- Keratoconjunctivitis sicca (KCS) results from a deficiency of the precorneal tear film in which either an inadequate quantity or deficient quality of tears are produced.
- The precorneal tear film is composed of 3 layers:
- Inner mucin layer: adheres the tear film to the cornea
- Middle aqueous layer: provides corneal nutrition and waste removal
- Outer lipid layer: prevents evaporation of the tear film
- Quantitative deficiency involves the aqueous layer, which is produced by the orbital and nictitating membrane (NM) lacrimal glands.
- Qualitative deficiency involves the mucin layer, which is produced by conjunctival goblet cells, or the lipid layer, which is produced by meibomian glands.
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