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Biomedical subjects

C A Johnson

Publications and source records attributed to C A Johnson.

At least 55 records · Page 3Linked to original sources
PubMed2001

Frequency doubling perimetry using a liquid crystal display.

PURPOSE: To compare frequency doubling contrast thresholds using a new liquid crystal window display with those obtained with the commercial video-based Frequency Doubling Technology perimeter. METHODS: One eye of 49 glaucoma patients and one eye of 49 normal controls were tested with the liquid crystal window and Frequency Doubling Technology systems. Both displays employed identical stimulus conditions and test strategies, although the dynamic range of the liquid crystal window-based display was approximately 30% smaller than that of the Frequency Doubling Technology system. Measurements were repeated using the video-based Frequency Doubling Technology perimeter in a subset of 21 eyes. Relationships between and within displays were assessed using a chance-corrected agreement measure (quadratic weighted kappa) and paired measurement differences. Variability was quantified using standard deviation from the mean paired measurement difference. RESULTS: Over the restricted operating range of the liquid crystal display system, between-display and within-video display variability was 2.3 dB and 3.2 dB, respectively, between-display agreement was 0.66, and within-display agreement (test-retest for Frequency Doubling Technology) was 0.65. CONCLUSIONS: Levels of agreement and variability between the two frequency doubling displays were of similar magnitude to repeated (test-retest) Frequency Doubling Technology measures, suggesting that contrast threshold measurements made using the two displays may be used interchangeably. However, the operating range of the current liquid crystal window-based display is smaller.

Aged↗
PubMed2001

Incidence and prevalence of short wavelength automated perimetry deficits in ocular hypertensive patients.

PURPOSE: To determine the prevalence and incidence of short wavelength automated perimetry deficits in comparison to standard automated perimetry deficits in patients with ocular hypertension. METHODS: Five hundred eyes of 250 patients with ocular hypertension were recruited into a prospective, longitudinal study and tested with standard automated perimetry and short wavelength automated perimetry annually for 5 years. Both eyes of 60 normal subjects, 21 to 85 years of age, were used to establish normative data for short wavelength automated perimetry and standard automated perimetry. This allowed independent evaluation of left and right eyes of patients. All normal data were corrected for age, and short wavelength automated perimetry results were corrected for lens transmission. The lowest fifth and first percentiles for the normal observers were derived for the 10 glaucoma hemifield test zones for short wavelength automated perimetry and standard automated perimetry. Visual fields were considered outside normal limits if two glaucoma hemifield test zones were below the normal fifth percentile or one glaucoma hemifield test zone was below the normal first percentile. RESULTS: Baseline prevalence of short wavelength automated perimetry and standard automated perimetry deficits were 9.4% and 1.4%, respectively. During the study, incident rates of field loss were 6.2% (1.23% per year) for short wavelength automated perimetry and 5.9% (1.18% per year) for standard automated perimetry. Once abnormal, 80% of short wavelength automated perimetry fields remained abnormal on the next examination, whereas only 45% of abnormal standard automated perimetry fields remained abnormal. New short wavelength automated perimetry deficits in ocular hypertensives were more prominent and more persistent than new standard automated perimetry deficits. CONCLUSIONS: Our findings are consistent with the interpretation that short wavelength automated perimetry deficits occur before standard automated perimetry deficits in glaucoma. The similar incidence rates suggest that both standard automated perimetry and short wavelength automated perimetry are monitoring the same underlying glaucomatous disease process.

Adult↗
PubMed2001

Computerized method of visual acuity testing: adaptation of the amblyopia treatment study visual acuity testing protocol.

PURPOSE: To report a computerized method for determining visual acuity in children using the Amblyopia Treatment Study visual acuity testing protocol. METHODS: A computerized visual acuity tester was developed that uses a programmed handheld device that uses the Palm operating system (Palm, Inc, Santa Clara, California). The handheld device communicates with a personal computer running a Linux operating system and 17-inch monitor. At a test distance of 3 m, single letters can be displayed from 20/800 to 20/12. A C program on the handheld device runs the Amblyopia Treatment Study visual acuity testing protocol. Using this method, visual acuity was tested in both the right and left eyes, and then the testing was repeated in 156 children age 3 to 7 years at four clinical sites. RESULTS: Test-retest reliability was high (r =.92 and 0.95 for and right and left eyes, respectively), with 88% of right eye retests and 94% of left eye retests within 0.1 logarithm of minimal angle of resolution (logMAR) units of the initial test. The 95% confidence interval for an acuity score was calculated to be the score +/- 0.13 logMAR units. For a change between two acuity scores, the 95% confidence interval was the difference +/- 0.19 logMAR units. CONCLUSIONS: We have developed a computerized method for measurement of visual acuity. Automation of the Amblyopia Treatment Study visual acuity testing protocol is an effective method of testing visual acuity in children 3 to 7 years of age.

