Extracapsular extraction of the crystalline lens]

Five subjects performed a maximal exercise test of repetitive lifting and lowering, with a discontinuous protocol of incremental exercise (3 min) and relative rest (2 min). Exercise periods consisted of repetitive lifting and repetitive lifting and lowering at increasing movement frequencies. Relative rest periods consisted of ergometer cycling at a constant, low power output. An unexpected, dissociated, response of cardiovascular and pulmonary parameters was found: during relative rest, values for oxygen uptake, carbon dioxide production, pulmonary ventilation and tidal volume were significantly higher than during the preceding exercise periods, though exercise intensity was much lower. To our knowledge, such a response has not been reported in previous studies. Since the response could not be attributed to methodological or technical factors, it is hypothesized that the type of exercise itself impeded the optimal performance of the oxygen transporting system. The function of the pulmonary system could have been influenced by a high intra-abdominal pressure, the involvement of respiratory muscles in stabilizing trunk and head, a flexed trunk posture and the entrainment of respiratory frequency with movement frequency. More likely, the function of the cardiovascular system was hindered by a high blood pressure and high intramuscular pressures. Since this response occurred at low exercise intensities, optimal functioning of the cardiovascular and pulmonary system during daily activities of repetitive lifting and lowering could similarly be impeded. The hypotheses put forward could also explain the lower peak oxygen uptake reported during repetitive lifting, compared to running and cycling.     

Scanning electron microscopic study of the development of crystalline lens fiber

Examines types of social support that best predicts adherence at different time points during a 1-year endurance exercise program in 269 women and men ages 50 to 65 years. Results indicate that social support had similar effects on exercise participation for women and men, and support specific to exercise was a better predictor of exercise adherence than general social support. A preference for receiving a lesser amount of initial support from exercise staff was the strongest social support-related predictor of exercise adherence during the initial 6 months of the program. Support currently received from family and friends and exercise staff at Month 6 was found to be the strongest predictor of adherence during Months 7 to 12. Format of exercise was also a strong predictor of exercise adherence with home-based programs related to greater adherence. Additionally, divorced nonsmokers appear to be at increased risk for poor early exercise adherence and should be targeted in interventions to promote exercise participation.     

Surgery on the crystalline lens. A plan of standardized care

In these days of concern for the growing costs of medical care it is an opportune moment to promote the importance of nurses as health care professionals and the roles that they play. This article presents a structural care plan for specific clinical situations regarding lens surgery with the goal of both guaranteeing quality nursing care and a method to evaluate costs. Lens surgery, a equently performed operation in the hospital, is used as an example to evaluate criteria of adequate service and efficiency. This method is based upon L.J. Caronito s bifocal model of clinical nursing.     

Image formation by the crystalline lens and eye of the rainbow trout

The image of a distant unresolved point (point image or PI) and modulation transfer function (MTF) of the eye and lens of the trout were recorded with high spatial (0.3 micron) and dynamic (4096 grey levels) resolution for various entrance aperture sizes and focal positions in monochromatic light, and in broadband light simulating sunlight absorbed by a retinal cone pigment. The PI is irregular, with streaks, wisps and speckle, as a result of lens structural irregularity and diffraction of light scattered within the lens and cornea. Maximum diameter of a diffraction-limited aperture area of the eye is about 0.3 mm. Axially spaced multiple foci are caused by irregular and discontinuous zonal spherical aberration. Lens substance dispersion causes strong longitudinal chromatic aberration, resulting in a broadband PI with concentric coloured haloes. Incident linearly polarized light is slightly depolarized in the PI. The nature of the image is discussed relative to lens and cornea structure, optical modelling and vision. Human subjective entoptic phenomena analogous to those observed objectively in the trout are described.     

Glutathione levels of the human crystalline lens in aging and its antioxidant effect against the oxidation of lens proteins

This paper reports the role of glutathione (GSH) in the crystalline lens as an antioxidant against the oxidation of lens protein. GSH levels in normal lenses decreased gradually with increasing age, from approximately 5 mumol per g lens (wet weight) to 3 mumol per g lens (wet weight). On the other hand, levels of oxidized GSH in the lenses increased until the age of 40. After that, it remained almost constant at the level of approximately 0.9 mumol per g lens. Protein-bound GSH levels in both soluble and insoluble lens proteins dropped noticeably in the 50-year and older age groups, although there were significant differences in levels between both fractions. A decrease of tryptophan and tyrosine residues in lens proteins was proportional to a decrease in GSH levels in the lens as a result of aging. Those residue levels in the cataractous lenses were approximately half those in the normal lens proteins, and GSH levels in such lenses were almost one-tenth that in the normal lens. This study revealed that GSH may play an important role in preventing the oxidation of lens proteins from various oxidants. Furthermore, it is conceivable that these normal changes in GSH levels in the lenses increase the vulnerability of the lens to senile cataractogenesis.     

