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The ultrafast reversibility of changes to the electronic structure and electric polarizability of a dielectric with the electric field of a laser pulse, demonstrated here, offers the potential for petahertz-bandwidth optical signal manipulation. Dielectrics turned conductor in a flash Two studies published in this issue highlight the potential for ultrafast signal manipulation in dielectrics using optical fields. When it comes to electrical signal processing, semiconductors have become the materials of choice. However, insulators such as dielectrics could be attractive alternatives: they have a fast response in principle, but usually have extremely low conductivity at low electric fields and break down in large fields. The electronic properties of dielectrics can be controlled with few-cycle laser pulses that permit damage-free exposure of dielectrics to high electric fields. Agustin Schiffrin et al . demonstrate that strong optical laser fields with controlled few-cycle waveforms can reversibly transform a dielectric insulator into a conductor within the optical period (within one femtosecond). Martin Schultze et al . address the crucial issue of ultrafast reversibility, demonstrating that the dielectric can be repeatedly switched 'on' and 'off' with light fields, without degradation. The control of the electric and optical properties of semiconductors with microwave fields forms the basis of modern electronics, information processing and optical communications. The extension of such control to optical frequencies calls for wideband materials such as dielectrics, which require strong electric fields to alter their physical properties 1 , 2 , 3 , 4 , 5 . Few-cycle laser pulses permit damage-free exposure of dielectrics to electric fields of several volts per ångström 6 and significant modifications in their electronic system 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 . Fields of such strength and temporal confinement can turn a dielectric from an insulating state to a conducting state within the optical period 14 . However, to extend electric signal control and processing to light frequencies depends on the feasibility of reversing these effects approximately as fast as they can be induced. Here we study the underlying electron processes with sub-femtosecond solid-state spectroscopy, which reveals the feasibility of manipulating the electronic structure and electric polarizability of a dielectric reversibly with the electric field of light. We irradiate a dielectric (fused silica) with a waveform-controlled near-infrared few-cycle light field of several volts per angström and probe changes in extreme-ultraviolet absorptivity and near-infrared reflectivity on a timescale of approximately a hundred attoseconds to a few femtoseconds. The field-induced changes follow, in a highly nonlinear fashion, the turn-on and turn-off behaviour of the driving field, in agreement with the predictions of a quantum mechanical model. The ultrafast reversibility of the effects implies that the physical properties of a dielectric can be controlled with the electric field of light, offering the potential for petahertz-bandwidth signal manipulation.

Background Limited data exist collating most of the associated factors for strabismus in one analysis. The aim of this study was to assess the prevalence of strabismus and to analyse associated factors in former preterm and full-term infants. Methods In this cross-sectional study, 239 former preterm infants with gestational age (GA) ≤ 32 weeks and 264 former full-term born infants with GA ≥ 37 weeks underwent detailed ophthalmologic examination in the age of 4–10 years and perinatal data assessment for risk factor analysis. Ophthalmologic examinations included cover testing, best corrected visual acuity, cycloplegic objective refraction, slit lamp as well as fundus examinations. For association analysis with strabismus, the following data was collected and included in multivariable analysis: sex, age at examination, anisometropia, myopic and hyperopic refractive error (≥ 3 dioptres), astigmatism, birth weight percentile, gestational age, retinopathy of prematurity occurrence, maternal age at childbirth, mother smoking, breastfeeding < 3 months, artificial ventilation, intraventricular bleeding, and other perinatal adverse events. Results Overall, 4/264 (2%) full-term infants, 15/125 (12%) preterm-infants with GA 29–32 weeks without ROP, 13/59 (22%) preterm infants with GA ≤ 28 weeks without ROP and 14/55 (26%) with GA ≤ 32 weeks with retinopathy of prematurity were affected by strabismus. In the multivariable regression model strabismus was associated with GA (OR = 0.84 per week; p  = 0.001), hyperopic refractive error (OR = 4.22; p  = 0.002) and astigmatism (OR = 1.68; p  = 0.02). Conclusion This investigation highlights that low gestational age and refraction of the eye are independent risk factors for strabismus, while the other factors show less independent influence.

