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CD Freel, KO Gilliland, FJ Giblin, MJ Costello; Morphological Characterization of the Hyberbaric Oxygen Treated Guinea Pig Model by TEM Aanalysis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2359.
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Purpose: Determine the structural characteristics of differentiated fiber cells in control and hyperbaric oxygen (HBO) treated guinea pig lenses by transmission electron microscopy (TEM). Emphasis was placed on cell damage, cytoplasmic texture, and membrane integrity. Given the faint gross opacities observed in HBO-treated lenses in previous studies, it was hypothesized that subtle but significant morphological differences due to oxidative damage exist between control and treated animals. Methods: Eyes from control and HBO-treated (Giblin et al., Exp. Eye Res., 1995, 60:219-35) guinea pigs were obtained within 24 hours death. Experimental animals received approximately 70 treatments with HBO over a six-month period (2.5 atm of 100% O2 for 2.5 hours, 3 times per week). Freshly cut Vibratome lens sections were fixed and processed for low and high-magnification thin-section TEM analysis. Cytoplasmic texture was analyzed using Fourier and autocorrelation image processing techniques. Results: Low-magnification analysis revealed relatively insignificant differences in general appearance between the fiber cells of the inner fetal and embryonic nuclei in control and HBO-treated guinea pigs. Both groups demonstrated cells of similar morphology with homogeneous cytoplasmic texture and equivalent membrane complexity. Evidence of any major cellular damage or extracellular space debris was not obvious. At higher magnifications the cytoplasm of the treated lenses exhibited a mild increase in texture compared with controls, almost undetectable by eye. Fourier analysis of the treated cytoplasm revealed a slightly larger peak area in the 100 nm and greater subunit region of the transforms compared with controls, confirming the slight increase in texture. Differences in membrane integrity were also detectable. Conclusion: The lack of major cellular damage in the lenses of HBO-treated animals suggests a less conspicuous source of light scattering. It is possible that the mild scattering observed by slit-lamp in the lens nucleus of treated guinea pigs may be entirely attributed to small, yet measurable increases in cytoplasmic texture as detected by Fourier and autocorrelation analyses. The observed changes in membrane structure due to oxidation may also contribute to the scattering. This sort of high-angle scattering due to HBO treatment may represent the cytoplasmic reorganization that occurs with mild oxidation, effectively making the HBO-treated guinea pig a valuable model for human lens aging.
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