purpose: to determine the prevalence of uncorrected refractive errors and its determinants in tehran in 2002. methods: a total of 6497 citizens representing a cross-section of the population of tehran were sampled using a stratified random cluster sampling strategy. of these, 4565 (70.3%) subjects participated in the study and were transferred to a clinic for an extensive eye examination and in...

purpose: to determine the prevalence of refractive errors and rate of need for spectacles in students of region one in mashhad, 2006. methods: by randomized cluster sampling, 2510 students were selected and underwent eye exami-nations including refraction (cycloplegic, manifest), visual acuity, cover test and determination of the spectacle prescription as well as best corrected visual acuity. e...

background: welding emits harmful rays to the eyes. we evaluate and compare the uv, blue light and ir transmittance characteristics of some currently available welding safety protectors with ansi z87.1 criteria. materials and methods: three type of welding safety protectors (three of each type) have been evaluated for spectral transmittance. one-sample t-test was performed to establish is there...

bioactive glasses are silicate-based and can form a strong chemical bond with the tissues. these biomaterials are highly biocompatible and can form a hydroxyapatite layer when implanted in the body or soaked in the simulated body fluid. due to several disadvantages, conventional glass processing method including melting of glass components, is replaced by sol-gel method with a large number of b...

Diffusion is due to thermally activated atomic-scale random motion of particles (atoms, ions and molecules) in minerals, glasses, melts, fluids, and gases (Fig. 1). The random motion leads to a net flux when the concentration (more strictly speaking, the chemical potential) of a component is not uniform. Even though diffusion is a microscopic process, it can lead to macroscopic effects. For exa...

the monolithic oxynitride glasses in sio2-al2o3-b2o3 system were synthesized using sol-gel method. the porous, dried gels were heated in flowing ammonia for different times and varying temperatures. the nitrogen content of the oxynitride glasses was determined using an oxygen-nitrogen analyzer. the chemical bonding state and properties of glasses were investigated by means of fourier transform ...

in spite of rapid advances in keratorefractive surgery in recent decades, the most common method for refractive error correction throughout the world is glasses, the discovery of which is attributed to the persians. other advantages include protection of the eye against trauma and radiations, correction of phorias and tropias and cosmetic reasons. the purpose of this article is to describe and ...

Oxynitride glasses are found as grain boundary phases in silicon nitride ceramics. They are effectively alumino-silicate glasses in which nitrogen substitutes for oxygen in the glass network, and this causes increases in glass transition and softening temperatures, viscosities (by two to three orders of magnitude), elastic moduli and microhardness. Calcium silicate-based glasses containing fluo...

The structural and optical characterization of bulk GeO2-PbO glasses was the goal of this study. In this regard, six different (100-x)GeO2‌-xPbO (15<x<45) glasses were prepared by conventional melt quenching technique between two steel sheets. The produced samples were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and UV-Vis s...