Amblyopia↗
PubMed2001

Psychophysical measurement of glaucomatous damage.

Within the past twenty years, a number of new psychophysical test procedures have been adapted for use in perimetry and visual field testing. These procedures are designed to measure the functional properties of different types of retinal ganglion cell subpopulations. Although many of these new procedures exhibit better performance characteristics than standard automated perimetry, no single test procedure appears to be decidedly superior to all others. Comparison of multiple functions in patients with early glaucomatous damage suggests that visual function losses are not selective for specific retinal ganglion cell subpopulations in all patients. For evaluation of the efficacy of neuroprotective agents in glaucoma, one of the challenges facing the development of new psychophysical tests is to be able to distinguish visual function losses that are due to ganglion cell drop-out ("dead" cells) from those that are due to malfunctioning retinal nerve fibers ("sick" cells).

Glaucoma↗
PubMed2001

Synthesis and antifolate evaluation of the aminopterin analogue with a bicyclo.

N-[4-[[2,4-diamino-6-pteridinyl)methyl]amino]bicyclo[2.2.2]octane-1-carbonyl]-L-glutamic acid (1) was synthesized and tested for antifolate activity. N-(4-Aminobicyclo[2.2.2]octane-1-carbonyl-L-glutamic acid dimethyl ester (6), the side chain precursor to subject compound 1, was synthesized readily via reported bicyclo[2.2.2]octane-1,4-dicarboxylic acid monoethyl ester (2). The side chain precursor 6 was alkylated by 6-(bromomethyl)-2,4-pteridinediamine (7). Subsequent ester hydrolysis then afforded 1. Antifolate and antitumor evaluation of 1 verses L1210 dihydrofolate reductase (DHFR) and three tumor cell lines (L1210, S180, and HL60) showed it to be ineffective. Although compound 1 was very similar to aminopterin structurally, the bicyclo[2.2.2]octane ring system in place of the phenyl ring in the p-aminobenzoate moiety effectively negates the stoichiometric binding displayed by many classical DHFR inhibitors bearing appropriate aromatic ring systems in the side chain.

Aminopterin↗
PubMed2001

Subcutaneous erythropoietin results in lower dose and equivalent hematocrit levels among adult hemodialysis patients: Results from the 1998 End-Stage Renal Disease Core Indicators Project.

The National Kidney Foundation's Dialysis Outcome Quality Initiative (NKF-DOQI) guidelines recommend that epoetin alfa should be administered by the subcutaneous route in hemodialysis patients. We determined whether hematocrit levels in hemodialysis patients differed by route of epoetin alfa administration after controlling for demographic factors and iron status. Data were available for 7,092 of the 7,658 patients randomly chosen for inclusion in the 1997 Health Care Financing Administration Core Indicators sample. Epoetin alfa was administered to 96% of the study cohort and was administered subcutaneously in 10% of patients. After controlling for hematocrit, patient characteristics, adequacy of dialysis, iron status, serum albumin, postdialysis weight, and duration of dialysis, the epoetin alfa dose by the intravenous route was 193.6 units/kg/wk (95% confidence interval, 189.5 to 197.8 units/kg/wk) compared with 167.4 units/kg/wk (95% confidence interval, 153.9 to 180.8 units/kg/wk) for the subcutaneous route (P < 0.001). The mean hematocrit for the subcutaneous route was 32.7% +/- 3.4% and for the intravenous route was 33.0% +/- 3.2% (P < 0.05). Factors independently associated with increased hematocrit included male gender, white race, older patient age, greater number of years on dialysis, higher serum albumin concentration, higher urea reduction ratio, and percent transferrin saturation (all P < 0.001). After controlling for patient factors and weekly epoetin alfa dose, there was no association between route of epoetin alfa administration and hematocrit level (P = 0.144). Patients receiving epoetin alfa by the subcutaneous route had comparable hematocrit values using a lower epoetin alfa dose than patients receiving epoetin alfa intravenously. These data support the NKF-DOQI recommendation that epoetin alfa be administered subcutaneously in long-term hemodialysis patients.

