Appearance of SERS activity in single silver nanoparticles by laser-induced reshaping.

We report simultaneous plasmonic scattering and Raman spectroscopic observations of single citrate capped silver nanoparticles (AgNPs) which exhibit surface enhanced Raman scattering (SERS) upon meeting specific conditions induced by laser (532 nm) exposure. We show that nanoparticles which are not initially SERS active become SERS active by laser-induced reshaping/reorientation. A set-up developed for these observations enabled in situ high speed time-lapse characterization using plasmonic and Raman spectroscopies in conjunction with dark-field microscopy (DFM). Changes in the AgNPs were confirmed by monitoring plasmonic scattering spectra and DFM images. Time-lapse observations have shown that laser-induced changes in the plasmonic properties of AgNPs resulted in the appearance of SERS. Spectral matching between plasmon resonance and downward molecular vibronic transitions for molecules adsorbed on the surface of plasmonic nanomaterials is attributed to the nanoparticle SERS. We have further shown that the release of silver ions by silver nanoparticles can be the probable reason for their plasmonic changes. Gold nanoparticles inert to such mild (850 µW, 532 nm) laser-induced changes do not exhibit the appearance of SERS.

Dual Probe Sensors Using Atomically Precise Noble Metal Clusters.

This article adds a new direction to the functional capability of protein-protected atomically precise gold clusters as sensors. Counting on the extensively researched intense luminescence of these clusters and considering the electron donating nature of select amino acids, we introduce a dual probe sensor capable of sensing changes in luminescence and conductivity, utilizing bovine serum albumin-protected atomically precise gold clusters hosted on nanofibers. To this end, we have also developed a hybrid nanofiber with a conducting core with a porous dielectric shell. We show that clusters in combination with nanofibers offer a highly selective and sensitive platform for the detection of trace quantities of trinitrotoluene, both in solution and in the vapor phase. In the solution phase, trinitrotoluene (TNT) can be detected down to 1 ppt at room temperature, whereas in vapor phase, 4.8 × 109 molecules of TNT can be sensed using a 1 mm fiber. Although the development in electrospinning techniques for fabricating nanofibers as sensors is quite substantial, a hybrid fiber with the dual properties of conductivity and luminescence has not been reported yet.

Preoperative visual acuity and contrast sensitivity in children with small, partial, or non-central cataracts.

BACKGROUND: While there is clear evidence that dense central cataracts >3 mm diameter warrant prompt intervention to prevent deprivation amblyopia, guidelines for management of small, partial and non-central cataracts are not evidence-based. Consensus guidelines advise managing affected infants and preschool children by monitoring for possible progression in size or density and pharmacologic pupillary dilation, if indicated. Extraction is deemed necessary if the cataract progresses sufficiently to obscure the visual axis or if strabismus or nystagmus develops. We evaluated the long-term visual acuity outcome of the consensus guidelines and whether sensory testing during infancy and early childhood may be helpful in guiding treatment. METHODS: A total of 40 consecutive children diagnosed with small, partial, or non-central cataracts at 1 week to 2.5 years of age were enrolled in a prospective study of forced-choice preferential looking visual acuity and contrast sensitivity development. Long-term visual acuity outcome was assessed by crowded HOTV or ETDRS at 4-11 years. RESULTS: Of the 40 children managed by consensus guidelines, 24 (60%) had abnormal visual acuity at 4-11 years of age, including 9 (23%) who had moderate to severe visual impairment (20/80 or worse) in 1 or both eyes. Abnormal visual acuity and contrast sensitivity during development were predictive of abnormal long-term visual acuity outcomes. CONCLUSIONS: Visual acuity and contrast sensitivity tests were sensitive to the effects of visual deprivation on the developing visual system and may be useful in early identification of children with small, partial, or non-central cataracts who could benefit from cataract extraction.

Fixation instability in anisometropic children with reduced stereopsis.

