Meibomian Gland Changes in the Rhino (hr^hr*) Mouse

The rhino mouse, a single gene recessive mutation, is characterized by abnormal epidermal differentiation and maturation leading to the loss of hair at 1 month of age as well as follicular and epidermal hyperkeratoses. We evaluated the lids and corneas of nine rhino mice and their normal litter mates at various ages from 3 months to 1 year. Tissue specimens were studied by light microscopy, scanning and transmission electron microscopy as well as immunoperoxidase using a polyclonal rabbit anti-keratin antibody. At 3 months of age there was a thickening and hyperkeratiniza* tion of the palpebral epidermis which extended into and included the meibomian gland central duct. Whereas in the skin, hyperkeratinization is followed by follicular hyperkeratosis and dermal cyst formation, in the meibomian gland, ductal hyperkeratinization appeared to lead to loss of well developed acini followed by atrophy of the gland at 1 year as confirmed by immunostaining for keratin proteins. Scanning electron microscopy revealed marked plugging of the meibomian gland orifice with keratinized cells or debris in contrast to the patent orifice of the normal lid. Ocular surface changes included the presence of a whitish exudate covering the surface of the eye and increased numbers of preexfoliative cornea! epithelial cells. These findings suggest that the rhino mouse may represents the first naturally occurring disorder of the meibomian gland. Invest Ophthalmol Vis Sci 29:1190-1194, 1988 The rhino mouse is a single gene recessive mutant (rhrh) which is an allelic variant of the familiar smooth-skinned hairless mouse. At birth, mutant mice appear similar to their normal litter mates, however, by 4 weeks after birth, affected mice show an irreversible hair loss, widening of the pilary canals and the formation of utriculi rilled with homy (keratinized) cells similar to human open comedones. In addition to the loss of hair, there is a general sagging and folding of the skin leading to the characteristic "rhinoceros-like" appearance. Although the morphogenesis of the subcutaneous changes in the rhino mouse has been extensively studied, little is known about associated ocular abnormalities. Previously, Yoshida and coworkers reported that rhino mice may develop spontaneous corneal opacities and corneal epithelial surface irregularities a few months after birth. Since this disorder appears to affect epidermal differentiation we have evaluated the ocular surface including the lids and their associated meibomian glands. Materials and Methods. A total of nine rhino mice and their normal litter mates were evaluated at 3 months, 6 months and 1 to 2 years of age. All animals