Biometric, optical and physical changes in the isolated human crystalline lens with age in relation to presbyopia.
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The biometric, optical and physical properties of 19 pairs of isolated human eye-bank lenses ranging in age from 5 to 96 years were compared. Lens focal length and spherical aberration were measured using a scanning laser apparatus, lens thickness and the lens surface curvatures were measured by digitizing the lens profiles and equivalent refractive indices were calculated for each lens using this data. The second lens from each donor was used to measure resistance to physical deformation by providing a compressive force to the lens. The lens capsule was then removed from each lens and each measurement was repeated to ascertain what role the capsule plays in determining these optical and physical characteristics. Age dependent changes in lens focal length, lens surface curvatures and lens resistance to physical deformation are described. Isolated lens focal length was found to be significantly linearly correlated with both the anterior and posterior surface curvatures. No age dependent change in equivalent refractive index of the isolated lens was found. Although decapsulating human lenses causes similar changes in focal length to that which we have shown to occur when human lenses are mechanically stretched into an unaccommodated state, the effects are due to nonsystematic changes in lens curvatures. These studies reinforce the conclusion that lens hardening must be considered as an important factor in the development of presbyopia, that age changes in the human lens are not limited to the loss of accommodation that characterizes presbyopia but that the lens optical and physical properties change substantially with age in a complex manner. (+info)
Light scattering model for donor lenses as a function of depth.
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The amount of light scattered by normal donor lenses (n = 15, ages 43-82 years) from a 1 x 0.1 mm white slit beam was measured as a function of depth in the lens for seven angles from 10 to 165 degrees, and for four wavelengths from 400 to 700 nm. Apart from the most superficial layers, the data could be described with a model that consisted of three components. (1) small sized protein particles (alpha-crystallin), (2) large sized protein particles and (3) spectrally neutral rough surface reflectance ('zones of discontinuity'). Component (1) and (3) dominate backward scattering. Component (2) dominates forward scattering, but occupies only around 0.000006 of the lens volume, with the lowest values in the nucleus. Component (3) is important for a small range of backward directions only, being much stronger in extranuclear areas than in the nucleus. (+info)
Optics of the developing fish eye: comparisons of Matthiessen's ratio and the focal length of the lens in the black bream Acanthopagrus butcheri (Sparidae, Teleostei).
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Matthiessen's ratio (distance from centre of lens to retina:lens radius) was measured in developing black bream, Acanthopagrus butcheri (Sparidae, Teleostei). The value decreased over the first 10 days post-hatch from 3.6 to 2.3 along the nasal and from four to 2.6 along temporal axis. Coincidentally, there was a decrease in the focal ratio of the lens (focal length:lens radius). Morphologically, the accommodatory retractor lentis muscle appeared to become functional between 10-12 days post-hatch. The results suggest that a higher focal ratio compensates for the relatively high Matthiessen's ratio brought about by constraints of small eye size during early development. Combined with differences in axial length, this provides a means for larval fish to focus images from different distances prior to the ability to accommodate. (+info)
Mechanics of accommodation of the human eye.
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The classical Helmholtz theory of accommodation has, over the years, not gone unchallenged and most recently has been opposed by Schachar at al. (1993) (Annals of Ophthalmology, 25 (1) 5-9) who suggest that increasing the zonular tension increases rather than decreases the power of the lens. This view is supported by a numerical analysis of the lens based on a linearised form of the governing equations. We propose in this paper an alternative numerical model in which the geometric non-linear behaviour of the lens is explicitly included. Our results differ from those of Schachar et al. (1993) and are consistent with the classical Helmholtz mechanism. (+info)
O-Crystallin, arginine kinase and ferritin from the octopus lens.
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Three proteins have been identified in the eye lens of the octopus, Octopus dofleini. A 22 kDa protein comprising 3-5% of the soluble protein of the lens is 35-43% identical to a family of phosphatidylethanolamine-binding proteins of vertebrates. Other members of this family include the immunodominant antigen of the filarial parasite, Onchocerca volvulus, putative odorant-binding proteins of Drosophila and a protein with unknown function of Caenorhabditis elegans. We have called this protein O-crystallin on the basis of its abundance in the transparent lens. O-Crystallin mRNA was detected only in the lens. Two tryptic peptides of another octopus lens protein, less abundant than O-crystallin, showed 80% identity to arginine kinase of invertebrates, a relative of creatine kinase of vertebrates. Finally, ferritin cDNA was isolated as an abundant cDNA from the octopus lens library. Northern blots showed that ferritin mRNA is not lens-specific. (+info)
alpha6 Integrin is regulated with lens cell differentiation by linkage to the cytoskeleton and isoform switching.
