Disposable contact lens use as a risk factor for microbial keratitis

AIMS: A case-control study was performed to evaluate soft contact lens (SCL) wear modality as a risk factor for microbial keratitis. METHODS: Contact lens wearers presenting as new patients to Moorfields Eye Hospital accident and emergency department during a 12 month period completed a self administered questionnaire detailing demographic data and contact lens use habits. Cases were patients with a clinical diagnosis of SCL related microbial keratitis. Controls were SCL users attending with disorders unrelated to contact lens wear. Odds ratios (estimates of relative risks) and 95% confidence limits (CL) were calculated through multivariable logistic regression analysis. RESULTS: There were 89 cases and 566 controls. A substantially increased risk with 1-4 weekly disposable SCL compared with non-disposable SCL was identified among both daily wear (DW) (odds ratio = 3.51, 95% CL 1.60-7.66, p = 0.002) and extended wear (odds ratio 4.76, 95% CL 1.52-14.87, p = 0.007) users after adjustment for demographic, lens use and hygiene variables. Other significant factors among DW users were "occasional" overnight use, use of chlorine based (as opposed to other chemical) systems in combination with poor storage case hygiene, and irregular disinfection. CONCLUSION: Properties of some disposable SCL may be partly responsible for these excess risks. It is also possible, however, that this finding is largely a reflection of widespread complacency among patients and practitioners with respect to disposable SCL fitting and use.     

Nonselection and nonresponse bias in clinical research

In summary, nonselection and nonresponse bias can have a potent impact on the validity of clinical veterinary research studies and should be carefully assessed by investigators and readers. The risk of nonselection and nonresponse bias has been compared to "lowering yourself into a dark pit and trusting you won't be bitten by a snake ... before you go into the pit, you should stand outside and listen for a hissing sound ... if you hear one, do not go on ... if you do not hear anything, you may proceed with caution, being confident that at worst you will be bitten by a quiet snake."     

Mutations at nonliganding residues Tyr-85 and Glu-83 in the N-lobe of human serum transferrin. Functional second shell effects

The x-ray crystal structure of the N-lobe of human serum transferrin has shown that there is a hydrogen bond network, the so-called "second shell," around the transferrin iron binding site. Tyrosine at position 85 and glutamic acid at position 83 are two nonliganding residues in this network in the human serum transferrin N-lobe (hTF/2N). Mutation of each of these two amino acids has a profound effect on the metal binding properties of hTF/2N. When Tyr-85 is mutated to phenylalanine, iron release from the resulting mutant Y85F is much more facile than from the parent protein. Elimination of the hydrogen bond between Tyr-85 and Lys-296 appears to interfere with the "di-lysine (Lys-206-Lys-296) trigger," which affects the iron binding stability of the protein. Surprisingly, mutation of Glu-83 to alanine leads to the absence of one of the normal iron binding ligands; introduction of a monovalent anion is able to restore the normal first coordination sphere. The missing ligand appears to be His-249, as revealed by comparison of the metal binding behaviors of mutants H249Q and E83A and structural analysis. Glu-83 has a strong H bond linkage with His-249 in apo-hTF/2N, which helps to hold the His-249 in the proper position for iron binding. Disabling Glu-83 by mutation to an alanine seriously disturbs the H bond network, allowing His-249 to move away. A monovalent anion can help reestablish the normal network by providing a negative charge near the position of Glu-83 to reach charge balance, so that ligand His-249 is available again for iron binding.     

Increased endothelin-1 in the rabbit model of middle cerebral artery occlusion

Human neutrophils (5 x 10(4) incubated on fibronectin precoated wells released 2.83 +/- .25 nmoles of superoxide (0(2)-) (x +/- 1 SEM, n = 15) in response to 5.9 nM (100 ng/ml) Tumor Necrosis Factor Alpha (TNF). On the contrary, the 0(2)- production induced by interleukin-8 (IL-8) (doses ranging from 0.1 nM to 1 microM) was comparable to that of "resting" cells (< .6 nmoles/5 x 10(4) cells). IL-8 (100 nM) did not affect the TNF-dependent 0(2)- production when added with TNF at the beginning of the assay, but reduced it by approximately 80% when added with TNF on neutrophils previously incubated for 1 hour on fibronectin. As compared with IL-8, N-formyl-methionyl-leucyl-phenylalanine (FMLP, 100 nM) failed to suppress the TNF-triggering of the oxidative burst in neutrophils plated on fibronectin. The data suggest that the interaction of neutrophils with fibronectin uncovers the capacity of IL-8 to limit the cell response to TNF, without affecting the response to the combination of FMLP and TNF. Thus, although the chemotactic factors IL-8 and FMLP share the capacity of triggering the oxidative burst of neutrophils incubated in suspension, only IL-8 has the potential to down-regulate the responsiveness of fibronectin-adherent cells to TNF.     