BACKGROUND: Hyperopic anisometropia in children can be associated with abnormal stereoacuity and "microstrabismus," a small temporalward "flick" as each eye assumes fixation on cover testing. The prevailing hypothesis is that abnormal sensory experience leads to foveal suppression and, subsequently, secondary microstrabismus. This study investigated the hypothesis that disruption of bifoveal fusion by anisometropia directly affects ocular motor function. METHODS: A total of 94 children with hyperopic anisometropia (ages 5-13 years) were evaluated prospectively between June 2010 and December 2012 with the use of the Nidek MP-1 microperimeter. Fixation instability was quantified by the area of the bivariate contour ellipse that included 95% of fixation points during a 30-second test interval. Each eye movement waveform during the 30-second test interval also was examined with the use of custom software and classified as normal, fusion maldevelopment nystagmus (FMNS), or infantile nystagmus. Finally, the Randot Preschool Stereoacuity Test (Stereo Optical Company Inc, Chicago, IL) was administered. RESULTS: Stereoacuity was correlated with fixation instability (Spearman r = 0.50; 95% CI, 0.33-0.64); visual acuity was more weakly correlated (r = 0.28). All children with normal stereoacuity had stable fixation, children with subnormal stereoacuity had fixation instability, and those with nil stereoacuity had the most instability. Eye movement records during attempted fixation were of sufficient quality for classification in 81 children; 61% of those with reduced stereoacuity and 88% of those with nil stereoacuity had FMNS eye movement waveforms. CONCLUSIONS: Our data support the hypothesis that the binocular decorrelation caused by anisometropia can disrupt ocular motor development, resulting in FMNS and its temporalward refoveating "flicks" that may mimic microstrabismus.

A quantitative study of fixation stability in amblyopia.

PURPOSE: To determine whether fixation instability contributes to reduced visual acuity in amblyopia, we compared fixation instability, quantified by the Nidek MP-1 microperimeter, in amblyopic and nonamblyopic children. METHODS: Participants were 89 children (5-17 years old) with strabismus (n = 31), anisometropia (n = 29), or both conditions (n = 29). Fixation instability was measured using the Nidek MP-1 microperimeter, which calculated horizontal and vertical eye position at 25 Hz as the child attempted steady fixation for 30 seconds. Fixation instability was quantified as the 95% bivariate contour ellipse area (95% BCEA), the best-fit ellipse within which 95% of fixation occurred during the 30-second test. BCEA was normalized by log transformation. RESULTS: Children with amblyopia had significantly larger BCEAs for amblyopic eyes (mean = 0.56 log deg(2)) than fellow eyes (mean = 0.2 log deg(2), P < 0.01) and right eyes of normal controls (mean = 0.12 log deg(2), P ≤ 0.01). Fixation instability was significantly greater along the horizontal axis of the ellipse for amblyopic (mean = 3.53°) than fellow (mean = 1.98°, P = 0.008), and control (mean = 1.62°, P < 0.001) eyes. CONCLUSIONS: Fixation instability in amblyopic eyes of children with strabismus and/or anisometropia, and the associated poor stereoacuity probably is the consequence of decorrelated binocular experience early in life. Longer duration of decorrelated visual experience is associated with increased fixation instability, poorer stereoacuity, and more severe amblyopia. Treatments that minimize the duration of decorrelated visual experience may improve stereoacuity and decrease fixation instability.

Visual acuity assessment of children with special needs.

INTRODUCTION AND PURPOSE: A number of studies have evaluated visual acuity (VA) of special needs children, but no analyses of the parents' perception of VA testing or the utilization of VA test results by pediatric ophthalmologists have been reported. PATIENTS AND METHODS: Special needs children referred for an initial VA test (Teller Acuity Cards) during a 2-year period were enrolled (n = 309). Within the overall cohort, twenty consecutive parents whose child attended during a 6-week period completed a Parent Questionnaire before and after VA testing. Also, 58 parents of infants with cortical visual impairment (CVI) completed the Parental Stress Index-Short Form (PSI-SF) before VA testing and 3 months later. Referring pediatric ophthalmologists (n = 12) completed a Physician Questionnaire. RESULTS: VA testing was associated with parents reporting increased knowledge scores and decreased concerns about their children's vision on the Parent Questionnaire. VA testing was also associated with reduced Total and Parental Distress subscale scores on the PSI-SF by parents of infants with CVI. Ophthalmologists reported that VA results were useful in diagnosis and clinical management and provided new information to parents, Early Childhood Intervention programs, schools, and social agencies. CONCLUSION: VA testing is of benefit in children with special needs to both their parents and ophthalmologists, providing quantitative information about visual impairment and reducing stress experienced by parents.

Abnormal radial deformation hyperacuity in children with strabismic amblyopia.

