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C. J. Connon, A. Hopkinson, T. Nakamura, J. Doutch, S. Kinoshita, K. M. Meek; The Variation in Transparency of Amniotic Membrane Used in Ocular Surface Regeneration. Invest. Ophthalmol. Vis. Sci. 2007;48(13):455.
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© ARVO (1962-2015); The Authors (2016-present)
Human amniotic membrane (HAM) is increasingly used in ophthalmic surgery. Its use often results in the post operative positioning of HAM within the visual field. Presently there is little consideration given to the variation in membrane structure at source or to the significance that these differences might have on its clinical transparency. Therefore, we applied our experience of quantifying corneal transparency to the transparency of HAM.
HAM was prepared in accordance with a previously published procedure(1). HAM samples (n=3) were dissected from areas proximal, mid-point and distal to the placental margin, cut into 5 cm squares, washed in phosphate buffered saline (PBS, pH 7.2), and stored at -80ºC. The chorion layer was removed from half the samples before freezing(2). The frozen samples were defrosted and their epithelium removed by scrapping (denuded). Denuded freeze dried HAM(3) (n=3) were also included in the study. The percentage transmission of visible light (400-700nm) was measured from freeze dried and freeze preserved HAM samples (+ and - chorion) in PBS using an SP8-100 UV/Vis spectrophotometer. The samples were then fixed for light microscopy and transmission electron microscopy to measure tissue thickness and collagen arrangement.
Percent transmission differed significantly between the 3 areas of HAM investigated. Percent transmission increased as the distanced increased from the placental margin and as the samples became thinner. The removal of the chorion layer only increased transmission in samples taken distal to the placental margin. However freeze dried HAM had the highest percent transmission; these samples were also the thinnest. Light and transmission electron microscopy revealed a strong correlation between HAM thickness and transparency, furthermore when normalized against thickness, HAM was calculated to be 85% as transparent as the human cornea (using direct summation of fields method(4))
Using HAM for ocular surface reconstruction within the visual field, tissue taken from an area of the amniotic sac distal to the placenta offers the most transparency; furthermore removal of the chorion from this tissue significantly increases its transparency. However, freeze dried HAM offers the most transparency.1. Tsubota K et al. AJO 19992. Hopkinson A et al. IOVS 20063. Nakamura T et al. IOVS 20044. Freund DE et al. IOVS 1995
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