Chromosomal assignments of the genes for the calcineurin A alpha (Calna1) and A beta subunits (Calna2) in the rat

PURPOSE: To document the characteristics of the clinical education in internal medicine of undergraduate medical students at Canadian medical schools. METHOD: A five-part questionnaire was sent in 1991-92 to the individuals responsible for supervising the internal medicine clerkships at all 16 Canadian medical schools. The questions were related to (1) tutors, hospitals, and inpatient clinical experiences of internal medicine clerks; (2) ambulatory care experiences; (3) evaluation methods; (4) "junior clerkships" (i.e., clinical courses that precede the clerkships); and (5) supervisors' opinions about changes needed to improve the clerkships. RESULTS: Responses were received from all schools. There was surprising uniformity in clinical education across Canada. Clinical education methods have changed very little over the past decade. In the opinion of the clerkship supervisors, there were too few committed clinical tutors, little evidence of use of newer evaluation methods, and inadequate ambulatory care instruction. CONCLUSION: The study results suggest that the clinical education in internal medicine of undergraduate medical students has changed little despite numerous calls for reform.     

Value of transthoracic echocardiography in predicting embolic events in active infective endocarditis. Duke Endocarditis Service

The purpose of this study was twofold: (1) to determine interobserver variability of echocardiographic characteristics of vegetations in patients with infective endocarditis, and (2) to assess the value of these vegetation characteristics in predicting embolic events. Although echocardiography contributes to the diagnosis of patients with infective endocarditis, its prognostic role in predicting embolic events is controversial. The echocardiograms of 41 patients with infective endocarditis were independently reviewed by 4 echocardiographers blinded to the clinical data. If a vegetation was present, the following characteristics were analyzed: involved site, size, mobility, shape, and pedunculated or sessile attachment. Each echocardiographer also made a "gestalt" estimate of embolic risk based on these vegetation characteristics. Interobserver agreement on vegetation characteristics and their relation to embolic events was then determined using kappa statistics and logistic regression analysis. Interobserver agreement was 98% with regard to echocardiographic vegetation presence and 97% with regard to the involved site. Of the 30 patients in whom vegetations were observed, complete observer agreement was achieved with regard to size in 22 (73%), mobility in 17 (57%), shape in 11 (37%), and attachment in 12 (40%). Vegetations with a maximal diameter of > 10 mm were associated with a 50% incidence of embolic events, compared with a 42% incidence of emboli in patients with vegetations measuring < or = 10 mm. Interobserver variability was great with respect to vegetation shape, mobility, and attachment characteristics. Echocardiographic vegetation characteristics were not helpful in defining the risk of embolic complications in patients with endocarditis.     

Comparative study of 2mol%Li-and Mn-substituted lead-free potassium sodium niobate ceramics

The effect of Li and Mn substitution on the dielectric, ferroelectric and piezoelectric properties of lead free K0.5Na0.5NbO3 （KNN） was investigated. Samples were prepared using a conventional solid state reaction method. The sintefing temperature for all the samples was 1050℃. The optimum doping concentration for the enhancement of different properties without the introduction of any other co-dopants such as Ti, Sb, and La was investigated. X-ray diffraction analysis confirmed that all the samples crystallize in a single phase perovskite structure. The dielectric properties were investigated as a function of temperature and applied electric field frequency. Compared with Li-substituted KNN （KLNN）, Mn-substituted KNN （KMNN） exhibited a higher dielectric constant εmax （i.e., 4840） at its critical transition temperature Tc （i.e., 421℃） along with a lower value of tangent loss at 10 kHz and greater values of saturation polarisation Ps （i.e., 20.14 μC/cm^2） and remnant polarisation Pr （i.e., 15.48 μC/cm^2）. The piezoelectric constant （d33） of KMNN was 178 pC/N, which is comparable to that of lead-based hard ceramics. The results presented herein suggest that B-site or Mn substitution at the optimum concentration results in good enhancement of different properties required for materials used in memory devices and other applications.     

Marginal discrepancy of all-ceramic crowns cemented on implant abutments

PURPOSE: The purpose of this investigation was to determine the mean marginal discrepancy of all-ceramic crowns cemented on implant abutments. MATERIALS AND METHODS: Five Br?nemark CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. The marginal discrepancy was measured using a video camera connected to a digitizing board at four locations on each abutment for five samples in each of the following groups: all-ceramic caps (caps), all-ceramic crowns (crowns), and all-ceramic crowns cemented with zinc phosphate cement (cemented crowns). RESULTS: The mean marginal discrepancies were as follows: caps, 99.0 micrometers (SD, 16); crowns, 117.8 micrometers (SD, 20); and cemented crowns, 168.8 micrometers (SD, 23). Statistically significant differences were found between all three groups at the 99% level of confidence. In addition there were two significant differences between abutments. CONCLUSIONS: Subgingival marginal discrepancies of the magnitude measured in this study have been shown to cause periodontal problems. It is probable that the marginal discrepancy of CeraOne restorations, as tested, can be improved. Efforts should be made to enhance the marginal accuracy of these restorations.     

Peripheral neuropathy: an often-overlooked cause of falls in the elderly

Peripheral neuropathy is common in the elderly and results in impairments in distal proprioception and strength that hinder balance and predispose them to falls. The loss of heel reflexes, decreased vibratory sense that improves proximally, impaired position sense at the great toe, and inability to maintain unipedal stance for 10 seconds in three attempts all suggest functionally significant peripheral neuropathy. Physicians can help their patients with peripheral neuropathy to prevent falls by teaching them and their families about peripheral nerve dysfunction and its effects on balance and by advising patients to substitute vision for the lost somatosensory function, correctly use a cane, wear proper shoes and orthotics, and perform balance and upper extremity strengthening exercises.