The aim of this study is to analyse the effect of dehydration of two contact lenses – LC - (daily replacement hydrogel - Hioxifilcon A and monthly replacement silicone-hydrogel - Asmofilcon A) on their optical properties (transmittance, absorption and dispersion). Significant differences were found between dehydration levels of Hioxifilcon A and Asmofilcon A contact lenses. Conventional hydrogel lenses dehydrate quickly, which leads to a greater alteration of their optical properties. For both materials, with dehydration reflectance increases due to scattering within the material and transmittance decreases due to increased absorption. These changes are more noticeable for daily LCs of conventional hydrogel.
The aim of this study is to benchmark the optical properties (transmittance, absorption and dispersion) of two different types of contact lenses (daily replacement hydrogel - Hioxifilcon A and monthly replacement silicone-hydrogel - Asmofilcon A) in the visible spectra using the IAD method. Lower transmittance, lower absorption and higher dispersion were found for daily replacement contact lenses - Hioxifilcon A - than for monthly replacement contact lenses - Asmofilcon A. As diopter powers increase for both type of lenses, transmittance and absorption decrease and dispersion increases, which may have implications on the visual performance of these contact lenses.
The optical properties of a tissue or a biomaterial can be described in terms of the absorption coefficient (μa), the scattering coefficient (μs), the scattering function p(θ,ψ) and the real refractive index of the biomaterial. The Inverse Adding-Doubling, IAD, Method and relationship between the Kubelka- Munk parameters and the transport coefficients are used to describe optical properties at different wavelengths for a large variety of tissues and tissue like biomaterials, such as native cornea, tissue engineered cornea, tissue engineered oral mucosa, natural dentin and dental resin nanocomposites, among others
Optical properties of experimental graphene dental nanocomposites were studied. Spectral reflectance was measured and S and K coefficients as well as transmittance of samples were calculated using Kubelka-Munk’s equations. The spectral behavior of S, K and T experimental graphene exhibited different trends compared with the commercial nanocomposites and they were statistically different. Experimental nanocomposites show higher scattering and lower transmittance when compared with commercial nanocomposite, probably, due to the shape, type and size of the filler. K for short wavelength of the pre-polymerized experimental nancomposites was very low. According to our results, hidroxypatite with graphene oxide used in dental nanocomposites needs to be improved to reproduce esthetic properties of natural dental tissues and to have potentially clinical applications.
The optical evaluation carried out using the Inverse Adding-Doubling (IAD) method to determine the scattering and the absorption coefficients of the bioengineered human corneal stromas showed that this type of artificial biomaterials shared many similarities with native control cornea after four weeks of development in culture. Their absorption and reduced scattering coefficients values were higher than the ones of the control cornea, but their spectral behaviors of both coefficients were similar. Time of development in culture was an influencing factor on the results.
In teaching of Vision Physics or Physiological Optics, the knowledge and analysis of the aberration that the human eye presents are of great interest, since this information allows a proper evaluation of the quality of the retinal image. The objective of the present work is that the students acquire the required competencies which will allow them to evaluate the optical quality of the human visual system for emmetropic and ammetropic eye, both with and without the optical compensation. For this purpose, an optical system corresponding to the Navarro-Escudero eye model, which allows calculating and evaluating the aberration of this eye model in different ammetropic conditions, was developed employing the OSLO LT software. The optical quality of the visual system will be assessed through determinations of the third and fifth order aberration coefficients, the impact diagram, wavefront analysis, calculation of the Point Spread Function and the Modulation Transfer Function for ammetropic individuals, with myopia or hyperopia, both with or without the optical compensation. This course is expected to be of great interest for student of Optics and Optometry Sciences, last courses of Physics or medical sciences related with human vision.
Understanding the behaviour of light propagation in biological materials is essential for biomedical engineering and its
applications. Among the key optical properties of biological media is the angular distribution of the scattered light,
characterized by the average cosine of the scattering angle, called the scattering anisotropy coefficient (g). The value of g
can be determined by experimentally irradiating the material with a laser beam and making angular-scattering
measurements in a goniometer. In this work, an experimental technique was used to determine g by means of
goniometric measurements of the laser light scattered off two different dental-resin composites (classified as nano and
hybrid). To assess the accuracy of the experimental method, a Mie theory-based computational model was used.
Independent measurements were used to determine some of the required input parameters for computation of the
theoretical model. The g values estimated with the computational method (nano-filled: 0.9399; hybrid: 0.8975) and the
values calculated with the experimental method presented (nano-filled: 0.98297 ± 0.00021; hybrid: 0.95429 ± 0.00014)
agreed well for both dental resins, with slightly higher experimental values. The higher experimental values may indicate
that the scattering particle causes more narrow-angle scattering than does a perfect sphere of equal volume, assuming
that with more spherical scattering particles the scattering anisotropy coefficient increases. Since g represents the angular
distribution of the scattered light, values provided by both the experimental and the computational methods show a
strongly forward-directed scattering in the dental resins studied, more pronounced in the nano-filled composite than in
the hybrid composite.
Photocured polymers are widely used in dental applications. The optical properties of the dental composites change
during curing; the appearance of the composites also changes. Recently, a new silorane-based composite resin and dental
nanocomposite have been introduced. However, research regarding the effect of the silorane monomers or the size filler
on appearance after curing of the resin composite is limited. This work aims to examine the optical properties of
silorane-based composite and nanocomposite, in terms of scattering and absorption during curing.
Six dimethacrylate-based dental resin composite (five universal and one nanocomposite) and one silorane-based dental
resin composite (all shades A2 and T) were studied. The curing irradiance was 1100mW/cm2. The spectral reflectance of
1mm thick composite samples against white and black backgrounds were measured both before and after curing, and
were converted to scattering and absorption coefficients using the Kubelka-Munk Theory.
Both for pre and post-curing dental resin composites, the Albedo coefficient (K/S) shows that absorption prevails over
the scattering for short wavelengths while for medium and large wavelengths, the scattering becomes more important,
except for the T shade of the nanocomposite. After curing, the scattering and absorption values decreased for both types
of materials. Changes in the absorption coefficient values should be caused by changes in the camphorquinone (CQ)
absorption, whereas the scattering changes found should be directly attributable to index of refraction changes of the
resin during curing.
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