Analysis of the free fatty acid component of meibomian secretions in chronic blepharitis.

Meibomian secretions were collected from 43 patients with chronic blepharitis and 8 normal controls. Patients were divided into six clinically distinct groups of chronic blepharitis. Individual secretions were weighed and separated into specific lipid classes by thin-layer chromatography. The free fatty acid (FFA) fraction was recovered, methylated, and analyzed by gas-liquid chromatography. Quantitation was achieved through the use of an internal standard, and qualitative analyses were aided by the use of commercial external standards. Carbon numbers were expressed in terms of their equivalent chain lengths (E.C.L.). For statistical comparisons, specific acid weights were expressed as nanograms per milligram of secretion. Data from individual subjects were tabulated by group and analyzed by a nonparametric analysis of variance. The FFA portion made up from 0.21% to 1.3% of the total meibomian secretion. Acids ranged in length from 12 to 29 carbon atoms. Iso-branched and anteisobranched carbon chains made up approximately 33% of the FFA fraction. E.C.L.'s corresponding to C16:0, C18:0, and C18:1 together made up a major portion of the total FFA fraction (mean = 49%). When compared to normals, a significantly decreased amount of C12:0 was seen in the mixed seborrheic/staphylococcal group and the meibomian seborrhea group. A significantly decreased amount of anteiso-branched C15:0 was seen in the mixed seborrheic/staphylococcal group. Significantly decreased amounts of anteiso-branched C23:0 were seen in all of the seborrheic blepharitides. A significantly increased amount of isobranched C22:0 was seen in the meibomian keratoconjunctivitis group. No significant differences were seen in the staphylococcal group.