[Alternative methods of surgical treatment of keratoconus]. / Al'ternativnye metody khirurgicheskogo lecheniya keratokonusa.

The introduction of early diagnostic methods for keratoconus into clinical practice has become the basis for the development of surgical treatment techniques for this pathology, such as corneal collagen crosslinking and interlamellar keratoplasty with implantation of intrastromal segments. The article analyzes the results of research by Russian and foreign specialists in these areas and presents the data on the combination of SMILE surgery and corneal crosslinking, the Rome protocol of corneal crosslinking, modifications of interlamellar keratoplasty, the use of femtosecond laser technologies, and some pilot studies. Modern requirements for ophthalmological care require a personalized approach to each patient, and therefore the surgeon should have a wide range of surgical methods of treatment applicable to different patient cohorts. The described methods of treatment, according to the authors, are the most promising.

From decimeter-scale elevated ionic conductivity regions in the cloud to lightning initiation.

In this work, we represent the lightning initiation scenario as a sequence of two transitions of discharge activity to progressively larger spatial scales: the first one is from small-scale avalanches to intermediate-scale streamers; and the second one is from streamers to the lightning seed. We postulate the existence of ion production centers in the cloud, whose occurrence is caused by electric field bursts accompanying hydrometeor collisions (or near collisions) in the turbulent thundercloud environment. When a new ion production center is created inside (fully or partially) the residual ion spot left behind by a previously established center, there is a cumulative effect in the increasing of ion concentration. As a result, the essentially non-conducting thundercloud becomes seeded by elevated ion-conductivity regions (EICRs) with spatial extent of 0.1-1 m and a lifetime of 1-10 s. The electric field on the surface of an EICR (due to its conductivity being at least 4 orders of magnitude higher than ambient) is a factor of 3 or more higher than ambient. For a maximum ambient electric field of 100 kV/m typically measured in thunderclouds, such field enhancement is sufficient for initiation of positive streamers and their propagation over distances of the order of decimeters, and this will be happening naturally, without any external agents (e.g., superenergetic cosmic ray particles) or extraordinary in-cloud conditions, such as very high potential differences or very large hydrometeors. Provided that each EICR generates at least one streamer during its lifetime, the streamers will form a 3D network, some parts of which will contain hot channel segments created via the cumulative heating and/or thermal-ionizational instability. These hot channel segments will polarize, interact with each other, and cluster, forming longer conducting structures in the cloud. When the ambient potential difference bridged by such a conducting structure exceeds 3 MV, we assume that the lightning seed, capable of self-sustained bidirectional extension, is formed.

Stepwise injection potentiometric determination of caffeine in saliva using single-drop microextraction combined with solvent exchange.

A flow potentiometric method for determination of caffeine in saliva is suggested. This task is important for non-invasive assessment of drug metabolizing system activity in hepatocytes. In the current study, stepwise injection analysis (SWIA) was successfully combined with single-drop liquid microextraction (SDLME) and solvent exchange procedure. The method is based on the caffeine SDLME with subsequent solvent evaporation and dissolution of analyte in sulfuric acid followed by potentiometric detection using poly(vinyl chloride) membrane electrode containing potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as electroactive component. SDLME was employed for elimination of interfering matrix effects of saliva and caffeine metabolites such as theophylline, theobromine and paraxanthine. A linear range of 10(-5)-10(-2)M was established for caffeine with detection limit at 6 × 10(-6)M. The sample throughput was 6 samples h(-1). The proposed method was successfully applied to the determination of caffeine in saliva and the analytical results agreed well with the results obtained with reference HPLC method.

Effects of distractors on the perception of right angles.

Psychophysiological experiments were performed in which imaginary right angles formed by three spots of light were supplemented by distracting line segments. The subjects' task was to restore the orthogonality disturbed by the distractors. Subjects' errors were assessed in relation to the distance between the basal spots and the distractors. The results led to the suggestion that there are specific lateral interaction processes involving local averaging of information on the positions of stimulus components. Quantitative evaluation of the parameters of this interaction was addressed using a simplified mathematical model constructed on the basis of the concept of displacements of the centers of gravity resulting from summation of the corresponding excitation patterns in the neural networks of the visual system. Good consistency between theoretical and experimental data was obtained.

[Stimulus size and visual illusion of extent].

In psychophysical experiments, the dependence of magnitude of the illusion of extent on the length of the referential part of a modified Brentano figure with different size of the imaginary wings was studied. The experimental data obtained were interpreted in terms of a model based on the concept ofcentroid biases of excitatory patterns, evoked by stimulus terminators. A good resemblance between the expetimental and computational data confirms the modeling assumption on increase of the area of perceptual influence in dependence on the eccentricity in the visual field. The estimated model parameters support a suggestion that distortions of perceived position of the centers-of-masses of stimulus terminators may be considered as one of the main reasons of the illusion of extent. The model parameters also have showed favor to a possible link of the phenomenon of the illusion investigated with perception of three-dimensional coordinates of visual objects.

