[Principles of intraocular ossification exemplified by secondary choroid ossification]

Intraocular ossification seems to follow general pathogenic principles. Ossification requires besides local changes in carbon dioxide tension and local increase of phosphate ions first a rich vascular supply--therefore the peripapillary region is always involved, alone or in conjunction with other sites--and second probably a direct or indirect influence of the Retinal Pigment Epithelium (RPE). The growth of the bone occurs slowly and leads to a relative uniform morphology. Osteogenesis is triggered by chronic intraocular changes (of the RPE), and ossification is almost always combined with a longstanding retinal detachment. The primary lesion (e.g. trauma, inflammation or tumor) plays a minor or no role. Differences between secondary intraocular bone formation (following a well known lesion) and primary choroidal osteomas could be explained by a different strength of the osteogenic (RPE-)stimulus. In the light of our investigations (29 phthitic or chronically hypotonic eyes, 12 of them with intraocular bone formation) and the literature primary osteomas of the choroid have to be interpreted more likely as secondary processes, possibly following a (birth-)trauma, than as congenital choristomas.