This work was supported by a grant from the Bonneville Power Administration. A.D.R. was supported by a National Research Council Postdoctoral Fellowship.
Well-defined fronts develop at the seaward ...edge of riverine plumes where suspended materials and planktonic organisms are concentrated by convergent water flows. Riverine plume fronts have been hypothesized to be favorable fish habitats because they can lead to localized preyaggregations. We examined the spatial distribution of juvenile Pacific salmonids Oncorhynchus spp. in and around plankton-rich frontal regions of the Columbia River plume to test the hypothesis that juvenile salmonids aggregate at riverine plume fronts to feed. Juvenile salmonids tended to be abundant in the frontal and plume regions compared to the more marine shelf waters, but this pattern differed among species and was not consistent across the 2 study years. Stomach fullness tended to be higher in the more marine shelf waters than either the front or plume areas, which does not support the hypothesis that salmonids consistently ingest more prey at frontal regions. Many prey organisms were disproportionately abundant at these fronts, but salmon stomach-content analysis did not reveal higher stomach contents at fronts or identify prey groups indicative of feeding in the frontal areas. Although our results indicate that the Columbia River plume influences the distributions of juvenile salmon, our observations do not support the hypothesis that juvenile salmonids congregate to feed at fronts at the leading edge of the Columbia River plume. The short persistence time of these fronts may prevent juvenile salmon from exploiting these food-rich, but ephemeral, features.
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Use of fish-specific toxic equivalency factors (TEFs) to estimate the risk that exposure to polybrominated dibenzo-p-dioxins (PBDDs), dibenzofurans (PBDFs), and biphenyls (PBBs) pose to fish early ...life stage survival depends on validation of the hypothesis that these chemicals act additively to produce mortality. A rainbow trout early life stage bioassay was used to determine how pairs of PBDD, PBDF, and PBB congeners interact to produce 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like toxicity associated with sac fry mortality. The congener pairs tested were 2,3,7,8-tetra- bromodibenzo-p-dioxin (2,3,7,8-TBDD)/1,2,3,7,8-pentabromodi- benzop-dioxin (1,2,3,7,8-PBDD); 2,3,7,8-TBDD/1,2,3,7,8-penta- bromodibenzofuran (1,2,3,7,8-PBDF); 1,2,3,7,8-PBDD/2,3,4,7,8-pentabromodibenzofuran (2,3,4,7,8-PBDF); and 2,3,4,7,8-PBDF/3,3′,4,4′-tetrabromobiphenyl (3,3′,4,4′-TBB). Graded doses of each congener alone, or graded doses of fixed ratios of paired congeners were injected into newly fertilized rainbow trout eggs. In all cases, interactions between congener pairs were additive as tested by a probit model. Isobolographic analysis also supported the hypothesis that the PBDD, PBDF, and PBB congeners act additively. Thus, the use of fish-specific TEFs to convert fish tissue concentrations of individual PBDD, PBDF, and PBB congeners to TCDD equivalents (TEs) and then adding the TEs contributed by the various congeners to give the total TCDD equivalents concentration (TEC) in the tissue is supported by these results. By comparing the TEC in feral fish eggs to the fish egg TCDD no-observed-effect level (NOEL) and lowest-observed-effect level (LOEL) for early life stage mortality, the risk that complex mixtures of these polybrominated chemicals in eggs pose to sac fry survival can be estimated.
Multifocal intraocular lenses Duffey, R J; Zabel, R W; Lindstrom, R L
Journal of cataract and refractive surgery,
07/1990, Letnik:
16, Številka:
4
Journal Article
Recenzirano
Current multifocal intraocular lens designs incorporate refractive or diffractive optical principles to achieve increased depth of focus. Information about four basic design concepts is presented. ...Early clinical results with two of these, the IOLAB Nuvue two-zone refractive multifocal and the 3M diffractive multifocal, are summarized.
