Microphthalmia and associated abnormalities in inbred black mice.

Although microphthalmia and anophthalmia develop in many animals, they are a consistent and frequent finding in inbred and congenic strains of C57BL mice. Many investigators fail to take account of an incidence that may be as high as 12%, and this may lead to misinterpretation of experimental results. Further confusion may arise from the higher frequency in female mice and from the effects of various environmental and breeding conditions. In anophthalmic and severely microphthalmic mice, there is faulty tear drainage function, which often leads to ocular infections. It should be emphasized that these infections are a function of the ocular malformations arising from the genetic characteristics of C57BL strains and do not represent a failure in proper animal husbandry practices. Histologic studies confirm the consistency and the variability of the ocular findings in these strains. The eye abnormalities may be unilateral or bilateral and, for unexplained reasons, have a strong predilection for the right eye. Microphthalmia may be subtle and clinical anophthalmia may actually represent severe microphthalmia. Accordingly, any conclusions for these inbred strains regarding the eyes should be accompanied by careful microscopic examination of all animals. The most common findings include central corneal opacities, iridocorneal and corneal-lenticular adhesions, abnormal formation of the iris and ciliary body, cataracts, extrusion of lens cortical material with dispersion throughout the eye, failure of vitreous development, and retinal folding. The incidence of all of these findings is increased by exposure to alcohol at critical stages of embryogenesis. Mesodermal dysgenesis of the anterior segment in human eyes mimics the findings seen in inbred C57BL strains of mice, although severe microphthalmia or anophthalmia is less commonly seen. These similar human findings have been associated with a complexity of chromosomal abnormalities and inheritance patterns. Development of the fetal alcohol syndrome in human eyes also provides a phenocopy of the anterior segment abnormalities of mice and of the human familial syndromes. The events, which result in abnormalities in mice and humans, all center around the time in embryogenesis when the optic cup and lens vesicle are developing. In all instances, the lens tends to be smaller than normal and may be displaced in position with relation to the optic cup. This relationship between lens and optic cup is critical in normal development of other ocular structures, including the iris, ciliary body, vitreous, and retina.(ABSTRACT TRUNCATED AT 400 WORDS)