[Distracter effect on the right angle perception].

On the monitor three light spots form imaginary sides of the right angle. The perceived angle distortions arose when distracting stripes were flanking each stimulus spot and subjects were asked to readjust the orthogonal orientation of the sides. The dependence of the subject's error value on the spot-to-stripe distance was measured. The data obtained was referred to a certain lateral interaction processes which manifested themselves as a local information averaging concerned with the positions of the stimulus parts. The quantitative parameters of the lateral interaction were established by a simplified mathematical model based on the conception of the centroid biases which are due to summation of the corresponding patterns of excitations in the visual pathways. A good agreement between the computational and experimental data was obtained.

Dynamics of spatial resolution of single units in the lateral geniculate nucleus of cat during brief visual stimulation.

Sharpness of vision depends on the resolution of details conveyed by individual neurons in the visual pathway. In the dorsal lateral geniculate nucleus (LGN), the neurons have receptive fields with center-surround organization, and spatial resolution may be measured as the inverse of center size. We studied dynamics of receptive field center size of single LGN neurons during the response to briefly (400-500 ms) presented static light or dark spots. Center size was estimated from a series of spatial summation curves made for successive 5-ms intervals during the stimulation period. The center was wide at the start of the response, but shrank rapidly over 50-100 ms after stimulus onset, whereupon it widened slightly. Thereby, the spatial resolution changed from coarse-to-fine with average peak resolution occurring approximately 70 ms after stimulus onset. The changes in spatial resolution did not follow changes of firing rate; peak firing appeared earlier than the maximal spatial resolution. We suggest that the response initially conveys a strong but spatially coarse message that might have a detection and tune-in function, followed by transient transmission of spatially precise information about the stimulus. Experiments with spots presented inside the maximum but outside the minimum center width suggested a dynamic reduction in number of responding neurons during the stimulation; from many responding neurons initially when the field centers are large to fewer responding neurons as the centers shrink. Thereby, there is a change from coarse-to-fine also in the recruitment of responding neurons during brief static stimulation.

Distortions in length perception: visual field anisotropy and geometrical illusions.

Psychometric experiments were performed to study the effects of visual field anisotropy and geometrical illusions on the accuracy of comparison of objects in terms of length. Stimuli consisting of V-shaped symbols were used, made up of three light spots or one spot plus components of illusory figures, which were pairs of Müller-Layer wings or an interval of the Oppel-Kundt figure filled with spots of light. Relationships between the length comparison errors and the orientations of the reference and test parts of the stimulus were obtained. The experimental data showed that the simultaneous appearance of illusions and visual field anisotropy can be summed algebraically.

[Effect of striate visual cortex topography on the parameters of image filtering]. / Vliianie topografii pervichnoi zritel'noi kory na parametry fil'tratsii izobrazheniia.

A model of spatial-frequency filtering at the level of 4C layer of the striate visual cortex is proposed and based on the well-known literature data. The evidence on conformable character of representation of the visual field on the primary visual cortex and the suggestions concerning uniformity of horizontal connections of cortical neurones serve as the ground of the model. A correspondence between predictions of the model and results of the experiments with shape perception and size discrimination has been obtained.

[Distortions of length perception: anisotropy of the visual field and geometric illusions]. / Iskazheniia vospriiatiia dliny: anizotropiia zritel'nogo polia i geometricheskie illiuzii.

A combined influence of stimulus orientation and structure on the judgement of length was tested in psychophysical experiments. The subjects adjusted the test part of a stimulus to be equal in length to the reference part. The V-shaped stimuli (three dots, or the Oppel-Kundt figure, or one dot and two Müller-Layer wings) were generated on the monitor. In the Oppel-Kundt and Müller-Layer figures, the filled part was considered as a reference and the empty part as a test. In session of the experiments, values of errors measured as functions of orientation of the parts of the stimuli. We assume that experiments with the three-dot stimuli yielded pure characteristics of visual field anisotropy, while those with the Oppel-Kundt and Müller-Layer figures showed a combined effect of both anisotropy and illusions. The data demonstrated that illusions and anisotropy are to be interpreted as independent factors, which converge to an algebraic summation in a simultaneous manifestation.

Phase mixing, induced relaxation, and chaos in one-dimensional dynamical systems.

This paper investigates the mechanism of induced phase mixing, which leads to effective dissipation in classical nonlinear dynamical systems with a fast modulation of the potential. The suggested model can be applied to a classical dynamical description of cold atomic clouds in optical traps. We show that the parametric nonadiabatic modulation of the laser intensity can provide a tool for dynamical control of the effective relaxation in such systems.

Distortions of length perception.

