Is the maximum hypermetropic correction necessary in children with fully accommodative esotropia?

AIMS: This prospective study explores the effect of reduction in hypermetropic refractive correction on the angle and control of fully accommodative esotropia. METHODS: 30 childhood cases with fully accommodative esotropia were recruited. The angle of deviation with and without full hypermetropic correction (near and distance) was measured. The overall effect of reduction of the correction by one and two spherical dioptres (DS) on the angle and control of the deviation was identified. RESULTS: With the full hypermetropic correction in place, the angle of deviation for near was less than 10 prism dioptres (pd) in 73% of the participants, and the distance deviation was less than 10 pd in 93%. When the prescription was reduced by 1.00 DS, the percentage of those with a near deviation of less than 10 pd fell to 30% and 57% for the distance. Twenty per cent immediately decompensated to manifest esotropia with reduction of 1 dioptre of spectacle correction. CONCLUSION: Children with fully accommodative esotropia who are given the full hypermetropic correction demonstrate smaller, more controllable angles of deviation than those who are undercorrected by as little as only one dioptre. This supports the practice of providing the maximum hypermetropic correction for childhood esotropes.

Electrochemical sensor for measurement of urea and creatinine in serum based on ac impedance measurement of enzyme-catalyzed polymer transformation.

Enzyme-catalyzed polymer transformation with electrochemical ac impedance detection has been employed for the measurement of urea and creatinine in serum samples. A polymer, based on poly(methylvinyl ether)/maleic anhydride modified by esterification with n-octanol, which is stable at pH 7.4 and which is transformed rapidly in response to alkaline pH changes, was linked to enzymatic reactions between urease and urea or creatinine deiminase and creatinine to produce a disposable sensor system. The polymer was screen-printed onto interdigitated screen-printed carbon electrodes and the electrodes overlaid with absorbent pads containing the relevant enzyme. Application of serum samples, "spiked" with either urea or creatinine, resulted in rapid polymer transformation, and resultant changes in the capacitance of the polymer-coated electrodes were analyte-concentration dependent. Additional information on the mechanisms of polymer transformation was obtained from dynamic quartz crystal microbalance measurements.

Specific binding assay for biotin based on enzyme channelling with direct electron transfer electrochemical detection using horseradish peroxidase.

A model 'homogeneous' format enzyme channelling specific binding assay for biotin based on peroxide-sensitive horseradish peroxidase mediatorless enzyme electrodes is described. The procedure involved the immobilisation of avidin onto the surface of printed carbon horseradish peroxidase (HRP) enzyme electrodes and the competitive binding of biotin and biotinylated glucose oxidase. Upon addition of glucose, hydrogen peroxide was generated via the glucose oxidase label. Direct electron transfer between the electrodes and HRP resulted in the detection of H2O2 by electroenzymic reduction at +50 mV vs Ag/AgCl. The cathodic current response could be measured in the presence of excess biotinylated glucose oxidase by incorporation of catalase in homogeneous solution to scavenge H2O2 generated in the bulk before it diffused to the electrode surface. The assay showed greatest sensitivity over the range of biotin concentrations 0.07 to 2 micrograms ml-1 in the presence of 10 micrograms ml-1 excess biotinylated glucose oxidase in the bulk solution.

Amperometric detection of alkaline phosphatase activity at a horseradish peroxidase enzyme electrode based on activated carbon: potential application to electrochemical immunoassay.

Amperometric detection of alkaline phosphatase activity has been achieved using 5-bromo-4-chloro-3-indolyl phosphate (BCIP) as the enzyme substrate. The production of hydrogen peroxide from the dephosphorylation of BCIP was measured using an activated carbon electrode with horseradish peroxidase immobilised to its surface by simple passive adsorption. This method was easily capable of measuring 10(-12) M alkaline phosphatase and had a calculated detection limit of 2.2 x 10(-14) M. The horseradish peroxidase electrode system was investigated further as a method for non-competitive electrochemical enzyme immunoassay using thyrotropin (TSH) as the model analyte. This was realised by co-immobilization to the electrode surface of both horseradish peroxidase and an anti-thyrotropin monoclonal antibody. After addition of the analyte, a second biotinylated anti-thyrotropin monoclonal antibody and the substrate, streptavidin-labelled alkaline phosphatase was added and the current (generated by enzyme channelling of hydrogen peroxide) measured as a function of TSH concentration. Thus, the activated carbon electrode was used as a combined immunological capture phase and amperometric detection system.

Direct electron transfer bioelectronic interfaces: application to clinical analysis.

Bioelectronic interfaces based on direct electron transfer to proteins and enzymes immobilised at functional electrode surfaces are currently under development and the potential of two such systems for application to clinical measurement will be outlined. The first is the detection of free radical production via direct electrochemistry of cytochrome c immobilised covalently at modified gold electrodes. The redox protein cytochrome c has been immobilised covalently to gold electrodes surface-modified with N-acetyl cysteine via carbodiimide condensation. The electrodes thus produced were used to measure directly the enzymatic and cellular production of the superoxide anion radical (O2(-). The superoxide radical reduced the immobilised cytochrome c which was immediately re-oxidised by the surface-modified gold electrode poised at a potential of +25 mV (vs Ag/AgCl). The electron transfer rate constant (ket) of this process was 3.4 +/- 1.2 s(-1). The rate of current generation was directly proportional to the rate of O2(-) production. The essentially reagentless system produced was designed to be applied ultimately to continuous monitoring of free radical activity in vivo since there is evidence that oxygen-derived free radical species act as mediators which cause and perpetuate inflammation in disease states, including rheumatoid arthritis and neurodegenerative disorders. The second systems are pseudo-homogeneous immunoassays based on direct electron transfer to horseradish peroxidase. Horseradish peroxidase enzyme electrodes based on activated carbon (HRP-ACE) have been constructed by simple passive adsorption.(ABSTRACT TRUNCATED AT 250 WORDS)