Fish in many areas are contaminated with 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) and related polychlorinated dibenzo‐p‐dioxin (PCDD), dibenzofuran (PCDF), and biphenyl (PCB) congeners. Other ...chemicals may also be present that act through the same mechanism. 2,3,6,7‐Tetrachloroxanthene (TCX) has been found to be an interference in PCDD and PCDF analyses and may occur in sediments near pulp and paper mills. However, the toxicology of TCX has not been studied in any species. This study sought to determine whether TCX causes TCDD‐like effects in two fish systems, rainbow trout early life stages and rainbow trout gonadal cells (RTG‐2) in culture. 2,3,6,7‐Tetrachloroxanthene caused rainbow trout sac fry mortality secondary to blue sac syndrome, identical to that caused by TCDD, and was similar in potency to TCDD for causing cytochrome P4501A mRNA induction in RTG‐2 cells and sac fry mortality in rainbow trout, with toxic equivalency factors of 1.09 to 2.29. These results suggest that TCX may pose a risk to feral fish in contaminated areas even at low concentrations.
Phototherapeutic keratectomy using a 193-nm excimer laser was performed at four centers on 33 sighted patients with corneal opacity and/or irregular astigmatism. Pathologic conditions included ...anterior stromal and superficial scarring from postinfectious and posttraumatic causes, including inactive herpes simplex virus, anterior corneal dystrophies, recurrent erosions, granular dystrophy, and band keratopathy. Most patients received peribulbar anesthesia and underwent removal of the epithelium prior to laser ablation. A majority of patients had a reduction in the amount of corneal scarring and approximately half had improved visual acuity. No intraocular reaction or changes in endothelial counts were seen, and some patients avoided the need for penetrating keratoplasty. Reepithelialization usually occurred within 4 or 5 days and we noted no significant scarring secondary to use of the laser. It was difficult to eliminate preexisting irregular astigmatism despite the use of surface modulators, such as methylcellulose. A hyperopic shift secondary to corneal flattening was encountered in approximately 50% of the patients. A combination of myopic ablation, followed immediately by a secondary hyperopic steepening, may minimize this refractive change. The 193-nm excimer laser is an effective new tool in the treatment of selected patients with superficial corneal opacity from a variety of conditions.
Use of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity equivalents concentration (TEC) assumes that polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) act ...additively and via a common mechanism to cause toxicity. To test these assumptions, 11 TCDD-like congeners and three non-TCDD-like congeners were combined at ratios typically found in Lake Michigan lake trout. The potency of the mixture, expressed as TEC based on fish-specific toxic equivalency factors, was compared to TCDD for producing lake trout and rainbow trout early life stage mortality. Signs of toxicity following exposure of newly fertilized eggs to the mixture or to TCDD were indistinguishable; sac fry mortality associated with blue-sac disease, and slopes of the dose–response curves for percentage sac fry mortality versus egg TEC or versus egg TCDD were parallel. However, the mixture dose–response curves were significantly shifted to the right of the TCDD dose–response curves by 1.3- to 1.8-fold as illustrated by LD50values. Following exposure to the mixture or TCDD, LD50s for lake trout early life stage mortality were 97 (89–110) pg TE/g egg and 74 (70–80) pg TCDD/g (LD50, 95% fiducial limits) and for rainbow trout were 362 (312–406) pg TE/g egg and 200 (148–237) pg TCDD/g egg. These data suggest that TCDD-like congeners act via a common mechanism to cause toxicity during trout early development, but may not act strictly additively when combined in a mixture of TCDD- and non-TCDD-like congeners at ratios found in Great Lakes fish. The deviation from additivity, however, is less than current safety factors of 10-fold commonly applied in ecological risk assessments, providing support for the continued use of a TE additivity model for assessing risk posed by complex mixtures of PCDDs, PCDFs, and PCBs to fish.
Multifocal intraocular lenses are intended to increase depth of focus for patients with cataracts, but optical considerations predict reduced retinal-image contrast. We evaluated visual performance ...through multifocal intraocular lenses by measuring contrast sensitivity functions and reading speed for age-matched groups with multifocal and monofocal intraocular lenses and two normal control groups. Contrast sensitivity functions of the patients with multifocal lenses did not differ significantly for optical distances differing by 2.5 diopters, indicating substantial depth of focus. Normal and monofocal contrast sensitivity functions were nearly identical, and both were about a factor of two higher than multifocal contrast sensitivity functions. Patients with multifocal lenses showed deficits in reading speed only for low-contrast text (less than 30%) and small letters (0.2 degree and 1.0 degree).
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