A combined influence of stimulus orientation and structure on the judgment of length was tested in psychophysiological experiments. The subjects adjusted the test part of a stimulus to be equal in length to the reference part. The orientation of the parts of the stimulus varied in the experiments. The stimuli (three dots or the Oppel-Kundt figure, which had ten dots within the filled part) were generated on the monitor. In the Oppel-Kundt figure, the filled part was considered as a reference and the empty part as a test. In sessions of the experiments, values of errors were measured as functions of the size and orientation of the stimulus. The reference part length varied within 14-150 min are range, and the orientation was fixed in 0 degree, 90 degrees, 180 degrees or 270 degrees positions. The orientation of the test part varied from 0 degree to 360 degrees in 7 degrees steps. We assume, that the experiments with the three-dot stimuli yielded pure characteristics of visual field anisotropy, while those with the Oppel-Kundt figure showed the combined effect of both the components (anisotropy and spatial filtering). The data demonstrated independence of the two factors from each other in a simultaneous manifestation. The characteristics of a pure Oppel-Kundt illusion have been found to be in close correspondence with the predictions of the model of spatial filtering.

Compound heterozygous deletion of the PROP-1 gene in children with combined pituitary hormone deficiency.

Mutations in the prophet of Pit-1 gene (PROP1) have been shown to be responsible for combined pituitary hormone deficiency (CPHD) with deficiencies of growth hormone (GH), Prolactin (Prl), thyroid-stimulating hormone (TSH) and gonadotropins. We previously reported that homozygosity for a 2bp deletion in exon 2 (296delGA) accounted for CPHD in three patients from two Russian families. Here we report a second mutational hot spot in exon 2. This 2bp 149delGA deletion results in a frame shift that leads to the same serine to stop codon change at codon 109 (S109X). The predicted proteins are each truncated at residue 108 but diverge from the wild type sequence at different points in the homeodomain. Compound heterozygosity for the two mutations (149delGA/296delGA) was detected in 5 of 14 CPHD children from 4 families (36%). This provides the first evidence of heterozygosity for two common deletions as a cause of CPHD in Russian children.

A mutational hot spot in the Prop-1 gene in Russian children with combined pituitary hormone deficiency.

Combined pituitary hormone deficiency (CPHD), including growth hormone (GH), prolactin (Prl) and thyroid-stimulating hormone (TSH) in children is now considered a heterogeneous syndrome. Recent findings on expression of mouse pituitary-specific homeodomain factors demonstrate dependence of adenopituitary ontogeny on interactive expression of these factors, suggesting their involvement in etiology of CPHD. Prophet of Pit-1 (Prop-1) gene, a novel pituitary-specific homeodomain factor, was analyzed in 14 Russian children with CPHD, in whom Pit-1 gene was intact. We found a mutational hot spot in three patients from two families in homeodomain part of the second exon of Prop-1 gene. The common 2-base pair deletion (GA296) in the homozygous state resulted in a Serine to Stop codon (S109X) substitution and generated a truncated Prop-1 protein. Parents were phenotypically normal and heterozygous for GA296 deletion, indicating an autosomal recessive inheritance. These results demonstrate a novel type of Prop-1 gene mutation as one of the causes of CPHD in Russian patients.

Two-dimensional inverse problem of diffusion tomography: the approach applicable for small inclusions.

A method for solving the two-dimensional inverse problems of optical diffusion tomography is proposed. The method is especially designed for the imaging of small inclusions embedded in the backgrounds of strongly scattering media. Numerical simulations show that the results are stable with respect to external noise at the boundary of the sample. The location of an inclusion is obtained with an accuracy of the order of several photon transport mean-free paths in the medium in cases both with and without noise in the scattering data used for the solution of the inverse problem.

Biochemical nature of high-molecular-weight prolactin of human serum: identification of a prolactin-binding protein.

The biochemical nature of a high-molecular-weight immunoreactive prolactin (HMW-irPRL) prepared by gel filtration of women's sera with predominance of this hormone form was studied. Immunochemical characteristics of HMW-irPRL are different from those of 23 kD prolactin (23 kD-PRL). A protein which specifically and reversibly binds to human [125I]PRL is isolated from the pooled fractions of HMW-irPRL by affinity chromatography on prolactin-Sepharose. According to gel filtration, the binding protein (BP) has molecular weight about 150 kD, and it reversibly binds to protein A immobilized on Sepharose. Analysis of BP by SDS-PAGE resulted in two major protein bands, of 65-70 and approximately 150 kD. Both the bands, when transferred to nitrocellulose, interacted with [125I]protein A. Binding of highly purified human pituitary prolactin to the BP significantly decreased the immunoreactivity of the hormone. The molecular weight of BP and its interaction with protein A and recognition by poly- and monoclonal antibodies against human (but not guinea pig) IgG indicate that BP may be an immunoglobulin. Thus, our data demonstrate that HMW-irPRL is formed by the binding of 23 kD-PRL to a specific serum protein which is probably an anti-prolactin IgG.