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Tear Film Stabilization

Clinician's Brief (Capsule)

Ophthalmology

|May 2015

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The tear film consists of several layers: a mucin layer covering the ocular surface; an aqueous layer above that; and a lipid layer that covers the tear film surface. Mucin is important because it helps create a smooth refractive surface, decreases shear force between the corneal epithelium and aqueous layer, inhibits microbe adhesion, and prevents drying. Diquafosol is a P2Y2 purinergic receptor agonist that stimulates aqueous tear and mucin secretion from conjunctival epithelial and goblet cells respectively. In this study, Western blotting and immunohistochemical analysis demonstrated that P2Y2 receptors were present in canine conjunctivae at the level of the conjunctival epithelium and goblet cell surfaces. Following administration of 3% diquafosol to 6 laboratory dogs, there was an increase in goblet cell mucin secretion; however, this required at least 180 minutes. Diquafosol may have some use in dogs to treat corneal epithelial disorders.

Commentary

Poorly responsive cases of canine keratoconjunctivitis sicca represent a frustrating subset of patients presenting to the veterinary practitioner. This creates a niche market for the development of novel topical products to improve and stabilize the tear film. The results of the pilot study, which used normal dogs in an experimental setting, may support the ongoing investigation of the use of 3% diquafosol ophthalmic solution in dogs diagnosed with clinical tear film abnormalities or corneal epithelium disorders. Few new products of this type are re-evaluated in the form of peer-reviewed, masked, prospective clinical studies; this charges the general practitioner with making an anecdotal judgment call of cost vs benefit. The reality is that many of the pharmaceutical tear-stabilizing compounds available fail to result in a significant impact when prescribed to dogs with clinical disease when subjectively compared to products labeled for ocular lubrication alone. The cost of any new product thus must be carefully weighed against the true expectation for improvement in patient comfort and clinical signs.—Allyson Gosling, DVM

References

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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