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M. J. Costello, K. O. Gilliland, S. Metlapally, B. Ramamurthy, P. V. Krishna, D. Balasubramanian; Ultrastructural Analysis of Damage to Nuclear Fiber Cell Membranes in Advanced Cataracts From India. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4211.
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To characterize the structural alterations at nuclear fiber cell interfaces in fully opaque cataracts removed by extracapsular cataract surgery in India.
Fourteen nuclei from advanced cataracts graded 3, 4, or totally opaque by clinicians were examined with the Vibratome sectioning method used previously. The dark yellow to nearly black nuclei, ages 38-78, were probably representative of advanced age-related nuclear cataracts. Thick tissue slices were fixed and embedded for transmission electron microscopy. Thin sections were stained and examined with a Tecnai 12 electron microscope employing a digital camera and tilt stage to bring membranes and junctions into clear view.
Membrane damage was noted in all regions of the nucleus. The most important damage occurred within undulating membrane junctions where the loss of membrane segments was common. These membrane breaks were not sites of fusion as membrane edges were detected and cytoplasm was exposed to extracellular space (ECS). The ECS, bordered by well-preserved single membranes, was enlarged in many regions. Within the ECS, dense deposits of protein-like material was frequently observed and appeared to be more uniformly stained than adjacent cytoplasm. The ECS deposits were often 20-50 nm thick and variable in length. In addition, low-density regions were seen within the ECS and between the cytoplasm and the plasma membranes. These spaces may be produced by contraction of the cytoplasm during age-related fiber cell compaction, protein aggregation and loss of cytoplasmic crystallins and fragments. The spaces in some regions within highly undulating membranes were about 100 nm in diameter. The membrane damage was more extensive than in aged transparent donor lenses. All lenses showed many sites of membrane contact at gap junctions and junctions probably containing AQP0.
Because high and low density regions contribute equally to the fluctuations in refractive index, the changes in density due to the observed damage near membranes probably produce significant light scattering. The dimensions of the fluctuations in the range 20-100 nm implies that the scattering is probably similar to small particles that would increase high-angle scattering visible in the slit lamp. Such damage to membranes would be expected to contribute to the total opacification of the nucleus as the cataract matures. The main sources of the fluctuations appear to be the degradation of membranes and cytoplasmic proteins, as well as the redistribution of proteins and fragments.
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