Tears normal volume

The anterior surface of the eye is constantly rinsed by tear fluid secreted at a flow rate of about 1 pL/min by the main lachrymal gland of the lachrymal apparatus. Tears eventually drain into the nasal cavity through the nasolachrymal ducts. Tear fluid contains mucin, lysozyme, lactoferrin, prealbumin, and serum proteins. It functions as an antibacterial lubricant and aids in draining out foreign substances. The normal volume of tear fluid is 5 to 10 xL.66... 

The normal volume of the tear layer is 8 to 10 mcl, including the fluid trapped in the folds of the conjunctiva. A total volume of perhaps 30 mcl can be held for a brief time if the eyelids are not squeezed after dosing. When a single drop of medication of 50 mcl (0.05 ml) is applied, the nasolacrimal duct rapidly drains the excess, although some may be blinked out of the eye onto the lid. 

The maximum volume of solution the lower conjunctival sac can accommodate is about 30 microlitres. After instillation the normal volume of the precorneal tear film (7-10 microlitres) is established again due to drainage of the extra volume of fluid present. The drainage rate is directly proportional to the volume of ophthalmic solution instilled. A high percentage of hydrophilic active substances are eliminated and lost to the eye. The drained active substance reaches, via the nasolachrymal duct, the nasal mucosae and after absorption enters the systemic circulation. As lipophilic substances are absorbed much more rapidly, these systemic effects are less prominent. 

Draw and label the axes as shown. Note that the x axis is usually drawn without any numerical markers. Normal intracranial volume is assumed to be at the left side of the curve and should be in keeping with an ICP of 5-10 mmHg. Draw a curve similar in shape to a positive tear-away exponential. Demonstrate on your curve that compensation for a rise in the volume of one intracranial component maintains the ICP < 20 mmHg. However, when these limited compensatory mechanisms are exhausted, ICP rises rapidly, causing focal ischaemia (ICP 20-45 mmHg) followed by global ischaemia (ICP > 45 mmHg). 

The nature of competition in multi-protein systems is a question of great interest which is touched on by a considerable number of the papers in this volume. Such interest is understandable in that many of the areas of application involve adsorption from complex media for example blood, plasma or serum, tear fluid and other body fluids, soil, milk, and food products generally. The information normally sought concerns the concentration profile of the proteins on the surface and how this is related to the concentration "profile" in the bulk phase. In general there is a redistribution of proteins in the surface phase, resulting in an enrichment of some components and an impoverishment of others relative to the bulk phase. The redistribution may also be time dependent and the kinetics as well as the equilibrium aspects are of interest. 

The exposed part of the eye is covered by a thin fluid layer, the so-called precorneal tear film. The film thickness is reported to be about 3-10 pm depending on the measuranent method used. The resident volume amounts to about 10 pL. According to the three layers theory, the precorneal tear film consists of a superficial Upid layer, a central aqueous layer, and an inner mncus layer. The lipids play an important role in reducing the evaporation rate in a way that normal tear osmolality can be maintained, even when the tear flow is quite low. - ... 

Under normal baseline, the total volume required to cover the eye surface is approximately 6-8 p L, the tear secretion rate is about 1.2 pL/min and the rate of lacrimal turnover per minute is 16 % of total tear volume. However in stimulus conditions, by irritation of the conjunctiva or cornea reflects, tearing occurs. The volume of the tear film grows to about 16 ml, with a range between 5 and 6 pL [7]. Thus reflex tearing stimulated for any reason, including many parameters of eye drop formulation to enhance solubility and stability of the dosage form, cause an accelerated drop instilled washing. 

---