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The developing chicken embryo lens provides a unique model for examining the relationship between alpha6 integrin expression and cell differentiation, since multiple stages of differentiation are expressed concurrently at one stage of development. We demonstrate that alpha6 integrin is likely to mediate the inductive effects of laminin on lens differentiation as well as to function in a matrix-independent manner along the cell-cell interfaces of the differentiating cortical lens fiber cells. Both alpha6 isoform expression and its linkage to the cytoskeleton were regulated in a differentiation-specific manner. The association of alpha6 integrin with the Triton-insoluble cytoskeleton increased as the lens cells differentiated, reaching its highest levels in the cortical fiber region where the lens fiber cells are formed. In this region of the lens alpha6 integrin was uniquely localized along the cell-cell borders of the differentiating fiber cells, similar to beta1. alpha6beta4, the primary transmembrane protein of hemidesmosomes, is also expressed in the lens, but in the absence of hemidesmosomes. Differential expression of alpha6A and alpha6B isoforms with lens cell differentiation was seen at both the mRNA and the protein levels. RT-PCR studies demonstrated that alpha6B was the predominant isoform expressed both early in development, embryonic day 4, and in the epithelial regions of the day 10 embryonic lens. Isoform switching, with alpha6A now the predominant isoform, occurred in the fiber cell zones. Immunoprecipitation studies showed that alpha6B, which is characteristic of undifferentiated cells, was expressed by the lens epithelial cells but was dramatically reduced in the lens fiber zones. Expression of alpha6B began to drop as the cells initiated their differentiation and then dropped precipitously in the cortical fiber zone. In contrast, expression of the alpha6A isoform remained high until the cells became terminally differentiated. alpha6A was the predominant isoform expressed in the cortical fiber region. The down-regulation of alpha6B relative to alpha6A provides a developmental switch in the process of lens fiber cell differentiation. (+info)
Pax-6 interactions with TATA-box-binding protein and retinoblastoma protein.
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PURPOSE: To identify proteins that physically interact with Pax-6, a paired domain- and homeodomain (HD)-containing transcription factor that is a key regulator of eye development. METHODS: Protein-protein interactions involving Pax-6, TATA-box-binding protein (TPB), and retinoblastoma protein were studied using affinity chromatography with Pax-6 as ligand, glutathione-S-transferase (GST) pull-down assays, and immunoprecipitations. RESULTS: The authors have shown that Pax-6 is a sequence-specific activator of many crystallin genes, all containing a TATA box, in the lens. Others have shown that lens fiber cell differentiation, characterized by temporally and spatially regulated crystallin gene expression, depends on retinoblastoma protein. In the present study it was shown that Pax-6 interacted with the TBP, the DNA-binding subunit of general transcription complex TFIID. GST pull-down assays indicated that this interaction was mediated by the Pax-6 HD, with a substantial role for its N-terminal arm and first two alpha-helices. The experiments also indicated a binding role for the C-terminal-activation domain of the protein. In addition, the present study showed that the HD of Pax-6 interacted with retinoblastoma protein. Immunoprecipitation experiments confirmed retinoblastoma protein/Pax-6 complexes in lens nuclear extracts. CONCLUSIONS: Blending the present results with those in the literature suggests that Pax-6 and retinoblastoma protein participate in overlapping regulatory pathways controlling epithelial cell division, fiber cell elongation, and crystallin gene expression during lens development. (+info)
Exogenous gene expression and protein targeting in lens fiber cells.
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PURPOSE: To test the ability of lens fiber cells at various stages of differentiation to transcribe and translate microinjected DNA templates. METHODS: Expression plasmids encoding green fluorescent protein (GFP) or a GFP-tagged membrane protein (human CD46) were microinjected into organ-cultured embryonic chicken lenses. Protein expression was visualized by confocal microscopy. RESULTS: GFP expression was detected within 12 hours of microinjection, evenly distributed throughout the cytoplasm of the injected cell. All nucleated fiber cells were competent to express GFP, whereas the anucleated central fiber cells were not. When GFP was fused to the C-terminal of CD46, the fusion protein was synthesized intact and properly inserted in the fiber cell plasma membrane. In contrast, N-terminal fusions were cleaved during synthesis, resulting in retention of the GFP tag in the endoplasmic reticulum. CONCLUSIONS: Microinjection of expression plasmids is an effective technique for introducing exogenous genes into individual fiber cells. With this approach, the results show that fiber cells are transcriptionally and translationally competent until the time of organelle loss, and that fiber cells deep within the lens are capable of synthesizing new plasma membrane proteins. The techniques described here should have broad application in studies of fiber cell differentiation and provide a useful complement to conventional transgenic approaches. (+info)