Brunescent Cataract Research Articles

Scanning EM studies of normal human lens fibres and fibres from nuclear cataracts

Normal human lenses obtained from an eye bank, and the central nuclear regions from nuclear sclerotic cataracts, were examined using scanning electron microscopy. Lens fibres were found to possess a varied array of well defined interlocking processes. Fibres from brunescent nuclear cataracts showed complete preservation of membrane architecture in contrast to the extensive membrane disruption that has been seen in cortical cataracts.

Senile Lens Exfoliation

An 86-year-old man complained of decreasing vision in his left eye. He has had poor vision in his right eye since he was a child. Visual acuity was counting fingers at 1 ft OD and 20/60 OS. Slit-lamp examination revealed bilateral brunescent cataracts. Also present bilaterally was a thin, clear membrane that protruded through the pupil to float in the anterior chamber. The membrane was attached to the anterior lens capsule and was best seen with retroillumination (Fig 1). The patient denied any history of ocular trauma or occupational exposure to excessive heat or infrared radiation. He underwent uneventful extracapsular cataract extraction with posterior chamber intraocular lens implantation in his left eye. The anterior lens capsule was sent for analysis. Histopathologic examination revealed an eosinophilic amorphous substance with a periodic acid-Schiff—positive membrane. At high magnification the membrane showed multiple splitting of the anterior lens capsule (Fig 2). True lens exfoliation

Ocular hazards arising from depletion of the natural atmospheric ozone layer: a review*

The processes contributing to the maintenance of the natural, atmospheric, ozone layer, which screens the earth's surface from solar ultraviolet radiation at wavelengths below 300 nm, are described. The possible adverse effects of man-made chemicals such as chlorofluorocarbons (CFCs) on this layer are outlined. Consideration of the flux of ultraviolet light reaching the earth's surface as a function of the ozone concentration and other factors allows the effect of ozone changes on ocular health to be evaluated. It is concluded that the changes of the order of a few per cent that are predicted by current models of the atmosphere, and which are comparable with natural fluctuations in ozone, would have relatively little effect on the incidence of solar keratitis at the cornea. Larger changes, in the order of 50%, would be expected to have a significant effect. There might also be an increase in the incidence of brunescent cataract. Ozone changes would have a negligible effect on the amounts of solar radiation reaching the retina.

Zur Wertigkeit der Rot-Grün-Teste

The causes of chromatic aberration were elucidated by Newton in 1704, though in regard to the eye the phenomenon has been a subject of controversy. The chromatic aberration of the eye has long been used to determine refraction. In principle, blurred coloured circles are visible which depend on the chromatic aberration of the eye and lead to perception of different contrasts in the dark optotypes presented in the two coloured fields, depending on the real ametropia or correction conditions. Uniform perception of contrast by the subject is used as the criterion for correction. As regards the red-green test, it appears doubtful that the results are not influenced by protanopia and brunescent cataract. Therefore, the contrast thresholds of 8 protanopic patients and 5 patients with brunescent cataract were examined. This was done using special red and green lenses (produced by VEB Carl Zeiss Jena) under individual conditions with Landolt's rings. Characteristic differences in the contrast thresholds for red and green were found. For bichromatic tests no procedure has been defined, and neither the wave-lengths to be used nor the reference wavelength have been laid down. The results can be affected by numerous physical, physiological and pathological factors. The accuracy and practical usefulness of red-green tests are questionable. Therefore, it does not appear justified to equip ophthalmological examination instruments for such tests.

Activities of ascorbate free radical reductase and H 2O 2-dependent NADH oxidation in senile cataractous human lenses

Changes in activities of ascorbate free radical (AFR) reductase (NADH: AFR oxidoreductase) and H 2O 2-dependent NADH oxidation were correlated with levels of insoluble protein in senile cataractous human lenses. The H 2O 2-dependent NADH oxidation activity was measured to reflect the content of free glutathione. AFR reductase activities in all the cataractous lenses assayed here tended to decrease with increase of insoluble protein contents. A similar tendency in the relationship between lens protein aggregation and H 2O 2-dependent NADH oxidation activities, i.e. free glutathione contents was recognized in the lenses with pale yellow, yellow or dark yellow nucleus. However, for the highest levels of insoluble protein, some of the brunescent cataractous lenses exhibited very high activities of H 2O 2-dependent NADH oxidation, and some brunescent lenses had very low activities. From the above results, it is suggested that lens protein aggregates in the brunescent and non-brunescent cataractous lenses may be formed through significantly different oxidation processes, respectively. The possible mechanisms such as free radical reaction and disulfide bond formation are discussed.

