Distribution of Fluorescence in the Human Cataractous Lens

Augusteyn, Robert C.

doi:10.1159/000264754

Cited by 64 publications

(26 citation statements)

References 7 publications

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“…Circumstantial evidence indicates that chronic exposure of human eyes to ambient near-UV radiation may cause photocatalyzed reactions that initiate the formation of nuclear senile cataract with a concomitant production of fluorescent chromophors (5)(6)(7)(8). The examples of these reactions are the photooxidation of tryptophan (9,10) and the generation of singlet oxygen by UV and photosensitizers endogenous to the human lens (11).…”

mentioning

confidence: 99%

Automated laser-scanning-microbeam fluorescence/Raman image analysis of human lens with multichannel detection: evidence for metabolic production of a green fluorophor.

Cai²,

Ho³

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

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A laser-microprobe fluorescence/Raman spectrometer with a 700-channel detector has been constructed and applied to the collection of data on the distribution of a green fluorophor throughout the exposed area ofa human lens sectioned along the visual axis. The area ("'6.5 X 9.5 mm) covering the lens section was scanned automatically by the microprobe programmed to measure the fluorescence intensity at 1200 data points. The spectrometer output was accumulated in a microcomputer and displayed as a three-dimensional perspective view showing the fluorescence intensity at each point on the grid. The method permits the precise and detailed mapping at high resolution of the spatial distribution of a fluorophor or Ramanemissive constituent in a plane ofthe frozen lens to give results not obtainable by any other feasible procedure. The green fluorophor (441.6 nm, excitation wavelength; 520 nm, peak emission wavelength) has a distribution indicating a metabolic rather than a photochemical mode of production. Moreover, the lower level of fluorophor in the anterior segment suggests the existence of mechanisms in the anterior cortex (including the epithelium) that reduce significantly the accumulation of fluorophor. Such distribution studies are invaluable in clarifying metabolic interrelationships among the different zones of the lens, including especially photochemical reactions postulated to involve the effect of daylight on the lens in human subjects.The application of fluorescence and Raman spectroscopy to human and animal lenses has yielded information on the intact living lens that is hardly obtainable by other means (1, 2). We herein describe a greatly modified system that presents several advantages over our previous procedure that required the excitation beam to penetrate the lens at least to the zone where the emission originated. The system scans the surface of a frozen lens section and is, therefore, not affected by opaque regions in the body of the lens; this is a great advantage for cataract research.Our fluorescence/Raman imaging system has a number of important capabilities: (i) multichannel detection of "position-defined" fluorescence/Raman spectra from gridded points (1-8 ,um); (it) scanning of micro (10 ,um x 10 ,um) and macro (2.5 cm x 2.5 cm) samples; (iii) automated simultaneous acquisition of intensity data of up to six spectral lines (either peak or integrated intensities) from each point; (iv) excellent stray-light rejection to allow detection of weak Raman lines from solid samples; (v) normalization of fluorescence intensity with Raman signals (fluorescence/Raman intensity ratio); and (vi) presentation of the x-y data set in three-dimensional perspective, three-dimensional perspective with cursor-sectioning, six-color map representing regions of various intensity intervals, and topographic contour map with lines intersecting the intensity data with constant height intensity planes.We here describe how it has been employed to make fluorescence intensity measurements from a human lens section ...

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mentioning

confidence: 99%

Automated laser-scanning-microbeam fluorescence/Raman image analysis of human lens with multichannel detection: evidence for metabolic production of a green fluorophor.

Cai²,

Ho³

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

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“…This article must therefore be hereby marked "advertisement" in accordance with 18 (11). Four fractions were taken for racemization analyses.…”

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confidence: 99%

Aspartic acid racemization in heavy molecular weight crystallins and water insoluble protein from normal human lenses and cataracts.

Masters¹,

Bada²,

Zigler³

1978

Proc. Natl. Acad. Sci. U.S.A.

