Gentle Tears Mechanism of Action

Physiology: Human tears are composed of water, electrolytes, small molecules such as carbohydrates and lipids, and a variety of proteins, several of which have an enzymic function. The principal proteins of tears include lysozyme (an enzyme which attacks bacterial cell walls), lactoferrin (a bacteriostatic protein), secretory IgA antibodies, and lipid binding proteins.
The use of artificial tears has obvious limitations. Artificial tears cannot completely substitute complex composition of natural tears. The integrity of the three-layered lipid, aqueous, and mucin structure, vital to the effective functioning of the tear film is not reproduced.
Artificial tears act by adding volume of the tear film, but they can only do this while they remain in contact with the surface of the eye. A simple saline eyedrop will remain in contact with the eye surface for only a few seconds. Therefore to be effective, a viscosity enhancing component is required in the artificial tear formulation.
The reported prevalence of dry eye garnered from different studies varies substantially from 7.8% to as high as 20%.
Risk factors for dry eye include: Advanced age; Female sex; Menopausal hormone therapy; Low omega-3 fatty acid intake.
Other possible risk factors include: low androgen levels; autoimmune diseases and other disorders; medication use; genetic predisposition; alcohol use.
It has been well-documented that women are twice as likely to develop dry eye and that the prevalence increases significantly with age, most especially in postmenopausal women.
Symptoms: The major symptoms associated with dry eye include: blurred vision, ocular discharge, eye discomfort, a burning sensation, increased awareness of the eye, redness, sensitivity to light, and the feeling of grit or sand in the eye.
An accurate diagnosis may be obtained from patient history.
Patients with dry eye will state that the eye discomfort, such as burning or a feeling of grit, gets worse as the day progresses. Symptoms may start slowly and occur episodically over weeks to months, with the eyes becoming acutely sensitive to environmental insults (e.g., low humidity).
Classification: A classification system for dry eye proposed by the National Eye Institute divides dry eye into 2 categories, of which the first is the more common: Deficiency of aqueous tear production (eg, from Sjögren's syndrome, lacrimal gland disease, lacrimal gland duct obstruction, loss of reflex tearing, LASIK surgery).
Increased tear evaporation (eg, from meibomian gland disorder, exposure, contact lenses, blink abnormality).
Both categories lead to an increase in tear film osmolarity. This increased osmolarity leads to an osmotic dehydration of the surface of the eye and to the symptoms associated with dry eye.
Demulcents: Generally, nonprescription artificial tear products provide sufficient relief of the symptoms of dry eye. Artificial tear products contain demulcents that mimic the action of mucin, protectively covering and wetting the cornea. Substituted cellulose ethers (e.g., carboxymethylcellulose) are water-soluble ingredients that are associated with little if any adverse effects and show a longer duration of action than other demulcents.
Other demulcents found in artificial tear formulations include polyvinyl alcohol and water-soluble polyols, such as glycerin and propylene and polyethylene glycol. Dextran 70 has been shown to be an effective demulcent, but it can cause stinging and blurring. Although transient, these adverse effects may influence patient adherence.
Alternative available products are ocular emollients that produce a protective film that covers the ocular surface. They may contain such compounds as lanolin, mineral oil, paraffin, or petrolatum. They have been shown to cause blurred vision and are therefore recommended to be applied at bedtime.
Pharmacology: Mechanism of Action: Hypromellose, short for hydroxypropyl methylcellulose (HPMC), is a semisynthetic, inert, viscoelastic polymer used as an ophthalmic lubricant, as well as an excipient and controlled-delivery component in oral medicaments, found in a variety of commercial products. It is a hydrogel which is endowed with the property of swelling up in water and retaining moisture. It is a carbomer that has the ability to cling to the eye surface that help reduce frequency of application to 4x daily. It also provides a demulcent action.
Hypromellose solutions were patented as a semisynthetic substitute for tear-film. Its molecular structure is predicated upon a base celluloid compound that is highly water soluble.
Post-application, celluloid attributes of good water solubility reportedly aids in visual clarity. When applied, a hypromellose solution acts to swell and absorb water, thereby expanding the thickness of the tear-film. Hypromellose augmentation therefore results in extended lubricant time presence on the cornea, which theoretically results in decreased eye irritation, especially in dry climates, home, or work environments.
On a molecular level, this polymer contains beta-linked D-glucose units that remain metabolically intact for days to weeks. On a manufacturing note, since hypromellose is a vegetarian substitute for gelatin, it is slightly more expensive to produce due to semisynthetic manufacturing processes. Aside from its widespread commercial and retail availability over the counter in a variety of products, Hypromellose 2% solution has been documented to be used during surgery to aid in corneal protection and during orbital surgery.
Dextran 70 produces osmotic effects similar to albumin. It helps retain fluid through an osmotic effect.
Pharmacological Action: The dextran and hydroxypropyl methylcellulose polymers in Gentle Tears mimic the action of conjunctival mucin helping mucin-deficient states and increasing the ocular retention time in aqueous-deficient states through the adsorption action of the polymers attaching to the ocular surface. The adsorption effect is independent of the viscosity thus ensuring a prolonged wetting action with a low viscosity.
Gentle Tears increases corneal wetting (improves lubrication) as judged by a greatly reduced contact angle on the clean corneal surface (18-21°). (Normal saline: 48-52°).
It increases pre-corneal tearfilm stability, evidenced by tearfilm break up studies.
Gentle Tears smoothens the corneal surface of patients with dry eyes and contributes to improved vision.