Age Factors↗
PubMed2001

Changes in the cuticular hydrocarbon profile of the slave-maker ant queen, Polyergus breviceps emery, after killing a Formica host queen (Hymenoptera: Formicidae).

Queens of the slave-maker ant, Polyergus breviceps, take over nests of their Formica host species by fatally attacking the resident queen. As workers only begin grooming the P. breviceps queen once she has ceased her attack, we investigated whether a change in parasite queen chemistry may account for the change in worker behavior. Cuticular hydrocarbon profiles of newly mated P. breviceps queens and of queens of their two Formica host species were found to be species-specific. Profiles of newly mated P. breviceps queens that had attacked a Formica queen, however, were virtually identical to the queen profile of the species killed. Mass spectral analysis revealed that the hydrocarbons on the cuticles of newly mated P. breviceps changed from primarily normal alkanes to methyl and di-methyl branched alkanes after attacks. The results suggest that cuticular compounds from the host queen were transferred to the parasite queen during their aggressive interaction.

Aggression↗
PubMed2001

On-line sulfur isotope analysis of organic material by direct combustion: preliminary results and potential applications.

Sulfur isotopes have received little attention in ecology studies because plant and animal materials typically have low sulfur concentrations (< 1 wt.%) necessitating labor-intensive chemical extraction prior to analysis. To address the potential of direct combustion of organic material in an elemental analyzer coupled with a mass spectrometer, we compared results obtained by direct combustion to results obtained by sulfur extraction with Eschka's mixture. Direct combustion of peat and animal tissue gave reproducibility of better than 0.5/1000 and on average, values are 0.8/1000 higher than values obtained by Eschka extraction. Successful direct combustion of organic material appears to be a function of sample matrix and sulfur concentration. Initial results indicate that direct combustion provides fast, reliable results with minimal preparation. Pilot studies underway include defining bear diets and examining fluctuations between freshwater and brackish water in coastal environments.

Ecosystem↗
PubMed2001

Ethnic variation in peer influences on adolescent smoking.

Previous research has indicated that the influence of peers on adolescent smoking may differ across ethnic groups. Although many studies have focused on African Americans, Hispanics, and Whites, few studies have included Asian Americans, Pacific Islanders, and multi-ethnic adolescents as distinct groups. Using data from a statewide sample of 5870 eighth-grade adolescents in California, this study examined ethnic differences in the association between peer influence variables and smoking behavior and susceptibility. Informational peer influence (best friends' smoking behavior) and normative peer influence (prevalence estimates of peer smoking) were investigated. We hypothesized that informational peer influences would be stronger among Whites (whose families originate primarily from the individualistic cultures of the USA and Western Europe) than among Asian Americans, Pacific Islanders, Hispanics, and African Americans (whose families originate primarily from collectivist cultures). Conversely, we hypothesized that normative peer influences would be stronger among ethnic minority adolescents from collectivist cultural backgrounds than among Whites. Consistent with previous studies, friends' smoking and prevalence estimates of peer smoking were risk factors for past 30-day smoking and susceptibility to smoking across ethnic groups. The influence of friends' smoking behavior was stronger among Whites than among several other groups: Pacific Islanders, African Americans, and Hispanic/Latinos. The influence of prevalence estimates of peer smoking was stronger among Whites than among multiethnic adolescents. Results indicate that cultural factors may play a role in peer influences on smoking initiation. Smoking prevention interventions for adolescents should address the differences in peer influences across ethnic groups.

Adolescent↗
PubMed2001

Operative management of neuromatous knee pain: patient selection and outcome.

