Lacrimal fluid

May discolor skin from pink fo brownish-black, as well as discoloring the conjunc-tivae, lacrimal fluid, sweat, sputum, urine, and feces skin discoloration may take several months or years to disappear after discontinuation of therapy... 

TAC of lacrimal fluid decreased with the progress of primary open-angle glaucoma. Blood plasma TAC decreased significantly in the third far-advanced stage. A course of total antioxidant vitamin therapy normalized plasma TAC even in patients with far-advanced glaucoma, whereas the lacrimal TAC did not normalize (M4). 

M4. Makashova, N. V., Babenkova, I. V., and Teselkin, I. O., The antioxidant activity of the lacrimal fluid in patients with primary open-angle glaucoma. Vestn. Oftalmol. 115,3-4 (1999). 

Proteins dissolved in the lacrimal fluid influence the viscosity of human tears, which ranges from 1.3 to 5.9 cps with a mean value of 2.92 cps. The tears have a pseudoplastic character with a yield value of about 32 cps at 33 °C. During a blink the lid moves at a high velocity and the film is submitted to a high rate of shear of about 10,000-40,000... 

The surface tension of tear fluid at the eye temperature has been measured as 43.6 to 46.6 rriNm-1 for normal eyes and 49.6 mNm"1 for patients with dry eye. The instillation of a solution containing drugs or adjuvants that lower the surface tension may dismpt the outmost lipid of the tear film into numerous oily droplets, which become solubilized. The protective effect of the oily film against evaporation of the tear film aqueous layer disappears and diy spots will be formed. The dry spots are painful and irritant and elicit reflex blinks to eliminate the material. This irritation does not always occur immediately after the instillation. In many cases it appears 30 minutes to 1 hour following the application and is dependent on the substance and on its concentration. The tear film is destabilized when the surface tension of the instilled solution is much lower than the surface tension of the lacrimal fluid. 

In the case of ionized compounds (weak acids and bases), drug permeation depends on the chemical equilibrium between the ionized and the un-ionized form, both in the delivery system itself and in the lacrimal fluid. In general, un-ionized molecules penetrate lipid membranes more readily than ionized ones. 

Osmotic Pressure The osmolality of the lacrimal fluid is mainly dependent on the number of ions dissolved in the aqueous layer of the tear film and normally ranges between 310 and 350mOsm/kg [44], When an ophthalmic solution is instilled into the eye, it mixes with the tear fluid, resulting in an osmotic pressure that is dependent on the osmolality of the tears as well as that of the formulation and the amount of the formulation instilled. In general, hypotonic solutions are better tolerated by... 

The tears are an example of a compartment with constant turnover, because the inflow of lacrimal fluid is constant and equal to the outflow through the puncta. Consider the fete of sodium fluorescein, a diagnostic tracer representative of a highly hydrophilic drug Once instilled it mixes rapidly with the tears, and the tear flow carries away a portion per unit time, dependent on the drug concentration present. 

Two major types of advanced drug release systems have been designed on the basis of insertion of a solid device in the eye.The first is a device of low permeability filled with drug (Ocusert), which has been discontinued. The second is a polymer that is completely soluble in lacrimal fluid, formulated with drug in its matrix (Lacrisert). Both systems can be made to approach zero-order kinetics. However, patient acceptance has been poor. 

The action of the blink also fecilitates tear drainage (see Figure 24-1). The eyelids direct the lacrimal fluid along a channel formed by the globe and the plica semilunaris toward the inner canthi for drainage into the puncta. 

Because the eyelids represent the distribution system for lacrimal fluids, their neural, muscular, and structural... 

Body secretions HCV antibodies and HCV RNA could be detected in saliva, sweat, urine, ascites, ejaculate, breast milk, bile and lacrimal fluid. It can be assumed that (as with hepatitis B) the occurrence of HCV in various body fluids is directly correlated to the HCV concentration in the serum. (268, 290, 330, 338, 343)... 

A recent approach to ocular inserts was presented by Chetoni et in a study of cylindrical devices for oxytetracycline, made from mixtures of silicone elastomer and grafted on the surface of the inserts with an interpenetrating mueoadhesive polymeric network of polyacrylic acid or polymethacrylic acid. The inserts were tested for drug release and retention at rabbit eyes. It was shown that some of the inserts are able to maintain prolonged oxytetracycline concentrations in the lacrimal fluid for 36 h. 

Unlii N, Ludwig A, van Ooteghem M, et al. Formulation of carbopol 940 ophthalmic vehicles, and in vitro evaluation of the influence of simulated lacrimal fluid on their physico-chemical properties. Pharmazie 1991 46 784-788. 

Marcozzi G, Liberati V, Madia F, Centofanti M, de Feo G. Age- and gender-related differences in human lacrimal fluid peroxidase activity. Ophthalmologica 217(4) 294-297, 2003. 

The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing two-thirds of the eye s focusing power. Because there are no blood vessels in the cornea, it is normally clear and has a shiny surface. The adult cornea has a radius of approximately 7-8 mm that covers about one-sixth of the total surface area of the eye ball that is a vascular tissue to which provides nutrient and oxygen supplied via lacrimal fluid and aqueous humor as well as from blood vessels of the junction between the cornea and sclera. 

Conventional soft contact lenses (SCLs) have the ability to absorb a number of drugs. They can be loaded when the lenses are pre-soaked in the drug solution, - subsequently releasing them into the post-lens lacrimal fluid. As an alternative, one can also insert conventional SCLs into the eyes... 

The hydrogels were able to prevent drug leakage to a common conservation liquid for SCLs and to sustain drug delivery in lacrimal fluid for 2 weeks. The hydrogels with pendant pCDs are particularly useful for the development of cytocompatible medicated implants or biomedical devices, such as drug-loaded SCLs. 

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