Ocular chrysiasis correlated with gold concentrations in the crystalline lens during chrysotherapy

The eyes of 11 patients with rheumatoid arthritis (RA) who received extended chrysotherapy (mean cumulative dose greater than 7 grams during a mean 6-year period) were examined biomicroscopically. Minute reddish-purple particles were seen in the cornea (corneal chrysiasis) in 5 and in the lens (lens chrysiasis) in 4 patients. Particulate deposits were absent in 11 other RA patients who had not received gold treatment. Seven crystalline lenses from 5 gold-treated patients were removed surgically because of incidental cataract formation and analyzed for gold content using neutron activation analysis. Although the mean lens gold concentration was higher in these patients than in non-gold-treated controls without RA (0.0073 microgram/grams versus 0.001 microgram/grams), the absolute gold level was markedly lower than that found in 25 diverse tissue analyzed previously. This finding is compatible with the absence of clinical gold-related lens disease or visual impairment.     

Ocular characteristics associated with rigid gas-permeable lens adherence

PURPOSE: Rigid gas-permeable (RGP) lens adherence after overnight lens wear is clearly a patient-dependent phenomenon. However, no previous study has attempted to determine whether specific ocular characteristics are associated with an increased frequency of lens adherence. METHOD: In this study, clinically applicable tests were used to measure a range of ocular characteristics, including central and peripheral corneal curvature, tear film status, eyelid characteristics, central corneal thickness, and ocular rigidity in a group of 22 young adult subjects for whom reliable estimates for frequency of overnight RGP lens adherence had been obtained from earlier studies. RESULTS: Linear discriminant analysis revealed that a higher frequency of lens adherence was associated with lower ocular rigidity, thinner central corneas, greater eyelid tension, and lower amounts of corneal astigmatism. CONCLUSIONS: These findings suggest a clinical approach for identifying patients who may develop clinically significant lens adherence during RGP extended wear, and also provide support for the "thin film adherence" theory of RGP lens adherence.     

The effect of phenazine methosulphate on intermediary pathways of glucose metabolism in the lens at different glycaemic levels

In this study changes in alternative pathways of glucose metabolism are examined in the rat lens using radiolabelled glucose in a 1 hr in vitro incubation of 50 mM or 10 mM glucose with or without 0.1 mM phenazine methosulphate (PMS). PMS which reoxidizes NADPH ensures that the pentose phosphate pathway (PPP) is not limited by the supply of NADP+. The data shows that maximal activation of the PPP (with PMS) is 40% greater at high glucose concentrations than normal glucose. This difference in maximal stimulation may be explained by the increase glucose uptake in the hyperglycaemic incubation. In the high-glucose incubation with PMS, hexokinase activity and the glucose 6-phosphate pool is not limiting for the PPP. Under these conditions, PMS alter the NAD+/NADH and NADP+/NADPH ratio. The change in the redox state alters the flux through the polyol pathway, the glycerol 3-phosphate shuttle and the glycolytic control sites, glyceraldehyde 3-phosphate, pyruvate and lactate dehydrogenases. These results are discussed in relation to hyperglycaemia-induced oxidative stress.     

Creep characteristics of single crystalline Ni3Al(Ta,B)

The creep characteristics, including the nature of the creep transient after a stress reduction and activation energy for creep of single crystalline Ni₃Al(Ta,B) in the temperature range 1083 to 1388 K, were investigated. An inverse type of creep transient is exhibited during stress reduction tests in the creep regime where the stress exponent is equal to 3.2. The activation energy for creep in this regime is equal to 340 kJ mol⁻¹. A normal type of creep transient is observed during stress reduction tests in the regime where the stress exponent is equal to 4.3. The activation energy for creep in this regime is equal to 530 kJ mol⁻¹. The different transient creep behavior and activation energies for creep observed in this investigation are consistent with the previous suggestion that then = 4.3 regime is associated with creep controlled by dislocation climb, whereas then = 3.2 regime is associated with a viscous dislocation glide process for Ni₃Al at high temperatures.     

