An Ultrastructural Study of DNA Precipitation in the Anterior Segment of Eyes with Retinoblastoma

Abstract The anterior segment of six infant eyes enucleated for retinoblastoma were studied by light and electron microscopy in an attempt to describe the pattern of DNA precipitation. In only one of these cases was extracellular deposition of DNA in the iris and aqueous outflow pathways detectable by routine light microscopy and Feulgen staining. In two cases, ultrastructural examination was necessary to resolve the presence of small discrete electrondense DNA granules (60–200 nm). In three cases, the DNA deposits were found on the anterior surface of the iris, in the mid-iris stroma around blood vessels, and in the outer layers of the trabecular meshwork around Schlemm's canal. Although the quantity of the material varied in the three cases, the similar pattern of distribution appeared to reflect routes of fluid movement within the eye and sites of permeability barriers at which the passage of larger particulate matter is obstructed. The DNA deposits had an affinity for collagen and basal lamina, especially in the iris. Interestingly, they were not phagocytosed by the trabecular endothelial cells. No DNA could be detected ultrastructurally in the anterior segment of the three remaining eyes also enucleated for retinoblastoma. The authors' findings suggest that DNA deposition in the anterior segment may be a more common phenomenon in retinoblastoma than has been suspected previously from routine histopathologic studies. The findings are discussed in relation to other types of tumor in which DNA coating around blood vessels has been observed. It would appear that tumor necrosis and cell death are crucial factors that may lead to DNA precipitation in a variety of forms.