Networks for estimation of three major RBC geometrical proper-ties. Using the same features set, a recognition system of the geometric characteristics of RBCs was developed and evaluated. The scattering images were created simulating the forward scattering problem of a plane electromagnetic wave using the Boundary Element Method, taking into account both axisymmetric geometry of the scatterer and the non-axisymmetric boundary conditions of the problem. Initially, the problem is solved at 632.8 nm and consequently the same problem was solved at 12 different wavelengths, from 432.8 to 1032.8 nm equally spaced. Also, a new device for acquisition of scattering images from RBCs-flow, consisting of a multi-color light source (Led) was proposed, for RBC size estimation and recognition. Finally, a system for the estimation of different RBCs concentration was developed when scattering images acquired using multiple scattering images acquired from multiple Leds and color filters. The system was evaluated using additive white regular noise.