Visual Psychophysics and Physiological Optics Longitudinal Change and Stability of Refractive, Keratometric, and Internal Astigmatism in Childhood

PURPOSE. To assess longitudinal change in refractive, keratometric, and internal astigmatism in a sample of students from a population with a high prevalence of with-the-rule (WTR) astigmatism and to determine the optical origins of changes in refractive astigmatism. METHODS. A retrospective analysis of longitudinal measurements of right eye refractive and keratometric astigmatism in Tohono O'odham Native American children was conducted. Changes in refractive and keratometric astigmatism per year were compared in a younger cohort (n ¼ 1594, 3 to <11 years old) and an older cohort (n ¼ 648, 11 to <19 years old). Data were analyzed in clinical notation (Cyl) and vector notation (J0, J45). RESULTS. On average, refractive astigmatism (means: 1.19 diopters [D] Cyl, þ0.54 J0, þ0.03 J45) resulted primarily from WTR corneal astigmatism (means: þ0.85 J0, À0.02 J45) and against-the-rule (ATR) internal astigmatism (means: À0.31 J0, þ0.05 J45). Mean longitudinal changes in astigmatism were statistically significant (younger cohort À0.02 D/y Cyl; older cohort þ0.06 D/y Cyl). In the younger cohort, astigmatism decreased with age in low and moderate astigmats (<3.00 D) and increased with age in high astigmats ( ‡3.00 D). In the older cohort, astigmatism increased with age across all levels of astigmatism. Longitudinal changes in keratometric and internal astigmatism were negatively correlated in both cohorts. CONCLUSIONS. Cross-sectional data suggest the presence of a constant ATR contribution from internal astigmatism (0.60 D Cyl) that is close to the 0.50 D ATR constant reported by Javal and others. Highly astigmatic 3-to <11-year-old children and children older than age 11 years show a small (not clinically significant) increase in astigmatism with age. A negative correlation between changes in keratometric astigmatism and internal astigmatism suggests an active compensation that may contribute to the stability of astigmatism in Tohono O'odham children. Keywords: astigmatism, refractive error development, children, Native American R esearch conducted over the past 15 years has yielded a large longitudinal database on refractive development in Tohono O'odham children. There is a high prevalence of astigmatism among elementary school children who are members of this Native American tribe. 1-4 The high prevalence of refractive astigmatism in Tohono O'odham children is present in infancy and persists at least through elementary school. 1,2,4-7 A longitudinal study of corneal astigmatism in 960 Tohono O'odham children aged 6 months through 7 years showed that in early development (6 months to <3 years), astigmatism decreased in children with high astigmatism (À0.37 diopters [D]/y) and remained stable in children with little or no astigmatism (þ0.05 D/y). 7 From age 3 through 7 years, astigmatism decreased in children with both high astigmatism (À0.11 D/y) and low/no astigmatism (À0.03 D/y). 7 A detailed account of changes in astigmatism beyond age 7 years in this population has not yet been reported. However, a recent report on change in spherical equivalent (M) in a longitudinal sample of Tohono O'odham students ages 3 to 18 years showed that rate of change in M with age was significantly greater for children who were hyperopic (M ‡ þ2.00) prior to age 5.5 years, consistent with continued emmetropization into the school years. In addition, higher levels of refractive astigmatism were associated with predicted myopia onset (M À0.75 D) by age 18 years. 9 This relation, specifically the relation between keratometric and refractive (total) astigmatism, was originally described by Javal in 1890 10,11 : Refractive Astigmatism ¼ 1.25(Keratometric Astigmatism) À 0.50 D 3 90. A more recent empirically based modification of Javal's rule suggests that WTR and ATR refractive astigmatism can be predicted by subtracting an ATR constant (0.50 D) from the magnitude of keratometric astigmatism, with little or no adjustment based on magnitude of keratometric astigmatism. 10 Little is known about how the relation between keratometric and internal astigmatism changes with development in childhood. For example, it is not known if magnitude of AT

Convergence Insufficiency, Accommodative Insufficiency, Visual Symptoms, and Astigmatism in Tohono O’odham Students

Purpose. To determine rate of convergence insufficiency (CI) and accommodative insufficiency (AI) and assess the relation between CI, AI, visual symptoms, and astigmatism in school-age children. Methods. 3rd–8th-grade students completed the Convergence Insufficiency Symptom Survey (CISS) and binocular vision testing with correction if prescribed. Students were categorized by astigmatism magnitude (no/low: <1.00 D, moderate: 1.00 D to <3.00 D, and high: ≥3.00 D), presence/absence of clinical signs of CI and AI, and presence of symptoms. Analyses determine rate of clinical CI and AI and symptomatic CI and AI and assessed the relation between CI, AI, visual symptoms, and astigmatism. Results. In the sample of 484 students (11.67 ± 1.81 years of age), rate of symptomatic CI was 6.2% and symptomatic AI 18.2%. AI was more common in students with CI than without CI. Students with AI only (p=0.02) and with CI and AI (p=0.001) had higher symptom scores than students with neither CI nor AI. Moderate and high astigmats were not at increased risk for CI or AI. Conclusions. With-the-rule astigmats are not at increased risk for CI or AI. High comorbidity rates of CI and AI and higher symptoms scores with AI suggest that research is needed to determine symptomatology specific to CI

A simple radionuclide-driven single-ion source

We describe a source capable of producing single barium ions through nuclear recoils in radioactive decay. The source is fabricated by electroplating 148Gd onto a silicon {\alpha}-particle detector and vapor depositing a layer of BaF2 over it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+ ions from the BaF2 layer and emit them in the surrounding environment. The simultaneous detection of an {\alpha} particle in the substrate detector allows for tagging of the nuclear decay and of the Ba+ emission. The source is simple, durable, and can be manipulated and used in different environments. We discuss the fabrication process, which can be easily adapted to emit most other chemical species, and the performance of the source

Search for Neutrinoless Double-Beta Decay in 136^{136}Xe with EXO-200

We report on a search for neutrinoless double-beta decay of $^{136}$Xe with EXO-200. No signal is observed for an exposure of 32.5 kg-yr, with a background of ~1.5 x 10^{-3} /(kg yr keV) in the $\pm 1\sigma$ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay $T_{1/2}^{0\nu\beta\beta}$($^{136}$Xe) > 1.6 x 10$^{25}$ yr (90% CL), corresponding to effective Majorana masses of less than 140-380 meV, depending on the matrix element calculation

A magnetically-driven piston pump for ultra-clean applications

A magnetically driven piston pump for xenon gas recirculation is presented. The pump is designed to satisfy extreme purity and containment requirements, as is appropriate for the recirculation of isotopically enriched xenon through the purification system and large liquid xenon TPC of EXO-200. The pump, using sprung polymer gaskets, is capable of pumping more than 16 standard liters per minute (SLPM) of xenon gas with 750 torr differential pressure.Comment: 6 pages, 5 figure

Investigation of radioactivity-induced backgrounds in EXO-200

The search for neutrinoless double-beta decay (0{\nu}{\beta}{\beta}) requires extremely low background and a good understanding of their sources and their influence on the rate in the region of parameter space relevant to the 0{\nu}{\beta}{\beta} signal. We report on studies of various {\beta}- and {\gamma}-backgrounds in the liquid- xenon-based EXO-200 0{\nu}{\beta}{\beta} experiment. With this work we try to better understand the location and strength of specific background sources and compare the conclusions to radioassay results taken before and during detector construction. Finally, we discuss the implications of these studies for EXO-200 as well as for the next-generation, tonne-scale nEXO detector.Comment: 9 pages, 7 figures, 3 table