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TEAR SUBSTITUTES - DETAILS

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´Water binding agent´ in tear substitutes help to form a tear film of better stability

  • Binding agent for water in Tear substitutes are different types of mostly large molecules from different chemical substance classes.

  • Mostly they are polymers, i.e. larger molecules made up of identical small subunits. In the case of water-binding molecules, this increases the volume of the total bound water.

Film maker

In the strict sense, are Film maker actually only those substances which, like the mucous substances (mucins) in the lowest layer of the tear film, are able to bind the water to the surface of the eye. In some cases, however, all water-binding molecules are also referred to as film formers

OVERVIEW of some important ones ´Water binding agent´ / film maker

There are water-binding molecules in different substance classes:

are e.g.

  • high molecular weight sugars / polysaccharides and celluloseDescendants, e.g.

    • Methyl cellulose, hydroxypropyl methyl cellulose (HPMC), methocel

    • Hygromellose (hydroxypropylmethyl cellulose, HPMC)

  • Further high molecular weight sugars

    • Trehalose (Fungal sugar or mycosis) is a disaccharide (double sugar) that occurs in various bacteria, fungi and plants as a natural protective factor against stress caused by drought and frost and is also supposed to have an osmoprotective effect as cell protection against increased tear film osmolarity (hyperosmolarity) in dry eyes.

    • Tamarind seeds Extract is a polysaccharide made from plant seeds - it is relatively thick when dripped on, but becomes thinner on the eye

  • Further high molecular weight sugars

    • Guaraprolose (Hydroxypropyl guar, HP guar) a vegetable polysaccharide related to gum - is relatively thin when dripped on, but turns into a thick gel on the eye

  • PEG (Polyethyleneglycol, Macrogol) is a polyether with different chain lengths, which are indicated with a number (in tear substitutes e.g. PEG 800)

  • Hyaluronic acid (HA, a special polysaccharide - glycosaminoglyan [GAG], from chains of many double sugars, here from the uronic acid D-glucuronic acid and the amino sugar N-acetyl-D-glucosamine) - HA has a very high water-binding capacity and is one of the most important water-binding substances in Body.

  • Carbomer (Polyacrylic acid) is a high molecular weight polymer of acrylic acid with high water binding. The viscosity depends on the chain length. Acrylates are, among other things, distantly related to polymers in contact lens materials. Carbomer is used in tear substitutes as a thickener to increase viscosity and act as a lubricant. It can also be used as a Emulsifier Stabilize oil-in-water emulsions - this is important because modern tear substitutes should contain an oil component. Carbomer is mostly used as a film former because it forms a protective gel layer on surfaces, similar to the mucin of the lower layer of tear film. Carbomer is therefore used in tear substitutes as a mucin substitute.