[Study of the structure of contact lenses using PALS, MIR and Raman spectroscopy in the regard of safety of persons exposed to ionizing radiation].

Among patients and health professionals who are exposed to ionizing radiation during diagnostic and therapeutic procedures, refractive errors are common and soft contact lenses are widely used to correct them. Changes in the inner structure of contact lens may influence the safety of its usage through modification of its water content or oxygen accessibility to cornea. Therefore, analysis of impact of external factors, therein ionizing radiation used in medicine, on contact lenses parameters is necessary, particularly to compare the presence of free volume gaps in the structure of the polymer soft contact lenses. Possible change in dimensions or quantity of free volume gaps in the structure of the material caused by the exposure to ionizing radiation may have negative influence on oxygen permeability. To prevent such process, different means could be used, i.a., positron annihilation lifetime spectroscopy (PALS), Raman spectroscopy and mid-infrared spectroscopy (MIR). Use of contact lenses which reduce transport of oxygen to cornea increases the risk of corneal hypoxia - one of the possible complications of using contact lenses. Research on effects of different types of ionizing radiation (X-ray, gamma, beta) on materials used in production of contact lenses is vital because of the connection of this issue with the safety of contact lenses wearers. Such research can also shed light on the problem of safe use of contact lenses by persons exposed to ionizing radiation.

A study of the effect of X-ray irradiation on the structure of Narafilcon A biopolymer soft contact lenses.

BACKGROUND: The effects of external factors such as X-ray irradiation on the structure and physical properties of contact lenses are very important for both the patients using contact lenses and medical personnel. OBJECTIVES: The aim of the study was to investigate the effect of X-rays on the structure of Narafilcon A silicone-hydrogel contact lenses. MATERIAL AND METHODS: In order to study the structural changes caused by X-rays in Narafilcon A polymer contact lenses, the following spectroscopy methods were used: positron annihilation lifetime spectroscopy (PALS), Fourier transform middle infrared spectroscopy (FTIR) and Raman spectroscopy (RS). Irradiation of the investigated sample was carried out using an Elekta Synergy accelerator. The contact lenses were irradiated with the following total doses of X-rays: 0.05 Gy, 0.5 Gy, 0.8 Gy, and 1.0 Gy. RESULTS: The PALS measurements showed that X-ray irradiation caused slight changes in the size of the free volume and the fractional free volume in the structure of the polymer contact lenses examined. However, the FTIR and RS measurements showed that X-rays did not break the monomer bonds in the polymeric structure of the sample. CONCLUSIONS: The changes revealed by the PALS method may be related to possible displacement of monomer chains, resulting in changes in the dimensions and numbers of free volumes. The finding that X-ray radiation does not affect or damage polymer bonds can in the future contribute to the use of X-ray and gamma radiation to sterilize contact lenses.

Comparison of Occurrence of Free Volumes for Rigid Gas Permeable and Soft Contact Lenses.

BACKGROUND: The polymeric materials: hydrogel, silicone--hydrogel and methacrylic acid are used in ophthalmology for the manufacture of contact lenses. It is important to research the structure of these materials, mainly the prevalence of free volumes. OBJECTIVES: The study has been conducted in order to comparison the presence of free volume gaps in the structure of the polymer soft contact lenses: Etafilcon A (hydrogel), Narafilcon A (silicone-hydrogel) and the polymer rigid gas permeable (RGP) contact lens (Fluor-Silicon-Methacrylat-Copolymer). In addition, to demonstrate differences in the occurrence of free volumes between types of represented contact lenses. MATERIAL AND METHODS: Three types of polymer contact lenses were used as materials: Etafilcon A, Narafilcon A and Fluor-Silicon-Methacrylat-Copolymer. The study was done by means of positron annihilation lifetime spectroscopy (PALS). RESULTS: As a result of the performed measurements, a graphical curve resulted which describes the relationship between the number of the annihilation acts in the time function. Significant changes were observed in the ortho-positronium long life component τ3 and their intensities between the examined polymer contact lenses. CONCLUSIONS: The conducted study using the Tao-Eldrup model indicates the presence of free volume holes in all research materials. There is a clear difference in the free volume sizes and their fractions between measured contact lenses are connected with oxygen permeability in these lenses. The results lead to the following connection: contact lenses of higher oxygen permeability coefficients and a water content of less, have more and larger free volumes than contact lenses of less oxygen permeability coefficient.