Torsional eye movements in humans

If one has to give a description of eye movements, what first comes to mind is the possibility of the eyes to rotate in horizontal and vertical directions. It is generally less obvious that the eyes are capable of moving in a third. namely the torsional. direction. This capability is by no means hypothetical: humans, as well as other species, possess eye muscles that are pulling in torsional direction and orbital mechanics do allow for a certain amount of torsion. Definition of torsion Torsional eye movements can be defined in two different ways, namely as a rotation about the line of sight and as a rotation about an antero-posterior (forward-to-backward) axis that is fixed in the head

Eye torsion associated with disparity-induced vertical vergence in humans

Recently, Enright described an unexpected association between disparity-induced vertical vergence and cycloversion (conjugate eye torsion) [Enright (1992)Vision Research, 415, 279]. The present experiments were performed to verify these findings and investigate the nature of this association. We presented subjects with a dichoptic image of concentric circles in which a step in vertical disparity of 1 deg was introduced. After 4 sec the disparity was eliminated. Eye movements were measured with scierai coils. We confirmed Enright's findings in that a left-over right vertical vergence was associated with levo-cycloversion (upper poles towards left shoulder) and vice versa. The size of the cycloversion and the vertical vergence were in the same range. In addition we found that part of the cycloversion response was in the form of a torsional nystagmus and that the relative contribution of the left and right eyes was independent of the horizontal gaze angle. These additional findings are in conflict with the hypothesis, offered by Enright, that the association is caused by a bilateral activity of the superior oblique muscles

Dissociated vertical deviation and eye torsion: Relation to disparity-induced vertical vergence

We studied the relation between vertical eye movements and binocular torsion in five subjects with dissociated vertical deviation (DVD). During trials, subject viewed a well illuminated Snellen letter chart, with both eyes uncovered during 4 seconds. Subsequently, DVD was induced by covering one eye during 4 seconds. Finally, both eyes were uncovered during 4 seconds. Several trials were recorded for each subject and covered eye. Eye movements were measured with scleral coils. We found that in all subjects, the vertical divergence followed an exponential course with a time constant of 0.67 ± 0.14 seconds on average. In three of the five subjects this vertical divergence was associated with binocular torsion (cycloversion), partly, in the form of a cycloversional nystagmus. The time course of the vertical divergence as well as the direction and nystagmic nature of the cycloversion was similar to the behaviour that was previously observed in disparity induced vertical vergence in normal subjects. In two of the subjects, the torsion that was associated with the vertical divergence was monocular. Our results indicate that DVD and disparity induced vertical vergence share the same characteristics. In addition, they demonstrate that extorsion associated with the elevation in DVD possibly but not necessarily points at a dissociated torsional deviation

Instability of ocular torsion during fixation: Cyclovergence is more stable than cycloversion

We investigated spontaneous variation of binocular torsion. Variation was expressed as SD of torsional eye positions measured over periods up to 32 sec. Subjects viewed a single dot target for periods of 32 sec. In half of the trials a large random-dot background pattern was superimposed on the dot. The movements of both eyes were measured with scleral induction coils. Spontaneous torsional movements were largely conjugate: cyclovergence was much more stable than cycloversion. This difference was not due to roll head movements. Stability of cyclovergence was improved by the background pattern. Although overall stability (SD of position) of cycloversion was unaffected by a background, the background induced or enhanced a small-amplitude torsional nystagmus in 3 out of 4 subjects. We hypothesize that the difference in stability of cycloversion vs cyclovergence reflects the greater importance of torsional retinal correspondence, compared to absolute torsional position. In two subjects we found evidence for the existence of cyclophoria, manifested by systematic shifts in cyclovergence caused by the appearance and disappearance of the background

Eye torsion elicited by oscillating gratings: Effects of orientation, wavelength and stationary contours

We studied binocular cyclorotatory (torsional) eye movements in response to gratings that oscillated sinusoidally in a frontal plane. The square-wave gratings viewed by the right and left eye were presented and controlled separately to induce cycloversion and cyclovergence by oscillation in phase and out of phase. Eye movements were recorded with scierai induction coils. Stimulus oscillation frequency ranged from 0.125 to 1 Hz and the wavelength of die gratings ranged from 0.92 to 25.75 deg of visual angle. Cycloversion and cyclovergence gain were, on average, comparable in magnitude and decreased with increasing oscillation frequency. There was no consistent effect of the wavelength on the magnitude of the responses. In general, responses were considerably higher to gratings that were oriented horizontally than to those oriented vertically. This anisotropy was present both in cycloversion and cyclovergence. It was enhanced in a larger sized stimulus and by presenting stationary, orthogonal contours (mimicking a “shear” movement), but it was not consistently influenced by wavelength. Cyclovergence showed a phase lag, which increased with oscillation frequency but which was independent of wavelength. In contrast, cycloversion showed a slight phase lead which was independent of bot

