Συσχετισμός δυναμικών ιδιοτήτων των οφθαλμικών ιστών και παθήσεων του οφθαλμού. Μη-επεμβατική διάγνωση με την χρήση τεχνικών σκέδασης φωτός laser

Abstract

On account of the transparency of ophthalmic tissues, light scattering is an ideal tool for detecting the early stages of some of their pathological conditions. For example, the opacity of the mammalian lens due to age or other external causes is called cataract. Cataract cannot be detected clinically at early stages and as a result serious vision problems appear. The fact that, light has the ability to detect molecular changes that are related to the mechanism of cataract formation draws attention to the importance of early diagnosis in ophthalmic disorders. The lens can be considered as a dense colloidal protein dispersion (crystallins, ~ 40% wt) in water where the opacity that leads to cataract formation how its basis to the aggregation of proteins. This dissertation is aimed at studying the molecular changes that take place upon cataract development. Particular emphasis is paid to the development of a non-invasive methodology for early diagnosis of ocular diseases with the aid of dynamic light scattering. By means of this technique, suitably modified for the study of ophthalmic tissues, the dynamic properties of the proteins of porcine lenses (e.g. diffusion coefficients and their temperature dependence at various parts inside the lens, etc.) were studied by using the experimental model of ‘cold’ cataract. In cold cataract the controlled cooling of the lens at temperatures below the physiological one induces gradual cataractogenesis. In particular, we focused on four kinds of experiments. (a) Detailed study on the cold cataract onset in the lens nucleus. (b) Study on the effect of the laser light wavelength in the onset and the extent development of cold cataract. (c) Study of the cold cataract effect along an equatorial diameter of the lens, considering the gradual concentration of the lens proteins (high protein concentration in the nucleus and low concentration in the cortex). (d) Study on the effect of thermal history, i.e. by warming up the lens at temperatures higher than the physiological one on the cold cataract effect. The basic conclusions of the present dissertation are summarized as follows: There are clear correlations between the spectral characteristics (autocorrelation functions) and the hierarchical stages of the onset of cataract. Qualitative and quantitative changes in the temperature dependence of several parameters, which are related with the diffusive motions of proteins at the early stages of cataract, appear already at 17 oC while the nucleus is still clear and highly transparent. The use of laser radiation close to the ultraviolet part of the spectrum seems to enhance the formation of cold cataract in the lens nucleus. Cold cataract does not develop at the cortex of the lens, in view of the low protein concentration. The lens pre-heating at a certain temperature for various time periods affects significantly cold cataract formation in the lens nucleus but not in lens cortex. The above mentioned make clear that dynamic light scattering can indeed provide useful parameters that can be successfully used as sensitive and reliable indicators for the early, non-invasive diagnosis of cataract in mammalian lenses and in vivo.