Special Senses System

Eye, Sclera - Metaplasia, Osseous

Narrative
Comment:
Osseous metaplasia of the sclera is an incidental aging change that occurs frequently in Fischer 344/N rats, less often in other common rat strains, and seldom if ever in mice. It consists of single to multiple, discrete foci of well-differentiated, mineralized bone. Occasionally, similar scleral foci of cartilage are observed (cartilaginous metaplasia). These innocuous structures do not incite pathologic changes in the sclera or adjacent tissues.
Recommendations:
Scleral osseous metaplasia should be diagnosed only if treatment related, but it does not need a severity grade (i.e., it should be recorded as "present").
References:

National Toxicology Program. 2007. NTP TR-543. Toxicology and Carcinogenesis Studies of α-Methylstyrene (CAS No. 98-83-9) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). NTP, Research Triangle Park, NC.

Abstract: https://ntp.niehs.nih.gov/go/28010

Yoshitomi K, Boorman GA. 1990. Eye and associated glands. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, CA, 239-260.

Abstract: https://www.ncbi.nlm.nih.gov/nlmcatalog/9002563
  • Image of sclera metaplasia, osseous in the eye from a male F344/N rat in a chronic study

    Eye, Sclera - Metaplasia, Osseous in a male F344/N rat from a chronic study. There are two foci of focal osseous metaplasia (arrow) in the sclera.

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<p>Eye, Sclera - Metaplasia, Osseous in a male F344/N rat from a chronic study. There are two foci of focal osseous metaplasia (arrow) in the sclera.</p>

Eye, Sclera - Metaplasia, Osseous in a male F344/N rat from a chronic study. There are two foci of focal osseous metaplasia (arrow) in the sclera.
<p>Eye, Sclera - Metaplasia, Osseous in a male F344/N rat from a chronic study (higher magnification of Figure 1). This higher magnification image shows a discrete focus of well-differentiated, mineralized bone (osseous metaplasia) in greater detail.</p>

Eye, Sclera - Metaplasia, Osseous in a male F344/N rat from a chronic study (higher magnification of Figure 1). This higher magnification image shows a discrete focus of well-differentiated, mineralized bone (osseous metaplasia) in greater detail.

Author

Margarita M. Gruebbel, DVM, PhD, DACVP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC

Reviewers

Ruth E. Hurley, DVM, PHD, DACVP
Senior Veterinary Pathologist
Huntingdon Life Sciences
North Brunswick, NJ

Robert R. Maronpot, DVM, MS, MPH, DACVP, DABT, FIATP
Senior Pathologist
Experimental Pathology Laboratories, Inc.
Research Triangle Park, NC