Dry Eye Disease (Keratoconjunctivitis Sicca)
Description of the Disease and Clinical Presentation
The tear film consists of its watery component, secreted by the lacrimal glands, and then the lipid and mucoid components, secreted by the glands of the eyelid margin and goblet cells of the conjunctiva. Dry eye disease represents a progressive inflammatory condition of the cornea and conjunctiva caused by a lack of tears, either qualitatively—due to a lack of lipid and mucoid components—or quantitatively, due to reduced secretion by the lacrimal glands. The reasons for the occurrence of dry eye disease are numerous, and the disease most frequently occurs as a result of autoimmune and allergic conditions, certain infectious diseases (distemper), endocrine diseases (hypothyroidism, Cushing's syndrome, diabetes), pancreas inflammation, neurological disorders affecting peripheral nerves, due to the action of toxic substances and certain medications (sulfa drugs), as well as after removal of the third eyelid gland. The affected animal develops conjunctivitis, with pronounced hyperemia and swelling of the conjunctiva, and keratitis (inflammation of the cornea), which is often pigmented and/or ulcerated. Vascularization of the cornea is present, and scars on the cornea can significantly affect the quality of vision. Without adequate tear presence, the eye is susceptible to bacterial infections, and therefore a discharge of a mucopurulent nature can often be observed. The animal experiences discomfort or pain, and blepharospasm is present. The changes are most often present in both eyes but are of varying intensity. Dogs are more commonly affected, and in cats, if dry eye disease occurs, the clinical picture is less pronounced. There are breeds of dogs prone to this disease, and dry eye disease is more commonly diagnosed in middle-aged or older dogs.
 
Therapy
The amount of tears is measured by the Schirmer test, and the quality of the tear film can be determined by the tear film breakup test, imaging of Meibomian glands (Meibomioscopy), and molecular evaluation of the tear composition. Therapy involves the local application of lacrimostimulants (topical cyclosporine, tacrolimus) and artificial tears. The primary cause of disease should be eliminated or controlled  - good control of the immune-mediated disease resulting in the damage of lacrimal glands, good control of allergies, and good control of pancreas inflammation or other endocrine and neurological diseases is extremely important for therapeutic success. This condition is in general not curable, but it is treatable, and life-long medical treatment is usually needed. If satisfactory results are not achieved with medical therapy, transposition of the parotid duct is performed, whereby the salivary duct from the mouth is surgically moved to the lower eyelid, thereby allowing saliva to lubricate the eye surface.
 
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