Objective To analyse macular retinal and choroidal layer thickness in former preterm and full-term infants and to assess associated perinatal influence factors and functional correlation. Methods This prospective controlled, cross-sectional, hospital-based study in a tertiary center of maximum care examined former preterm infants with a gestational age (GA) ≤ 32 weeks and full-term neonates currently aged 4 to 10 years. We investigated data from 397 infants, analysing total foveal retinal thickness and six distinct macular retinal layer and choroidal layer measurements via spectral-domain optical coherence tomography. Multivariable linear regression analysis was performed to investigate associations of layer thickness with GA and retinopathy of prematurity (ROP). Results Total retinal thickness in the fovea was thicker in former preterm infants with GA ≤ 28 weeks and in those with GA between 29–32 weeks compared to full-term infants independently of ROP. Occurrence of ROP was also associated with increased foveal thickness. Ganglion cell layer together with inner plexiform layer (GCL+IPL) was thinner in infants with GA ≤ 28 weeks than in full-term infants at 1000 and 2000μm distance from the fovea, but no association with ROP was present. Similar results were found for the photoreceptor layer. Total foveal retinal thickness was associated with low visual function. Conclusion This study identified low gestational age and ROP occurrence as main determinants for foveal thickening. Furthermore, thinned GCL+IPL measurements were associated with lower gestational age. This study highlights the prognostic value of these maturity parameters influencing retinal morphology, which may affect visual function.

PurposeThe aim of the study was to investigate peripapillary retinal nerve fibre layer thickness (RNFLT) in former preterm infants and full-term neonates using spectral-domain optical coherence tomography (SD-OCT).MethodsThe prospective, controlled, cross-sectional, hospital-based study in a tertiary centre with maximum care examined 503 infants with a former gestational age (GA) of ≥37 and ≤32 weeks now aged between 4 and 10 years. In total, we analysed 432 participants with successful circular peripapillary RNFLT OCT measurements. Main outcome measures were RNFLT correlations to GA, birth weight, occurrence of retinopathy of prematurity (ROP), perinatal adverse events as well as functional correlation.ResultsGlobal RNFLT was thinner in infants with GA ≤28 weeks compared with infants with GA between 29 and 32 weeks (p=0.024), and to full-term neonates (p=0.007) independent of the occurrence of ROP. Multivariable analysis revealed that RNFLT was positively associated with higher birth weight and GA. Furthermore, a decrease of RNFLT was related to reduced visual function in all peripapillary sectors.ConclusionsThe main factors for retinal nerve fibre layer thinning are low birth weight and low GA. In addition, decreased RNFLT was associated with reduced visual function. This demonstrates that preterm infants are at high risk for peripapillary RNFL damage associated with reduced visual function.

Purpose: Low birth weight (BW) is associated with altered ocular geometry such as a steeper corneal shape in adulthood. However, it is unclear whether low birth weight affects corneal thickness development in the center or periphery in adulthood which may contribute to ocular disease. The purpose of this study was to investigate corneal thickness in former low birth weight individuals in adulthood. Methods: The German Gutenberg Health Study is a prospective, population-based study in which every participant (age range 40–80 years) was measured with Scheimpflug imaging (Pentacam HR, Oculus Optikgeräte GmbH, Wetzlar, Germany). BW was collected by self-reports. The relationship between birth weight and corneal thickness at different locations were assessed. Linear regression models were carried out including uni- and multivariable analyses with adjustment for age, sex, mean corneal radius, and white-to-white distance. Main outcome measures were corneal thickness at the apex, at the pupil center, and at the corneal periphery. Results: Overall, 5657 participants were successfully measured (3019 females, aged 56.0 ± 10.3 years). In multivariable analyses a lower BW was associated with a thinner corneal thickness at the apex (B = 1.71 µm/500 g, p < 0.001) and at the pupil (B = 1.69 µm/500 g, p < 0.001). These effects diminished towards the corneal periphery resulting in no differences in the perilimbal regions. Conclusion: The present study provides evidence that lower birth weight goes along with corneal thickness alterations even into adult ages of 40 to 80 years. Thinner measurements of the cornea were particularly found in the corneal center and diminished in the periphery. This indicates that there may be fetal origins affecting corneal thickness development particularly in the corneal center.