117

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High D/L aspartic acid ratios are observed in heavy molecular weight aggregates and in water-insoluble protein extracted from whole lenses and nuclear and cortical regions. Purified a-, A-, and -y-crystallins have low D/L ratios. Fractionation of urea-solubilized material from the water-insoluble protein yields four molecular weight classes of proteins. Fractions representing crosslinked material or apparently degraded products have high D/L ratios. Racemization within lens proteins may contribute to formation of the water-insoluble fraction seen in aging lenses and cataracts. The racemization of aspartyl residues has recently been added to the list of age-related changes taking place in the proteins of the human lens (1). D-Aspartyl residues have been shown to accumulate at the rate of 1.25 X 10-3 yr-1 or 0.14% yr-1 in the central nucleus. The extent of racemization in yellow cataracts is equivalent to that observed in age-matched normal lenses, but brunescent cataracts exhibit up to a 2-fold increase in D/L aspartic acid ratios over comparably aged normal lenses or yellow cataracts.The rationale for investigating lens proteins came from our studies of calcified proteins in human teeth (2, 3). Detectable amounts of D-aspartic acid accumulate during the human lifespan as a result of the spontaneous chemical racemization reaction. These findings suggested that the aspartyl residues in any metabolically stable protein maintained at mammalian body temperature for several decades or longer would be subject to racemization. Because the proteins in the nucleus of the human lens are among the most stable in the body, we decided to test our hypothesis with the lens system.Numerous studies have shown that structural changes are taking place in lens proteins during the normal aging process and in cataracts. The proportion of water-insoluble protein increases relative to water-soluble protein (4, 5). The increase of insoluble protein is more marked in cataracts (6). When the water-insoluble residue is extracted with 7 M urea, the ureainsoluble portion is greater in cataracts (6) and is derived primarily from the lens nucleus (7). There is some evidence that more exposed thiol groups occur in cataractous proteins, and these proteins may have a greater susceptibility to tryptic digestion (8). All of these observations indicate that changes in native conformation of the lens proteins are occurring in cataract development and in aging.We have previously suggested that alterations in protein conformation will result from racemization of aspartyl residues (9). If racemization is to any degree responsible for the changes in the properties of lens proteins, then D-aspartic acid should

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“…That is followed by fluctuation in the protein content and thereby in the refractive index which increases the light scatter (Philipson 1973;Duncan et al 1989Duncan et al , 1997. In nuclear cataract, there is increase in selective spectral absorption, in pigmented chromophores and in cross-linked protein aggregates found in the nuclear region (Philipson 1973;Augusteyn 1975). It has been proposed that the decreased transmission of visible light in the aging lens and in nuclear cataract is mainly due to the accumulation of lens fluorogens rather than configurational changes of the lens pro-teins as seen in cortical cataracts (Lerman & Borkman 1976).…”

Section: Discussionmentioning

confidence: 99%

“…The lens fluorogens are responsible to a significant degree for the increasing yellow coloration of the lens with age (Augusteyn 1975;Lerman & Borkman 1976). We have developed a technique to measure blue-green autofluorescence (AF) of the lens and showed that it increases with age and with the degree of nuclear cataract (Siik et al 1991(Siik et al , 1993.…”

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confidence: 99%

Lens autofluorescence and light scatter in relation to the lens opacities classification system, LOCS III

Siik

Chylack

Friend

et al. 1999

Acta Ophthalmologica Scandinavica

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ABSTRACT.Purpose: To compare values of the human lens autofluorescence and back light scatter measurements with the improved Lens Opacities Classification System, LOCS III. Methods: We measured autofluorescence and back light scatter of the lens from 122 smoking males aged 57 to 76 years who participated in a cancer prevention study. The retroillumination and slit-lamp photographs of the lenses were graded according to LOCS III by the Center for Ophthalmic Research in Boston. Lens fluorometry was carried out with a previously described technique using bluegreen (495 nm/520 nm) autofluorescence range. Interzeag Lens Opacity Meter 701 was used for light scatter measurements. Results: LOCS III nuclear opalescence and color grades were statistically significantly correlated with lens autofluorescence as well as with light scatter values. The lens transmission index of autofluorescence measurements showed the highest correlation with the nuclear color (rΩª0.71; p∞0.0001) and the light scatter value with nuclear opalescence (rΩ0.64; p∞0.0001). There was no correlation between autofluorescence measurements and LOCS III grades of cortical or posterior subcapsular cataract. A weak relation could be found between the grades of cortical cataract and light scatter values. Conclusions:The lens fluorometry provides a practical clinical technique to evaluate the yellow coloration and opalescence of the human lens nucleus. It may be a useful additional tool together with a subjective grading system in the follow-up of optical changes occurring in the nuclear region of the lens.

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Distribution of Fluorescence in the Human Cataractous Lens

Cited by 64 publications

References 7 publications

Automated laser-scanning-microbeam fluorescence/Raman image analysis of human lens with multichannel detection: evidence for metabolic production of a green fluorophor.

Automated laser-scanning-microbeam fluorescence/Raman image analysis of human lens with multichannel detection: evidence for metabolic production of a green fluorophor.

Aspartic acid racemization in heavy molecular weight crystallins and water insoluble protein from normal human lenses and cataracts.

Lens autofluorescence and light scatter in relation to the lens opacities classification system, LOCS III

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