Meibomian gland dysfunction. II. The role of keratinization in a rabbit model of MGD.

Meibomian gland dysfunction (MGD) was induced in 34 albino rabbits by the twice-daily topical application of 2% epinephrine over a period of 6 months to 1 year. Seven age-matched control rabbits, not receiving epinephrine, were followed up for a similar period. All lids were evaluated pre- and post-treatment by gross clinical examination and by transillumination biomicroscopy and photography. Of the 68 rabbit lids evaluated, 56% developed signs of MGD, which ranged from plugging of the meibomian gland orifice and presence of microcysts (subclinical lesions; 30.9% of the lids) to opacification and enlargement of the glands with increasing severity (clinical lesions; 25.0% of the lids). The remaining lids (44%) remained normal. MGD did not develop in the seven control rabbits. After the development of MGD, lids were evaluated by immunofluorescent microscopy, SDS-PAGE and Western blotting using mouse monoclonal antibodies to keratin proteins. Development and progression of MGD in the rabbit appears to correlate with increasing stratification and keratinization of the meibomian gland duct epithelium. In the early stages of MGD, focal areas of epithelial hyperkeratinization were identified by immunohistochemical staining using AE2 monoclonal antibody, specific for the 56.5 kD and 65-67 kD keratin protein marker for keratinized epidermis. As the severity of MGD progressed there was progressive increase in the AE2 staining of the duct epithelium. SDS-PAGE and immunoblotting of proteins from meibomian gland excreta in chronic MGD showed a progressive increase in both the 56.5 kD and 65-67 kD keratinization protein markers during development of MGD. We conclude that hyperkeratinization of the duct epithelium leading to plugging and dilation of the meibomian gland underlies the development of MGD following topical epinephrine treatment.