A Unilateral Cataract Produces a Relative Afferent Pupillary Defect in the Contralateral Eye

The relative afferent pupillary defect (RAPID) was measured with neutral density filters in ten patients, each of whom had a dense cataract in one eye only. In each instance, the cataract reduced visual acuity to counting fingers or worse, whereas visual acuity in the other eye was 20/25 or better. All patients with mature or nuclear cataracts had a measureable RAPID in the other eye (mean, 0.44 log unit). In each instance, after extraction of the cataract, the RAPID disappeared. Thus, a dense cataract causes an RAPID in the contralateral eye by increasing the pupillomotor effectiveness of the stimulus light and that this is the reason why even a brunescent cataract does not cause an RAPID in the same eye. In addition, two clinical cases are reported. One case records the development of a cataract in an eye with a preexisting RAPID resulting from optic neuritis; as the cataract became more opaque, the afferent defect became smaller and finally was reversed. The other case shows that a traumatic cataract can produce an RAPID in the contralateral eye. Thus, when an afferent pupillary defect is seen in an eye with a cataract, a visual pathway defect in that eye should definitely be suspected.

Mechanism of Coloration of Human Lenses Induced by Near-Ultraviolet-Photo-Oxidized 3-Hydroxykynurenine (With 1 color plate)

Tha absorption spectra of human cataractous lenses, classified into four groups on the basis of coloration, were measured by a spectrophotometer equipped with an integrating sphere that is able to detect diffuse reflectance of solid materials. The results revealed that pale-yellow cataractous lenses showed a characteristic absorption spectrum with a peak near 365 nm, coincident with that of 3-hydroxykynurenine, and that brunescent cataractous lenses with high pigmentation showed an absorption spectrum with a peak over 400 nm, coincident with that of xanthommatin, a dimerized compound of 3-hydroxykynurenine. Depending on the coloration of the lens, the position of maximum absorption shifted from 365 to 410 nm and the optical density increased at visible regions. The changes in absorption spectra of pale-yellow lens homogenates were studied in the presence or absence of 3-hydroxykynurenine and by near-ultraviolet (UV) irradiation. Brown pigments were formed in the insoluble proteins of lens homogenates by 48 h of exposition of the samples with 3-hydroxykynurenine to UV irradiation. The absorption spectra of the brown pellets detected by an integrating sphere corresponded well to those of pellets which were obtained from the homogenates of intact human brunescent cataractous lenses. These results strongly suggest that 3-hydroxykynurenine and UV irradiation are involved in the brown pigmentation of human cataractous lenses by formation of xanthommatin.

The effects of aging and cataract formation on the trypsin inhibitor activity of human lens

Assays were carried out to determine the trypsin inhibitor activity present in the water-soluble and water-insoluble fractions of human lenses of various ages. Little change was seen in the inhibitor activity of the water-soluble protein fraction. When this fraction was chromatographed on an Agarose A-1·5 m column, however, the inhibitor activity was increasingly associated with the high molecular weight (HMW) protein fraction with age. A gradual increase in water-insoluble inhibitor was seen up to age 60, which correlated with the increase in protein in this fraction. After age 60, a marked increase in the water-insoluble inhibitor activity was observed. In 80–90-yr-old lenses. 1 mg of water-insoluble protein was able to inhibit 200 μg of crystallin trypsin by 50%. Similar assays on a collection of cortical and brunescent cataracts also showed very high levels of water-insoluble inhibitor activity. In most cases, these values were higher than those for age-matched control lenses. Fractionation of the water-insoluble proteins showed that the bulk of the activity remained with the urea-insoluble fraction in cataractous lenses. A low molecular weight trypsin inhibitor was isolated from the water-soluble and water-insoluble fractions of human lenses. An age-dependent increase in this inhibitor was observed by activity measurements and electrophoretic analysis.

Spectroscopic studies of brunescent cataractous lenses

The absorption spectra of brunescent cataractous lenses and their homogenates were analyzed under various conditions by using a double wavelength spectrophotometer. The absorption spectra of the samples were in good agreement with those of synthetic xanthommatin derived from 3-hydroxykynurenine. The results provided evidence that brown pigment in the brunescent cataractous lenses is mainly composed of xanthommatin.

