Foam in the external part of the eye.

Foam in the external part of the eye has been measured at the slit-lamp on 274 normal subjects. Foam occurred in 78%, most frequently in the outer canthus, on the skin round this, and in the lateral half of the lid margin. The age group of 30-50 years predominated. The foam-covered areas averaged 1.1 mm2, the largest amount always being found laterally (0.93 mm2). The lateral amount of foam was maximal in the age group of 30-50 years, while the medial maximum was seen in the age group of 60-70 years. The incidence of foam was not correlated to the lipid layer on the precorneal film, expressibility of Meibomian secretion, scales on the lid margin, or greasy hair. A hypothesis has been advanced for the mainly lateral position of the foam: blinking whips up the foam, which possibly has sebum admixed.