DESICCATION OF THE PRECORNEAL FILM

The cornea is covered by a thin liquid film called the precorneal film. This film plays an important part in the nutrition, lubrication and coating of the cornea. N . Ehlers regards the precorneal film as a layer of fluid enclosed in a thin lipoid layer separating the former superficially from the air and on the inside from the corneal epithelium (Ehlers 1965 A). The precorneal film is kept distended between the palpebral borders, which act as a frame for the film. The film thus covers not only the exposed part of the cornea, but also the exposed part of the bulbar conjunctiva. I t would therefore be most correct to call it the pre-ocular film. The remaining part of the conjunctival sac, the retropalpebral space, is covered by an epithelium whose surface is marked by mucus, and not by lipoid. The precorneal film is the thickest immediately after blinking. Ehlers, in five subjects, noticed an average thickness of 8.7 p 0-2 seconds after blinking. The thickness was gradually reduced to on an average 4.5 ,p 30 seconds after blinking. The reduction took place at the fastest rate in the beginning. If the subject is called upon to avoid blinking, a hole will gradually occur in the precorneal film. This phenomenon has been observed in both normal and pathological cases.