The management of intractable knee pain secondary to neuromata continues to be optimized. Forty-three patients with intractable knee pain were studied prospectively. Consideration for this procedure requires pain of at least a 1-year duration, failure of conservative management, pain localization at a Tinel's point, and at least a 5-point reduction of pain on a visual analog scale after nerve blockade with 1% lidocaine. Thirty patients met the criteria for the procedure and 25 patients underwent the procedure. Mean patient age was 50.3 years and mean duration of pain was 6.6 years. Pain etiology included total knee replacement in 10 patients and trauma in 15 patients. Mean number of prior operations on the knee was 5.1. Sixty-two nerves were excised in the 25 patients, including the infrapatellar branch of the saphenous nerve (N = 24), the tibiofibular branch of the peroneal nerve (N = 5), the medial retinacular nerve (N = 12), the lateral retinacular nerve (N = 8), the medial cutaneous nerve (N = 6), the anterior cutaneous nerve (N = 3), and the lateral femoral cutaneous nerve (N = 4). Complete pain relief was obtained in 11 patients (44%). Partial pain relief was reported in 10 patients (40%). No pain relief was reported in 4 patients (16%). Follow-up ranged from 1 to 4 years. Selective denervation for neuromatous knee pain is beneficial in select patients. Patient satisfaction was 84% (21 of 25 patients) after the procedure. No patient was made worse.

Adult↗
PubMed2001

The topographic relationship between multifocal electroretinographic and behavioral perimetric measures of function in glaucoma.

PURPOSE: To study the spatial relationship between local functional abnormalities found using multifocal electroretinography (MERG) and those measured using standard automated perimetry (SAP) in a group of glaucoma patients with well-defined, localized visual field loss. METHODS: MERG's were measured for 15 patients with longstanding, stable, localized SAP visual field loss and for 27 normal controls using VERIS Science (EDI, San Mateo, CA). Most glaucoma patients had substantial asymmetry of visual field defects across the horizontal midline so that within-eye comparisons of MERG changes could be made in addition to comparisons between glaucoma and healthy, aged-matched controls. RESULTS: For the glaucoma patient group as a whole, conventional measurements of MERG responses, such as peak-to-trough amplitude, peak implicit time, and scalar-product density, did not reveal abnormalities that spatially corresponded to local sensitivity losses determined by SAP visual field thresholds. Some of the patients had MERG abnormalities (e.g., reduced amplitudes) in areas of advanced SAP visual field loss that indicated local retinal dysfunction. On average, glaucoma patients were missing a MERG component that resembled the optic nerve head component as described by Sutter and Bearse. CONCLUSIONS: Different MERG components may be affected at different stages of glaucoma, perhaps reflecting a diversity of pathophysiologic mechanisms. This may complicate spatial and temporal relationships between abnormalities found using the MERG and behavioral perimetry, particularly when conventional measurements of MERG responses are used to characterize a diverse patient group/disease.

Adult↗
PubMed2001

A comparison of noninvasive objective and subjective measurements of the optical density of human ocular media.

BACKGROUND: It is important for both researchers and clinicians to know the spectral composition of the light that reaches the retina. With this in mind, Johnson et al. developed a quick, objective instrument called the Lens Absorption Monitor (LAM) to measure the attenuation of light by the ocular media. Using a more refined method of measuring and correcting for scatter, we compared the results of the LAM against those with a subjective method utilizing a bipartite scotopic brightness-matching procedure (BIP). METHODS: We tested 41 healthy subjects (mean age, 35.9 years) with the LAM and BIP. RESULTS: Intereye correlation coefficients for the LAM were 0.70 at 410 nm and 0.83 at both 430 and 450 nm; for BIP, intereye correlation coefficients were 0.56 at 410 nm, 0.42 at 430 nm, and 0.38 at 450 nm. For optical density as a function of age, there was no statistically significant difference between the two instruments at 410 nm in either the slope (p > 0.43) or y intercept (p > 0.75). However, at both 430 and 450 nm, there was a significant difference in both slope (p < 0.001) and y intercept (p < 0.05) for the two instruments. CONCLUSIONS: With the latest refinements, LAM density measures correlated well with BIP estimates at 410 nm, but not at 430 or 450 nm. This underscores the fact that the LAM measures the spectral density of the anterior segment, whereas the BIP method is a measure of all the ocular media except for macular pigment. The difference between these two measures is consistent with the existence of a prereceptoral, presumably intraretinal, pigment (or pigments) located outside the anatomic fovea that absorbs light at short wavelengths.

Accommodation, Ocular↗
PubMed2001

Senescent changes of the normal visual field: an age-old problem.