Lipids of human lens fiber cell membranes.

A study of the membranes of human lens fiber cells revealed a very high protein to lipid ratio, which tended to increase with aging and in brunescent cataract. Phospholipids were more abundant than cholesterol, cholesterol esters, and other neutral lipids. With aging and cataract formation, a marked decrease in membranes phospholipid content occurred. Sphingomyelin was present in highest amount. Phosphatidylethanolamine, phosphatidylcholine, lysophosphatidyl-ethanolamine, phosphatidylserine, and phosphatidylglycerol were also present. Cholesterol represented approximately 40% of the total lipids. Saturated and unsaturated fatty acids having 16 to 24 carbons were present. The lipid composition varied according to the portion of the lens examined and the state of the lens. The results do not support a conclusion that lipid peroxidation represents a major mechanism of membrane damage that contributes to cataract formation, since there is no decrease in unsaturated fatty acids with age or in cataractous lenses. We suggest that the aggregation of soluble proteins, and their association with lens membranes, and altered membrane function due to the loss of phospholipids are important processes leading to loss of transparency.

Presence of low molecular weight polypeptides in human brunescent cataracts

Microdissected sections from opaque & brunescent lens nuclei contain low molecular weight (4,000–8,000 dalton) polypeptides not found in microdissected sections of transparent lens nuclei. Tryptic digestion of these polypeptides from different cataracts reveal similar peptide maps. Together, these results support the involvement of proteolysis in human cataractogenesis, and suggest the possibility of similar molecular mechanisms occuring in cleavage of lens polypeptides during formation of the opaque & brunescent human cataract.

Glutathione content of the lens in various forms of cataract

Both the electrolyte ratio (K greater than Na) and high glutathione content of the lenses are generally undisturbed in the brunescent nuclear cataract (cataracta brunescens), the primary grey nuclear cataract, and the supranuclear cataract (senile cortical cataract). The electrolyte ratio (Na greater than K) and greatly decreased glutathione content are also grossly pathological in the subcapsular cataract (cataracta complicata, posterior subcapsular cataract), especially in connection with a secondary grey nuclear cataract, the mature cataract (cataracta matura), and the intumescent cataract. Alteration of the electrolyte concentrations and the glutathione content may be the results of physical, anatomical, and various metabolic disorders.

Calcium content and distribution in human cataract

The calcium content and distribution was measured in brunescent cataracts from India and cataracts from the United States classified according to guidelines of the Cooperative Cataract Research Group (CCRG). The severity and extent of opacification correlates well with the increase in Ca 2+ bound to membranes and insoluble proteins separated by differential centrifugation. Thus, bound Ca 2+ is approximately 30 ng/mg for the immature cataract. 100 ng/mg for the pale yellow. 200 ng/mg for the mature cataract and 300 ng/mg for the brown brunescent. These values can be compared to 16 ng/mg (0·2 m m) for a freshly excised rabbit lens. To the extent that the mature cataract represents an advanced stage and the immature cataract an early stage of development, and likewise for the brown and pale yellow cataract, results of this study suggest that cataract development is not accompanied by, or the result of, a redistribution of ‘free’ and bound calcium. We find that the fraction of total calcium bound to membranes and insoluble proteins is the same in the early and advanced stages of U.S. and Indian cataracts. It appears that as calcium accumulates in the developing cataract, an increasing amount becomes membrane or protein bound while the level of diffusible Ca 2+ continues to increase. In the advanced stage as much as 85% of the calcium in the 10 000 g supernatant is dialyzable or diffusible. The remaining 15% is bound to watersoluble proteins and represents a sixfold to 15-fold increase in the mature and brown cataract, respectively. There is also a considerable increase in the amount of calcium found in the 1000 g pellet containing insoluble proteins and membrane fragments.

Conservation of optical purity of amino acids: a principal problem in biochemical and proto-biochemical systems.