Accommodation and presbyopia in the human eye. Changes in the anterior segment and crystalline lens with focus

PURPOSE: To characterize changes in the sagittal dimensions of the human crystalline lens and anterior segment as a function of accommodation, to determine the potential age dependence of these changes, and to evaluate these changes in relation to the development of presbyopia. METHODS: Scheimpflug slit-lamp photography, as well as a variety of standard ophthalmologic methods, was used to collect information about lens and anterior segment sagital dimensions in a population of 82 adults with refractive error < or = magnitude of 2.0 diopters and at least 0.25 diopter of accommodation for subjects 18 to 70 years of age. Data were analyzed statistically for dependence on accommodation, age, and age dependence of accommodative rate. RESULTS: The rate of change per diopter of accommodation for each measured variable within the lens is independent of age for the entire adult age range. With increasing accommodation, the lens becomes thicker and the anterior chamber shallower along the polar axis. This increase in sagittal lens thickness is entirely because of an increase in the thickness of the lens nucleus. Because the anterior and posterior halves of the nucleus increase in thickness at approximately the same rate with accommodation, the increase in lens thickness results from equal changes in the lengths of the anterior and posterior portions. CONCLUSIONS: Because changes along the sagittal axis of the anterior segment with accommodation are independent of age, any explanation of presbyopia that relies on simple changes in the rates of lens thickening and anterior chamber shallowing with age does not hold. In light of other age-related changes in the anterior segment and lens (e.g., increased sharpness of lens curvature, increased lens sagittal thickness, decreased anterior chamber depth), it appears that compensatory mechanisms to preserve far vision with age also preserve the rate of change per diopter of sagittal spacings.     

Cell sources, regulatory factors and gene expression in the regeneration of the crystalline lens and retina in vertebrate animals

Over the past century extensive experimental materials have been accumulated concerning cell sources of lens and retina regeneration, successive transformations of the cells, regulatory factors, and gene expression during restitution of these eye structures. The use of nuclear and cytoplasmic markers provided convincing evidence that the removed lens is restituted from the dorsal iris cells in vivo or from embryonic cells of the pigment epithelium and retina in vitro. The removed or destroyed retina is restituted as a result of transdifferentiation of the pigment epithelium cells in amphibians, fish, birds, and mammals during embryogenesis, in larvae of some anuran amphibians, and in adult newts. Cell precursors of rods are a cell source of retina regeneration in adult fish. A subpopulation of randomly distributed cells, which are a cell source of rod formation during the normal development of the eye was found in the external nuclear layer with the use of electron microscopy and nuclear and cytoplasmic markers. These cells are not only a source of regeneration of rods, but also of cones and cells of the internal nuclear layer after destruction of the corresponding retina layers. There is a peripheral growth area in the retina of vertebrates, where multi- and unipolar cells are localized, which provide for the retina growth during ontogenesis. A paradox of retina regeneration consists in that these little differentiated cells are not a source of complete restitution of the removed or destroyed retina. They make only a small contribution to its regeneration corresponding to the growth potential of cells of this eye region, while restitution of the retina proceeds only at the expense of cells of another type of differentiation. A factor controlling the differentiated state of the cell was found in the dorsal iris during studies of lens regeneration. Removal of this factor in the early stages of cell transformations leads to the initiation of lens regeneration. The factor is not specific and was identified in many cells of vertebrates, including the pigment epithelium and limb tissues, which, as is known, may be fully restituted. Studies of gene expression during lens and retina regeneration are now at the initial stage. The greatest advances were achieved on the model of transdifferentiation of the pigment epithelium cells of chick embryos into lentoids. Expression of genes MMP115 and pP344 was established in the pigment epithelium cells, which characterize the pigmented phenotype of the initial cells. Expression of the alpha-, beta-, and delta-crystallin genes was found in the lentoids, which characterize the phenotype of regenerating structures. The gene activity appears to be switched at an intermediate stage during cell dedifferentiation. Expression of the gamma-crystallin genes during lens regeneration in adult newts is initiated after completion of dedifferentiation and cell proliferation in the dorsal iris. The genes specifically expressed in the dorsal and ventral iris and in the retina rudiment have been identified by the method of gene subtraction. Expression of homeobox-containing genes from the family of PAX genes was found during lens regeneration in adult newts and retina regeneration in adult fish. The role of growth factors (FGF) as morphogenetic factors was proved, which are involved in a yet unknown way of altering the differentiation pathway of the initial cells during formation of the neuroepithelium rudiment in chick embryos, adult newts, and fish.     

The effect of tonicity on lens volume

Rat lenses incubated in hypotonic medium adapted to the medium by first undergoing osmotic swelling and then returning after 1 to 2 days to their originial volume. Two processes--osmotic swelling and volume regulation--appear to be working simultaneously. The former is indicated by a decrease in the concentration of cell potassium to the expected level and the latter by a limitation of lens volume associated with a decrease in the potassium content of the lens. These findings are consistent with those observed in other types of cells and may be of significance in understanding the etiology of cataracts.     

The conjunctiva in senile lens exfoliation

Conjunctival biopsy specimens from both eyes of a series of seven patients with evidence of unilateral senile exfoliation of the lens were examined by electron microscopy. Exfoliation fibers were found in both eyes of each patient. This evidence suggests that the conjunctiva is an independent source of exfoliation that precedes the development of exfoliation in the lens.