PURPOSE: In infants and toddlers, letter acuity is not a useful option, and grating acuity may underestimate the depth of strabismic amblyopia. Here, as a first step to establish the effectiveness of the paradigm as a clinical test, we assessed if radial deformation hyperacuity, known to be severely disrupted in adults with strabismic amblyopia, could be a potential test to detect and monitor strabismic amblyopia in young children. METHODS: Fifty-one strabismic children and 130 normal controls ages 3 to 17 years participated. Radial deformation hyperacuity with three different radial frequency (RF) patterns (1° radius 8 RF, 0.5° radius 8 RF, and 1° radius 16 RF), optotype acuity, and grating acuity were measured. For strabismic children, hyperacuity and grating acuity were identified as normal/amblyopic based on age-matched norms. The normal/abnormal classification was compared with amblyopia diagnosis by gold standard early treatment diabetic retinopathy study (ETDRS) optotype visual acuity. RESULTS: The 0.5° radius 8 RF pattern had 83% sensitivity and 71% positive predictive value (PPV) for strabismic amblyopia. In comparison, the 1° radius 8 RF and 1° radius 16 RF patterns had poorer sensitivity (27%-12%) and PPV (57%-50%) for amblyopia, similar to grating acuity (sensitivity = 38%, PPV = 31%). Amblyopic deficits using the 0.5° radius 8 RF pattern were directly proportional to optotype visual acuity deficits. CONCLUSIONS: The demonstrated feasibility of radial deformation stimuli for forced-choice preferential looking testing and the sensitivity and specificity of the small radius radial deformation hyperacuity stimulus for amblyopia support the potential to utilize this test to detect and monitor amblyopia in infants and preschool children.

Quantifying nystagmus in infants and young children: relation between foveation and visual acuity deficit.

PURPOSE: Nystagmus eye movement data from infants and young children are often not suitable for advanced quantitative analysis. A method was developed to capture useful information from noisy data and validate the technique by showing meaningful relationships with visual functioning. METHODS: Horizontal eye movements from patients (age 5 months-8 years) with idiopathic infantile nystagmus syndrome (INS) were used to develop a quantitative outcome measure that allowed for head and body movement during the recording. The validity of this outcome was assessed by evaluating its relation to visual acuity deficit in 130 subjects, its relation to actual fixation as assessed under simultaneous fundus imaging, its correlation with the established expanded nystagmus acuity function (NAFX), and its test-retest variability. RESULTS: The nystagmus optimal fixation function (NOFF) was defined as the logit transform of the fraction of data points meeting position and velocity criteria within a moving window. A decreasing exponential relationship was found between visual acuity deficit and the NOFF, yielding a 0.75 logMAR deficit for the poorest NOFF and diminishing deficits with improving foveation. As much as 96% of the points identified as foveation events fell within 0.25° of the actual target. Good correlation (r = 0.96) was found between NOFF and NAFX. Test-retest variability was 0.49 logit units. CONCLUSIONS: The NOFF is a feasible method to quantify noisy nystagmus eye movement data. Its validation makes it a promising outcome measure for the progression and treatment of nystagmus during early childhood.

Symptomatic ascites in a patient with hypothyroidism of short duration.

Symptomatic ascites as a presenting symptom of hypothyroidism is quite rare. In most of the case reports, patients with ascites requiring therapeutic abdominal paracentesis have long-standing hypothyroidism. We present a case of symptomatic ascites in a subject with hypothyroidism following radioiodine therapy for Graves disease. A 70-year-old African-American man presented with increasing weakness, shortness of breath, weight gain, constipation, and abdominal distention. Past history was significant for coronary artery disease, diabetes, hypertension and history of radioiodine therapy for Graves disease 9 months prior to the presentation. He was taking levothyroxine at 50 microg per day for 3 months prior to the presentation. Physical examination findings were significant for puffiness around the eyes, decreased breath sounds at the lung bases, and distended abdomen with free fluid, hung-up reflexes, and cold extremities. The thyroid-stimulating hormone level at the time was 64 with a free T4 less than 0.4 ng/dL. Analysis of the ascitic fluid revealed an exudative effusion with a serum to ascitic fluid albumin gradient of 1.2. The patient required therapeutic abdominal paracentesis twice, with 4 L each time, to relieve the symptoms. Work-up to rule out other causes did not reveal any other relevant abnormality. After initiation of thyroid hormone replacement, the patient responded very well and the ascites resolved within 2 months. We conclude that ascites associated with hypothyroidism is rare but must be recognized early, since thyroid replacement is the definitive therapy.