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Identification of silicone oil in ocular tissues
  1. A Ohira
  1. Correspondence to: A Ohira 89-1, Shimane University School of Medicine, Izumo, 693-8501, Japan; aohiramed.shimane-u.ac.jp

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I read with interest the article by Miyamoto et al.1 Numerous studies have examined the inter-relation between silicone oil and various ocular structures, such as the retina, iris, or anterior chamber. However, the silicone oil itself was never evident in these studies, but rather small vacuoles suspected to be ghosts of the incorporated silicone oil were apparent. Nevertheless, the vacuoles also could have been artefacts2 because silicone, which is solubilised in the organic solvents during the preparation,3 is never detected. We previously demonstrated silicone oil emulsion in the rabbit retina using phthalocyanine blue as a marker.4 This compound contains a copper molecule that imparts a blue colour and remains in the tissue after the silicone oil is washed out and enables visualisation of the silicone emulsion in the trabecular meshwork at the light and electron microscopic levels. When we injected a suspension of the dye into the anterior chamber, the dye filled the small vacuoles within the cells. In contrast, when silicone droplets containing the dye were injected into the chamber, the blue dye formed clusters in small cellular vacuoles (light microscopy) and touched the limiting membranes of the vacuoles (electron microscopy). The silicone droplets were washed out by the organic solvents used to prepare the specimens, and since the dye was insoluble in the organic solvent, it probably precipitated around the vacuoles.5 However, figure 5 of this article did not show any limiting membranes or the low magnification of this figure precluded their identification. In addition, energy dispersive x ray analysis is also a useful method to detect silicone oil in tissues.6

The authors injected silicone oil that was not emulsified into the vitreous cavity after vitrectomy. However, silicone oil that is not emulsified has a large surface area and high interfacial surface tension and is not incorporated into the tissues. The authors did not show by gross examination whether silicone oil became emulsified during the experiment. They should discuss why they could see residual silicone oil in the rest of the anterior capsule. The readers were not able to obtain information about silicone oil structure. Although the authors described emulsification of silicone oil related to protein, many factors are involved in this process. Contamination of low molecular weight siloxanes may enhance silicone oil emulsification.

In the discussion, the authors state: “It is likely that lens epithelial cells attaching to oil droplets might be stimulated to express many wound healing related molecules including extracellular matrix components.” This is speculation. The central area of the posterior surface of the rest of the anterior capsule is covered with accumulated fibrous extracellular matrix in figures 2B and 4B. However, there were no differences in the expression of collagen types I, III, V, and cellular fibronectin by immunohistochemistry. The authors did not provide these data in the text. If this information is related to their hypothesis, they should demonstrate differences by providing immunohistochemical data.

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