The Eye

The eye is not, of course, a general route for the administration of drugs to the body, although it has been explored for the systemic delivery of peptides and proteins such as insulin. It is considered here because absorption of drugs does occur from medication applied to the eye, producing sometimes toxic systemic effects, although often the desired local effect is on the eye or its component 

Dmgs are usually applied to the eye in the form of drops or ointments for local action. The absorbing surface is the cornea. Dmg absorbed by the conjuctiva enters the systemic circulation. It is useful to consider some of the properties of the absorbing surfaces and their environment. 

The eye (Fig. 9.32) has two barrier systems a blood-aqueous barrier and a blood-vitreous barrier. The former is composed of the ciliary epithelium, the epithelium of the posterior surface of the iris, and blood vessels within the iris. Solutes and drugs enter the aqueous humour at the ciliary epithelium and at blood vessels. Many substances are transported out of the vitreous humour at the retinal surface. Solutes also leave the vitreous humour by diffusing to the aqueous humour of the posterior chamber. 

Tears comprise inorganic electrolytes - sodium, potassium and some calcium ions, chloride and hydrogencarbonate counterions - as well as glucose. The macromolecular components include some albumin, globulins and lysozyme. Lipids which form a monolayer over the tear 

Modified from J. R. Robinson (ed.), Ophthalmic Drug Delivery Systems, American Pharmaceutical Association, Washington DC, 1980. 

It is commonly stated that there are 15 specific causes of colour, arising from various physical and chemical mechanisms. These mechanisms may be collected into five broad groupings  

This book is focussed on the industrially important organic dyes and pigments and, to a certain extent, inorganic pigments and thus deals mostly with colour generated by the mechanisms described by group (c), although the reader will find examples of the other mechanisms on occasions also. 

A useful measure of the strength or intensity of the colour of a dye is given by the molar extinction coefficient (s) at its value. This quantity may be obtained from the UV/visible absorption spectrum of the dye using the Beer-Lambert Law, i.e.  

Visible reflectance spectroscopy is used routinely to measure the colour of opaque objects such as textile fabrics, paint films and plastics for purposes such as colour matching and dye and pigment recipe prediction. There is now a wide range of commercially-available reflectance spectrophotometers used industrially as colour measurement devices for such purposes. In many ways, this technique may be considered as complementary to the use of visible absorption spectroscopy for the measurement of transparent dye solutions. Reflectance spectra of typical red, green and blue surfaces 

Mathematical approaches that make use of concepts associated with colour space for colour measurement and specification based on reflectance spectroscopy have become well-established. Indeed the calculations involved are normally implemented in the software that is provided within an instrument used for colour measurement. The basis of all colour measurement systems is the CIE system of colour specification, which was agreed in 1931. The Commission Internationale de I Eclairage (CIE) is an international organisation promoting cooperation and information exchange on matters relating to the science and art of lighting. An important approach used for the 

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M.p. 114-116 C. Prepared by racemization of hyoscyamine. It and its salts are used to dilate the pupil of the eye. Given internally they reduce the secretion of saliva and relieve spasmodic pains. 

Cortisone is a hormone produced by the cortex of the adrenal glands. As with other adrenal corticoid steroids, administration of cortisone leads to an increased deposition of liver glycogen. Tt can remove features of rheumatoid arthritis, but does not check the underlying disease it is used in various diseases of the eye, and is an antiallergic and anlifibroplastic agent. 

Contrast C is the contrast of the luminances between the object Lo and its surroundings Ls C = (Lo - Ls)/Ls. With increasing contrast, visibility increases Adaptation luminance L,d, is the luminance to which the eye adapts its sensitivity. It corresponds to the luminance of the field of vision. With increasing adaptation luminance, visibility increases. 

Object dimension is defined as the viewing angle in radiant minutes under which the eye observes tbe object. With increasing dimension, the visibility increases. 

We confine ourselves here to scanning probe microscopies (see Section VIII-2B) scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in which successive profiles of a surface (see Fig. VIII-1) are combined to provide a contour map of a surface. It is conventional to display a map in terms of dark to light areas, in order of increasing height above the surface ordinary contour maps would be confusing to the eye. 

Light microscopy is of great importance for basic research, analysis in materials science and for the practical control of fabrication steps. Wlien used conventionally it serves to reveal structures of objects which are otherwise mvisible to the eye or magnifying glass, such as micrometre-sized structures of microelectronic devices on silicon wafers. The lateral resolution of the teclmique is detennined by the wavelength of tire light... 

The real image is seen by the eye as a virtual image at 25 cm distance, the nomial distance for distinct vision. 

The intensity of the reflected light must also be measured. Historically, this was done using the eye. Since, in general, a null (a measurement of the point at which the light decreases to zero) is required, this can be relatively sensitive. However, nowadays, the light intensity is generally measured using a photomultiplier tube. 