Dor L-amino acids, regardless of their state (peptide-bound or free, in the solid state or in aqueous solution), tend to racemize. In a living cell this racemization is usually compensated by specific degradation and replacement of the unwanted polypeptides that contain the wrong enantiomers. But a few long-lived proteins that are synthesized at or near birth are never replaced. Well investigated is the racemization of L-aspartic acid at a rate of 0.1 to 1.14 per cent per year in proteins from lenses and dentine. Increased racemization of eye lens proteins has been related to a form of human eye disease known as brunescent cataracts. Also quite well investigated is the racemization of amino acids in fossil proteins. The time and temperature dependence of racemizations has found various applications in the determination of the ages of long-lived individuals and in the investigation of the ages and the tempe<ature history of younger fossils. For prebiotic peptide synthesis no practicable mechanism that leads to the exclusion of the unwanted optical antipodes has as yet been found. Peptides (in particular dipeptides) in aqueous solution generally racemize about as fast as free amino acids. In thermal polymerization of amino acids racemization often proceeds faster than polymerization. Some new data on the racemization of amino acids during thermal peptide synthesis will be presented.

Ultraviolet radiation in the aging and cataractous lens. A survey.

An increase in the insoluble protein levels, in fluorescence, and a decrease in the SH concentration are three specific aging parameters in the mammalian lens. These can be markedly accelerated in human, rat and mouse lenses by in vitro exposure (for at least 4 h) to UV radiation (above 300 nm) and 3‐aminotriazole (AT) and in vivo by exposing mice to UV and parenteral AT for 4–6 weeks. UV, fluorescence, electron paramagnetic resonance (EPR) and Lasar Raman Spectroscopy were performed on normal and UV plus AT exposed 4–6 week old rat lenses and normal and experimental human lenses (1 day to 75 years of age). These data demonstrate the presence and/or induction of at least one fluorescent compound (fluorogen) (360 nm activation, 440 nm emission) derived from tryptophan by a free radical induced photooxidation reaction. Similar studies on purified lens proteins and peptides indicate that this fluorogen is tightly bound to at least one specific peptide. The age related increase in the concentration of fluorescent compounds enhances the yellowing of the lens core and accompanies polymerization of soluble protein precursors into the insoluble protein fraction. There is also a progressive fall in SH levels (with age or UV exposure) and an increase in SS bonds without any significant alteration in the secondary configuration of the lens proteins (which remain mainly in the anti‐parallel beta‐pleated configuration). It is postulated that UV radiation (300–380 nm) plays a role in lenticular aging, particularly nuclear sclerosis and its extreme state characterized by the Brunescent Cataract.

Normalizing effect of taurine on the lens permeability changes to rubidium due to phospholine iodide

Assays were carried out to determine the trypsin inhibitor activity present in the water-soluble and water-insoluble fractions of human lenses of various ages. Little change was seen in the inhibitor activity of the water-soluble protein fraction. When this fraction was chromatographed on an Agarose A-1·5 m column, however, the inhibitor activity was increasingly associated with the high molecular weight (HMW) protein fraction with age. A gradual increase in water-insoluble inhibitor was seen up to age 60, which correlated with the increase in protein in this fraction. After age 60, a marked increase in the water-insoluble inhibitor activity was observed. In 80–90-yr-old lenses. 1 mg of water-insoluble protein was able to inhibit 200 μg of crystallin trypsin by 50%. Similar assays on a collection of cortical and brunescent cataracts also showed very high levels of water-insoluble inhibitor activity. In most cases, these values were higher than those for age-matched control lenses. Fractionation of the water-insoluble proteins showed that the bulk of the activity remained with the urea-insoluble fraction in cataractous lenses. A low molecular weight trypsin inhibitor was isolated from the water-soluble and water-insoluble fractions of human lenses. An age-dependent increase in this inhibitor was observed by activity measurements and electrophoretic analysis.

The binding of photo-oxidized tryptophan to a lens gamma-crystallin

Some chemical properties of a photoproduct resulting from the near u.v. irradiation of tryptophan have been elucidated, and the manner in which this photoproduct binds to a bovine lens gamma-crystallin has been studied. Such binding alters absorption, fluorescence, electrical and solubility properties of this protein. Such a process may be involved in human lens browning and brunescent cataracts.

Spectral studies on normal and cataractous intact human lenses

Spectral characteristics are presented for intact normal and cataractous human lenses. By comparison with healthy intact lenses, no new spectral features (and therefore pigmentous species) are observed in brunescent cataract. However, in this cataract, a buildup in the components giving rise to high wavelength absorption (400–500 nm) is observed relative to that at lower wavelengths (∼ 300 nm). A model of protein tryptophan depletion via oxidation, resulting in protein pigmentation is considered, based on spectral evidence.