Applications in Ophthalmics

The three main classes that have been much studied for ophthalmic applications are spiroindolinonaphthoxazines (see section 1.2.3), diarylnaphthopyrans (see section 1.2.4) and fulgides (see section 1.2.5). How these different photochromic classes match up to the desired criteria for use in lenses is shown in Table 1.9. From this it can be seen that fulgides exhibit only a fair fatigue resistance and spiroindolinonaphthoxazines suffer from a high temperature dependency. Consequently, for this photochromic outlet, naphthopyrans have become the molecules of choice. Typical 

Class Performance (OD, act/fade rate) Temperature dependency Fatigue 

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Medicinally, cocaine is of value as a local anaesthetic for topical application. It is rapidly absorbed by mucous membranes and paralyses peripheral ends of sensory nerves. This is achieved by blocking ion channels in neural membranes. It was widely used in dentistry, but has been replaced by safer drugs, though it still has applications in ophthalmic and ear, nose, and throat surgery. As a constituent of Brompton s cocktail (cocaine and heroin in sweetened alcohol) it is available to control pain in terminal cancer patients. It increases the overall analgesic effect, and its additional CNS stimulant properties counteract the sedation normally associated with heroin (see page 332). 

J. C. Crano, T. Flood, D. Knowles, A. Kumar, and B. Van Gemert, Photochromic compounds chemistry and application in ophthalmic lenses, Pure Appl. Chem., 68, 1395-1398 (1996). 

All povidone types have applications in ophthalmic solutions [83-86,102, 267, 354]. Povidone K 17, povidone K 25 and povidone K 30 are usually used in eye drops while the higher-molecular type, povidone K 90, is preferred for contact lens solutions [87,88,203,382]. It is usually added to these dosage forms in concentrations between 2% and 10% and performs the functions shown in Table 101. 

Crano, J. C., Flood, T., Knowles, D., Kumar, A., VanGemert, B., Photochromic Compounds Chemistry and Application in Ophthalmic Lenses, Pure Appl. Chem. 1996, 68, 1395 1398. 

The total biomedical PEG literature includes thousands of papers and hundreds of applications. Some of the applications, in addition to those mentioned above, include dmg delivery depots, cell encapsulants, lubricious surfaces, mucoadhesive dmg carriers, coatings for miaofluidic devices, antibacterial coatings, nonthrombogenic coatings, control of cell fusion, applications in ophthalmic implants, and separation membranes. 

Examples of silicones in ophthalmic application have been described.5 1 However, some problems have been reported with the use of silicones in retinal tamponade.542 Silicones are widely used in contact lenses because of their unusually good oxygen permeability and bioinertness, but the need for novel materials continues. Low-modulus fluorosiloxane-based hydrogel lenses with a wide range of water content and high-oxygen permeability have been described in a number of papers.543-... 

The reaction product of dimethyl malonate and 1,6-hexanediol with dimethyl-aminobenzaldehyde, 4-methoxy-benzaldehyde, and 3-nitrobenzaldehyde was previously prepared by the authors (2) and used in ophthalmic applications. 

Nadolol is noteworthy for its very long duration of action its spectrum of action is similar to that of timolol. Timolol is a nonselective agent with no local anesthetic activity. It has excellent ocular hypotensive effects when administered topically in the eye. Levobunolol (nonselective) and betaxolol (E -selective) are also used for topical ophthalmic application in glaucoma the latter drug may be less likely to induce bronchoconstriction than nonselective antagonists. Carteolol is a nonselective 13-receptor antagonist. 

Not surprisingly, petrolatum has been cited as a major ingredient in patents that describe products for topical skin treatment.93-95 Some specific applications include ophthalmic ointments,96 lip care products,97 98 and aftershave preparations.99... 

Other ophthalmic emulsions have been used to formulate prednisolone, piroxicam and amphotericin B emulsion. Although emulsions can produce sustained therapeutic effects and reduced irritancy of drag, their application in ophthalmology have been limited due to problems of stability. 

For ophthalmic disorders or for topical application in the treatment of various skin disorders, either dexamethasone or its esters may be used. 

Selection of an appropriate base for an ointment or cream formulation depends on the type of activity desired (e.g., topical or percutaneous absorption), compatibility with other components, physicochemical and microbial stability of the product, ease of manufacture, pourability and spreadability of the formulation, duration of contact, chances of hypersensitivity reactions, and ease of washing from the site of application. In addition, bases that are used in ophthalmic preparations should be nonirritating and should soften at body temperatures. White petrolatum and liquid petrolatum are generally used in ophthalmic preparations. Table 1 summarizes... 

Although most commonly used topical anesthetics are similar in onset, duration, and depth of anesthesia (see Chapter 6), several important differences exist. For diagnostic and treatment procedures requiring topical anesthesia, the clinician essentially has two choices tetracaine or proparacaine. Both provide rapid onset of anesthesia within 10 to 20 seconds and last approximately 10 to 20 minutes. If prolonged anesthesia is required, it may be accomplished by repeated application.Tetracaine may cause more discomfort upon instillation than proparacaine and typically results in more corneal compromise. In general, proparacaine 0.5% has a low incidence of hypersensitivity reactions and is the anesthetic of choice for topical anesthesia in ophthalmic applications. Other anesthetics that have occasional topical application are cocaine (4% to 10%) and lidocaine (4%). 

A nanoparticle is a microscopic particle with a diameter less than 100 nm. Nanoparticles were first developed around 1970, and initially they were devised as carriers for vaccines and anticancer drugs. Nanoparticle research is currently an area of intense scientific research because of a wide variety of potential applications in biomedical, optical, and electronic fields. To enhance tumor uptake, the strategy of drug targeting was employed, and as a first important step, research focused on the development of methods to reduce the uptake of the nanoparticles by the RES cells. Simultaneously, the use of nanoparticles for ophthalmic and oral delivery was investigated (17, 18). Recent advancement of nanoparticles and nanosuspensions was caused by their application for pulmonary drug delivery (19, 20). 

Ointments, ophthalmic. Sterile ointments designed for application to the eyelids. Petrolatum, petrolatum-mineral oil, and petrolatum-anhydrous lanolin bases are often used in ophthalmic ointments because of their low irritating potential. Finely powdered, sterile active ingredients are aseptically incorporated into a sterile base, using sterile utensils, and dispensed in sterile ophthalmic-tipped tubes to reduce the possibility of contamination. ... 

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