Almost everyone has a concept of pressure from weather reports of tlie pressure of the atmosphere around us. In this context, high pressure is a sign of good weather while very low pressures occur at the eyes of cyclones and hurricanes. In elementary discussions of mechanics, hydrostatics of fluids and the gas laws, most scientists leam to compute pressures in static systems as force per unit area, often treated as a scalar quantity. They also leam that unbalanced pressures cause fluids to flow. Winds are the flow of the atmosphere from regions of high to low... 

Figure B2.5.19. The collisional deactivation rate constant /c, (O3) (equation B2.5.42 ) as a fimction of the vibrational level v". Adapted from [ ]. Experimental data are represented by full circles with error bars. The broken curve is to serve as a guide to the eye.

Figure B3.2.7. A perspective view of the cetineite (Na Se). The height of the figure is tluee lattice constants c. The shaded tube is included only as a guide to the eye. (From [88].)...

Soreness which may follow ver minor accidents to the eye may he relieved bv placing i drop of castor oil in the corner of the eye. 

Safety goggles should always be worn over the eyes when carrying out potentially dangerous operations, e,g. vacuum distillations, distillation of large volumes of inflammable liquids and experiments employing large quantities of metallic sodium. 

Protection of the eyes. Safety goggles should always be... 

Method 2. Mix 1 0 g. of 3 5-dinitrobenzoic acid with 1 5 g. of phosphorus pentachloride in a small, dry test-tube. Warm the mixture gently over a small smoky fiame to start the reaction when the reaction has subsided (but not before), boil for 1-2 minutes or until the solid matter has dissolved. Pour the mixture while still liquid on a dry watch glass (CAUTION the fumes are irritating to the eyes). When the product has solidified, remove the liquid by-product (phosphorus oxychloride) by transferring the pasty mixture to a pad of several thicknesses of filter paper or to a small piece of porous tile. Spread the material until the liquid has been absorbed and the residual solid is dry. Transfer the 3 5 dinitrobenzoyl chloride to a test-tube, add 0-5-1 ml. of the alcohol, and continue as in Method 1. 

Ethyl bromoacetate vapour is extremely irritating to the eyes. The preparation must therefore be conducted in a fume cupboard provided with a good draught the material should be kept in closed vessels as far as possible. 

Impure quinone may be purified by placing it in a distilling flask attached to a condenser and passing a rapid current of steam into the flask the quinone Sublimes and collects in the receiver. It is separated from the water by filtration and dried the m.p. is 116°. The vapour has a penetrating odour and attacks the eyes. 

Acid in the eye. If the acid is dilute, wash the eye repeatedly with 1 per cent, sodium bicarbonate solution in the eye cup. If the acid is concentrated, first wash the eye with a large amount of water and then continue with the bicarbonate solution. 

Caustic alkali in the eye. Proceed as for acid in the eye, but wash with 1 per cent, boric acid solution in place of bicarbonate solution. 

Bromine in the eye. Wash thoroughly with water and then immediately with 1 per cent, sodium bicarbonate solution. 

Glass in the eye. Remove loose glass very gerUly with forceps or by washing with water in an eye bath. Call for a doctor immediately. 

Care should be taken in handling and using iodine, as contact with the skin can cause lesions iodine vapor is intensely irritating to the eyes and mucus membranes. The maximum allowable concentration of iodine in air should not exceed 1 mg/nu (8-hour time-weighted average -40-hour). 

There is often a fundamental disparity between the graphic ability of computer monitors and that of printers. Monitors may use anywhere from 8-bit color (256 colors) to 24-bit color (16 million colors). Printers, except for dye sublimation models, use four colors, which are printed in a pattern that tricks the eye into seeing all colors. Monitors generally use about a 72-dpi (dots per inch) screen resolution, as compared to printer resolutions of 300 dpi or better. 

In biological systems molecular assemblies connected by non-covalent interactions are as common as biopolymers. Examples arc protein and DNA helices, enzyme-substrate and multienzyme complexes, bilayer lipid membranes (BLMs), and aggregates of biopolymers forming various aqueous gels, e.g, the eye lens. About 50% of the organic substances in humans are accounted for by the membrane structures of cells, which constitute the medium for the vast majority of biochemical reactions. Evidently organic synthesis should also develop tools to mimic the Structure and propertiesof biopolymer, biomembrane, and gel structures in aqueous media. 

Crane scales are designed to be inserted between the hook of a crane and the load being lifted. The upper end of the scale has an eye which attaches to the crane s hook, whereas the lower end has a hook that picks up the load. A tension-type load cell connects the eye and hook. The display may be either integral with the load cell or remotely mounted. Capacities range up to 50 t. 

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