Transition® lenses

In his position as Associate Director of Research and Development, Optical Products, Dr. Crano managed the entire photochromies research program. He led the team of scientists that synthesized and evaluated hundreds of candidate photochromic dyestuffs, and directed all of the product and process development involved in the various Transitions lenses. In addition, his responsibilities included R D on non-ophthalmic photochromic applications, and on other optical coatings and resins. 

He has a number of US patents in various areas of technology, including three during 1990-2 that cover the basic compositions and methods for producing the first generation of Transitions lenses. These were important in establishing a strong proprietary position in photochromic plastic ophthalmic lenses. In addition, he had published several reviews and invited lectures on photochromism and photochromic polymers. 

Separation upon conditions This separation strategy entails that the system under Condition 1 exhibits property (-I-P), and under Condition 2 it exhibits property (-P). An excellent example is Transitions lenses with a light-sensitive photochromic coating. The lenses are light or dark depending on the amount of UV radiation present (Exhibit 24.3). 

Figure 2.10. Photochromic performance of a Transitions lens. (Reprinted from Ref. 45 with permission of copyright owner Chapman Hall Ltd.)...

In photoluminescence one measures physical and chemical properties of materials by using photons to induce excited electronic states in the material system and analyzing the optical emission as these states relax. Typically, light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distribution and time dependence of the emission are related to electronic transition probabilities within the sample, and can be used to provide qualitative and, sometimes, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. 

Ascorbate is known to act as a water-soluble antioxidant, reacting rapidly with superoxide, hydroxyl and peroxyl radicals. However, reduced ascorbate can react non-enzymatically with molecular oxygen to produce dehydroascorbate and hydrogen peroxide. Also, ascorbate in the presence of light, hydrogen peroxide and riboflavin, or transition metals (e.g. Fe, Cu " ), can give rise to hydroxyl radicals (Delaye and Tardieu, 1983 Ueno et al., 1987). These phenomena may also be important in oxidative damage to the lens and subsequent cataract formation. 

Peroxides are very toxic to the cornea of the eye. After the disinfection cycle, and before placing the lens in the eye, hydrogen peroxide must be completely neutralized by reducing agents, catalase, or transition metals, such as platinum. 

Fig. 3 Transition energy for S0 — Sj (red) and S0 — CT(black) for a tryptophan during a 2 ns QM-MM trajectory of the human eye lens protein yD-crystallin showing typical fluctuations due to rapid changes in local electrostatic potentials at the atoms of the chromophore. This Trp has a low quantum yield because the CT state is near the Sj state much of the time. Heterogeneity in lifetime and wavelength are evident in both states because regions of 100 ps are seen having distinctly different average energies...

The temporal response of the thermal lensing technique is limited by the acoustic transit time the heated liquid must expand in volume for the lens to be formed and this depends in particular on the size of the heated region. In practice the observation time scale is of about 1 ps to a few ms. 

A simple approach to oxidant control of the Na+/H+ exchanger would be monomer-dimer transition based on SH to S-S transition. This linkage has been observed in isolated membranes without change in activity. On the other hand, the exchanger activity in membrane vesicles from eye lens is activated by H202 which could be based on oxidation of SH groups (Ye and Zadunaisky, 1992). 

Fic. 2. Chemisorption and dissociation of a diatomic AB. (a) The traditional Len-nard-Jones one-dimensional potential diagram E versus R, where R is an ill-defined reaction coordinate, say the AB-surface distance, (b) The conventional two-dimensional potential diagram E versus R(x, y). The reaction coordinates are the A — B distance ( ) and the AB-surface distance (y). The energy minima correspond to the (nondissociated) molecular chemisorbed state DAB + QAB and atomic (dissociated) chemisorbed state gA + gB, the maximum to the transition state (TS) with some finite A — B bond length, (c) The multidimensional BOC potential diagram, similar to (b), but the reaction coordinate is the A — B bond order xAB. The M — AB bond order is conserved to unity (xA + xAB + xB = 1) up to the transition state where 1 > = c > 0 and 8 = 1/2(A ,abj6 + gAB). See text for notations... 

N Strater, WN Lipscomb (1995) Two-metal ion mechanism of bovine lens leucine aminopeptidase active site solvent structure and binding mode of L-leucinal, a gem-diolate transition state analogue, by X-ray crystallography, Biochemistry 34 14792-14800... 

A second generation lens, the Transitions Plus lens, was introduced in November 1992. In the years since, Transitions Optical has marketed a succession of new lenses. In September 1994 the EuroBrown lens appeared, formulated to give when activated a brown color, especially favored in the European market. The mid-index Transitions III lenses were launched in the United States and in Europe during 1996, and the Transitions XTRActive lenses were introduced in the US in January 1997. The most recently introduced lenses are Transitions III lenses in a standard index matrix. These use the latest technology in organic photochromic dyestuffs and polymer science and engineering, and maintain the company s position... 

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