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Osseous metaplasia in ciliary body of guinea pig - case report

Osseous metaplasia has been reported within ocular lesions in humans and some animals. Clinically, it is presented as a white irregular mass with variable vascularisation that extends throughout the root of the iris into the anterior part of the anterior chamber. In guinea pigs, this formation is often called heterotopic bone formation or osseous choristoma. Histologically, it consists of bony spicules surrounded by a fibrous envelope, sometimes with haematopoietically active marrow. Guinea pigs are susceptible to ectopic mineralisation due to dietary factors. Affected animals tend to be older, with 15% of them having mineralisation elsewhere. A male guinea pig, 4 years old, was presented for an ophthalmologic examination due to enlargement of the right eye and blink inability that lasted for three days. White irregular plaques were noted in the iridocorneal angle that extended onto the anterior surface of both irides. The findings were significantly more present in the right eye, with the involvement of the iridocorneal angle throughout the whole circle. Intraocular pressures were measured by applanation tonometry valued 27 mmHg for the right eye and 17 mmHg for the left eye (normal limits range from 13 to 21 mmHg). Fluorescein stain did not reveal any corneal lesions. A radiopaque ring of mineral origin was noted on radiography in both irides. The guinea pig was treated with carbonic anhydrase inhibitors (dorzolamide 2% with timolol 0.5%) two times daily for the right eye. After two weeks of therapy, the blink reflex returned to normal, and the intraocular pressure in the right eye decreased to the normal range and valued 21 mmHg. Osseous metaplasia of the ciliary body can be a common finding in older guinea pigs and usually has no clinical significance. This case presents a complication of osseous metaplasia by narrowing the iridocorneal angle, causing secondary glaucoma, which can be successfully treated with carbonic anhydrase inhibitors.

Osseous metaplasia, ciliary body, glaucoma, guinea pig

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