A patient might complain of dryness of the eyes simply because the conjunctiva is inflamed, but when the tear film really is defective, the patient might complain of soreness and irritation rather than dryness. The diagnosis of a dry eye depends on a careful examination and it is quite erroneous to assume that the tear film is inade quate simply because the patient complains of dryness, or even if the symptoms appear to be improved by artificial tears.
The normal tear film consists of three layers and the integrity of this film is essential for comfort and more importantly for good vision. The anterior, or outermost, layer is formed by the oily secretion of the meibomian glands and the layer next to the cornea is mucinous to allow proper wetting by the watery component of the tears, which lies sandwiched between the two. This three-layered film is constantly maintained by the act of blinking.
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