Optical method for estimating the equivalent refractive index of the crystalline lens in vivo.

In numerous studies it has been necessary to represent refractive indices of the crystalline lens by an equivalent refractive index (here denoted nL). Its traditional value of 1.416, based on in vitro measurements, may be in error by more than 0.025 in some cases. In vivo estimates are subject to recognized deficiencies of ultrasonography. This study describes and evaluates a new and exclusively optical technique. Using exact ray tracing, nL is found by combining routine optical section data with optical depths that may be measured by a ranging system termed OCDR. Gullstand's no. 1 eye is used to calculate the effects of errors in eye data on the accuracy of the technique. From pooled errors estimated for 22 parameters, a standard deviation of 0.0045 is anticipated for the estimate of nL, although allowance for additional uncertainty associated with the refractive index profile of the lens must await further research.

Relationship between axial length and chromatic refraction of the eye.

A new mathematical expression is derived to provide an estimate, alpha x, of the axial length of the human schematic eye. Approximations in the expression are made after considering effects in the Gullstrand-Emsley schematic eye. Parameters required to solve the expression are, for two wavelengths, the refractive indices of the humours, the focal power of the cornea and refractive errors in two states of accommodation. Unlike recognized optical methods, additional intraocular parameters are not required. For emmetropic variants of the Gullstrand-Emsley schematic eye with axial lengths between 19 and 27 mm, alpha x is within 0.06 to 0.26 mm of the actual value. Furthermore, alpha x is essentially independent of variations in the refractive indices of the crystalline lens. However, the estimate of alpha x is critically dependent on the accuracy of values assigned to the parameters. For that reason, the model is considered impractical for clinical application.

Behavior of animal blood in blood typing systems. Isoelectric focusing of erythrocyte acid phosphatase and phosphoglucomutase.

Isoenzyme band patterns of animal blood erythrocyte acid phosphatase (EAP) and phosphoglucomutase-1 (PGM) were studied by isoelectric focusing on ultrathin polyacrylamide gels. For blood from all animals tested (dog, cat, cow, sheep, and goat), the overall band patterns for both isoenzymes were different from those of the most common human types of these enzymes, although some animal EAP and PGM bands appeared in the human band areas. When mixtures of human and animal red blood cells were studied, it was found that misinterpretation of human types was possible only if the overall band pattern of the mixtures was ignored. For the animal blood tested, the strong PGM bands appearing outside the human band areas could be used as "markers" for the possible presence of animal blood in the samples tested.

Alcohol loss arising from microbial contamination of drivers' blood specimens.

This paper describes the circumstances in which some drivers' blood specimens containing added sodium fluoride (1% w/v concentration) deteriorated as a result of microbial contamination, accompanied by a decrease of alcohol concentration. Strains of the bacteria Serratia marcescens and a Pseudomonas sp. were isolated from the specimens and proven capable of growing at ambient temperature in blood containing sodium fluoride at 1% w/v concentration. They were shown to be active in alcohol degradation in preservatised blood, the activity being dependent on sodium fluoride concentration and storage temperature. Blood diluters were assumed to be a source of microbial cross contamination from one blood specimen to the next. It is recommended that postmortem blood specimens be analysed in separate batches from drivers' specimens when automated blood diluters are used, that the content of fluoride ions be increased to an equivalent of 2% w/v sodium fluoride, and that storage of specimens at temperatures above 4 degrees C be minimised.

Kinetic studies on a glutathione S-transferase from the larvae of Costelytra zealandica.

Of the glutathione S-transferases from the New Zealand grass grub (Costelytra zealandica) active in conjugating the model substrate 1-chloro-2,4-dinitrobenzene, the most active was isolated in a functionally homogeneous form. This had an isoelectric point of 8.7. Preliminary evidence suggests that it is a homodimer with subunits of Mr 23 500. The dependence of the enzyme-catalysed reaction on substrate concentration was analysed in terms of the rate equation characteristic of Ordered Bi Bi or Rapid-Equilibrium Random mechanisms. Evidence was found for a critical ionizing event at pH 9.3 at 37 degrees C. This event appears to involve a twofold change in charge on the enzyme, which may be the result of co-operative ionizations rather than independent ionizations. This appears to affect neither the binding of the aromatic substrate to the enzyme, nor the maximum catalytic velocity of the enzyme-catalysed reaction. The variation of the kinetics with temperature was studied. Apparent thermodynamic parameters characteristic of the reaction were derived. The possible relevance of the temperature-dependence of the enzyme-catalysed reaction in vivo is discussed.

Computer analysis of rapid eye movements.

Simulation of the saccadic eye movement mechanism and, more recently, diagnosis of neuromuscular disorders associated with saccades rely on accurate recording and analysis of saccade characteristics. Traditionally, eye movements are monitored objectively by registering a transduced voltage correlate of eye position on a pen or cathode ray oscillograph. Analysis of the record obtained is tedious and often inaccurate. The advent of small digital computers with analog-to-digital capability permits more efficient recording. However, computer programs reviewed are limited to the analysis of specific saccade parameters or partly depend on manual operations. The computer program described stores the entire saccadic event of each eye between pre-defined limits including the pre- and post-saccade intervals. Preliminary operations including artifact identification, location of onset, elimination of RC decay, DC offset and amplitude scaling prepare the data for display and subsequent analysis. The program also includes a subroutine to derive the mean and standard deviation of successive saccades.