Measurement of wettability of the corneal epithelium

Abstract

Adult rabbit corneas were saline-rinsed, mucolytic-rinsed, or wiped to remove mucus. The corneas were alllowed to dry in air; sessile droplets of saline were placed on the surface at various drying time, and their equilibrium contact angle .theta. measured. Several stages of drying can be distinguished: 1) an initial period when excess water is present, with either complete spreading of droplets or very low value of .theta.; 2) a ''plateau'' region lasting about 20-25 min in which .theta. is low and changes slowly with time, and reflects the intrinsic wettability of the surface; 3) a region when more severe drying takes place and .theta. rises sharply. Computed tables are used with known values of .theta. and the surface tension of the saline drops, to give the surface tension of the corneal surface and the interfacial tension between cornea and saline. Acetycysteine-washed corneas showed a plateau value of about 16.degree. and corneal surface tension of 69.3 mN/m. Rinsed corneas remainly fully wettable (.theta. = 0.degree.) for longer than 90 min; hence the plateau value must also be near zero and corneal surface tension about 72 mN/m. Mechanically-wiped corneas dried more rapidly and .theta. rose continuously with no marked plateau value, indicating much lower wettability due to cellular damage (about 40 mN/m).