Perception of Relative Depth Interval: Systematic Biases in Perceived Depth

Given an estimate of the binocular disparity between a pair of points and an estimate of the viewing distance, or knowledge of eye position, it should be possible to obtain an estimate of their depth separation. Here we show that, when points are arranged in different vertical geometric configurations across two intervals, many observers find this task difficult. Those who can do the task tend to perceive the depth interval in one configuration as very different from depth in the other configuration. We explore two plausible explanations for this effect. The first is the tilt of the empirical vertical horopter: Points perceived along an apparently vertical line correspond to a physical line of points tilted backwards in space. Second, the eyes can rotate in response to a particular stimulus. Without compensation for this rotation, biases in depth perception would result. We measured cyclovergence indirectly, using a standard psychophysical task, while observers viewed our depth configuration. Biases predicted from error due either to cyclovergence or to the tilted vertical horopter were not consistent with the depth configuration results. Our data suggest that, even for the simplest scenes, we do not have ready access to metric depth from binocular disparity.</jats:p

Specific oligomerization of the 5-HT1A receptor in the plasma membrane

In the present study we analyze the oligomerization of the 5-HT1A receptor within living cells at the sub-cellular level. Using a 2-excitation Förster Resonance Energy Transfer (FRET) method combined with spectral microscopy we are able to estimate the efficiency of energy transfer based on donor quenching as well as acceptor sensitization between CFP-and YFP-tagged 5-HT1A receptors at the plasma membrane. Through the analysis of the level of apparent FRET efficiency over the various relative amounts of donor and acceptor, as well as over a range of total surface expressions of the receptor, we verify the specific interaction of these receptors. Furthermore we study the role of acylation in this interaction through measurements of a palmitoylation-deficient 5-HT1A receptor mutant. Palmitoylation increases the tendency of a receptor to localize in lipid rich microdomains of the plasma membrane. This increases the effective surface density of the receptor and provides for a higher level of stochastic interaction

Molecular characteristics of carbapenemase-producing Enterobacterales in the Netherlands; results of the 2014–2018 national laboratory surveillance

Objectives: Carbapenem resistance mediated by mobile genetic elements has emerged worldwide and has become a major public health threat. To gain insight into the molecular epidemiology of carbapenem resistance in The Netherlands, Dutch medical microbiology laboratories are requested to submit suspected carbapenemase-producing Enterobacterales (CPE) to the National Institute for Public Health and the Environment as part of a national surveillance system. Methods: Meropenem MICs and species identification were confirmed by E-test and MALDI-TOF and carbapenemase production was assessed by the Carbapenem Inactivation Method. Of all submitted CPE, one species/carbapenemase gene combination per person per year was subjected to next-generation sequencing (NGS). Results: In total, 1838 unique isolates were received between 2014 and 2018, of which 892 were unique CPE isolates with NGS data available. The predominant CPE species were Klebsiella pneumoniae (n = 388, 43%), Escherichia coli (n = 264, 30%) and Enterobacter cloacae complex (n = 116, 13%). Various carbapenemase alleles of the same carbapenemase gene resulted in different susceptibilities to meropenem and this effect varied between species. Analyses of NGS data showed variation of prevalence of carbapenemase alleles over time with blaOXA-48 being predominant (38%, 336/892), followed by blaNDM-1 (16%, 145/892). For the first time in the Netherlands, blaOXA-181, blaOXA-232 and blaVIM-4 were detected. The genetic background of K. pneumoniae and E. coli isolates was highly diverse. Conclusions: The CPE population in the Netherlands is diverse, suggesting multiple introductions. The predominant carbapenemase alleles are blaOXA-48 and blaNDM-1. There was a clear association between species, carbapenemase allele and susceptibility to meropenem

National laboratory-based surveillance system for antimicrobial resistance: a successful tool to support the control of antimicrobial resistance in the Netherlands

An important cornerstone in the control of antimicrobial resistance (AMR) is a well-designed quantitative system for the surveillance of spread and temporal trends in AMR. Since 2008, the Dutch national AMR surveillance system, based on routine data from medical microbiological laboratories (MMLs), has developed into a successful tool to support the control of AMR in the Netherlands. It provides background information for policy making in public health and healthcare services, supports development of empirical antibiotic therapy guidelines and facilitates in-depth research. In addition, participation of the MMLs in the national AMR surveillance network has contributed to sharing of knowledge and quality improvement. A future improvement will be the implementation of a new semantic standard together with standardised data transfer, which will reduce errors in data handling and enable a more real-time surveillance. Furthermore, the

Increase in treatment of retinopathy of prematurity in the Netherlands from 2010 to 2017

Purpose: Compare patients treated for Retinopathy of Prematurity (ROP) in two consecutive periods. Methods: Retrospective inventory of anonymized neonatal and ophthalmological data of all patients treated for ROP from 2010 to 2017 in the Netherlands, subdivided in period (P)1: 1-1-2010 to 31-3-2013 and P2: 1-4-2013 to 31-12-2016. Treatment characteristics, adherence to early treatment for ROP (ETROP) criteria, outco