A Clinical Case from the Archives : 17/09/2004

What are the white lesions at the limbus in this 5 year old guinea pig? What is the likely pathogenesis that underlies them and are they a problem to the animal?

These are so-called heterotopic bone formation, well recognised at this site in guinea pigs. The likely pathogenesis centres around the movement of vitamin C into the aqueous at the ciliary body. Excessive ascorbic acid at this site can lead to new bone formation at the limbus in the same way in which it is important in bone deposition more generally (Kipp et al: Long-term low ascorbic acid intake reduces bone mass in guinea pigs. J Nutr. 1996 126:2044-9). These lesions are probably of little consequence to the animal, and while they might interfere with aqueous drainage, glaucoma is not a common consequence of heterotopic bone formation here. The condition used to be termed oseous choristoma, hence two useful case reports are Brooks et al Heterotopic bone formation in the ciliary body of an aged guinea pig. Lab Anim Sci. 1990 40:88-90 and Griffith et al Osseous choristoma of the ciliary body in guinea pigs. Vet Pathol. 1988 25:100-2.


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