PURPOSE: To examine the effect of normal aging on visual field sensitivity and identify the best-fitting function for normal populations. METHODS: Full Threshold standard automated perimetry data (program 24-2, Humphrey Field Analyzer) was collated retrospectively from clinically normal subjects who had previously been recruited for studies of normal visual function. One eye of each subject was randomly selected for analysis. Linear, bilinear, and simple nonlinear candidate functions of mean sensitivity vs. age (independent variable) were applied to these cross-sectional population data. Differences in the aging effect by eccentricity and hemifield were also considered. RESULTS: Data from 562 normal eyes were available for analysis. A significant negative relationship existed between age and mean visual field sensitivity within the cross-sectional population data. Coefficients of determination for the linear, bilinear, and nonlinear functions were 0.21, 0.20, and 0.26, respectively, indicating that the nonlinear function provided best characterization of the effect of age on mean sensitivity. A small but significant increase in the aging effect was present both peripherally (p < 0.001) and superiorly (p < 0.001). DISCUSSION: The nonlinear function that provided the best fit to cross-sectional population data indicates that age exerts an increasing effect on perimetric sensitivity with age, which has implications for clinical devices that use linear age coefficients to correct for normal aging effects. A linear age correction will overestimate aging changes for younger subjects and, therefore, may miss early pathologic changes in visual sensitivity. Conversely, linear age correction will also underestimate aging changes for older subjects and, thus, may overcall pathological sensitivity loss in this group. The effect of age within subjects requires further investigation to provide reliable estimates of the effect of age on sensitivity.

Adolescent↗
PubMed2001

Functional assessment of glaucoma.

Several studies have correlated the location of visual field defect on some of these newer tests to location of optic nerve damage with good results. In addition, there is an important and direct relationship between the psychophysical measures of visual function and location of damage. When a given individual had vision loss on more than one test, the same area of the visual field is affected. In addition, as soon as a repeatable defect is identified on perimetry, progression of the defect on later fields occurs within or adjacent to the initially identified area. These findings have significant implications for the care and follow-up of patients with glaucoma. Using these more sensitive tests has improved greatly our detection of early glaucomatous damage. Follow-up testing that concentrates the evaluation to areas already damaged should improve greatly our ability to identify true change from the significant physiologic variability present in glaucoma.

Glaucoma↗
PubMed2001

DNA methylation is linked to deacetylation of histone H3, but not H4, on the imprinted genes Snrpn and U2af1-rs1.

The relationship between DNA methylation and histone acetylation at the imprinted mouse genes U2af1-rs1 and Snrpn is explored by chromatin immunoprecipitation (ChIP) and resolution of parental alleles using single-strand conformational polymorphisms. The U2af1-rs1 gene lies within a differentially methylated region (DMR), while Snrpn has a 5' DMR (DMR1) with sequences homologous to the imprinting control center of the Prader-Willi/Angelman region. For both DMR1 of Snrpn and the 5' untranslated region (5'-UTR) and 3'-UTR of U2af1-rs1, the methylated and nonexpressed maternal allele was underacetylated, relative to the paternal allele, at all H3 lysines tested (K14, K9, and K18). For H4, underacetylation of the maternal allele was exclusively (U2af1-rs1) or predominantly (Snrpn) at lysine 5. Essentially the same patterns of differential acetylation were found in embryonic stem (ES) cells, embryo fibroblasts, and adult liver from F1 mice and in ES cells from mice that were dipaternal or dimaternal for U2af1-rs1. In contrast, in a region within Snrpn that has biallelic methylation in the cells and tissues analyzed, the paternal (expressed) allele showed relatively increased acetylation of H4 but not of H3. The methyl-CpG-binding-domain (MBD) protein MeCP2 was found, by ChIP, to be associated exclusively with the maternal U2af1-rs1 allele. To ask whether DNA methylation is associated with histone deacetylation, we produced mice with transgene-induced methylation at the paternal allele of U2af1-rs1. In these mice, H3 was underacetylated across both the parental U2af1-rs1 alleles whereas H4 acetylation was unaltered. Collectively, these data are consistent with the hypothesis that CpG methylation leads to deacetylation of histone H3, but not H4, through a process that involves selective binding of MBD proteins.

Acetylation↗
PubMed2001

Daily treatment of horses with equine somatotropin from 4 to 16 months of age.

Fourteen foals between 4 and 4.5 mo of age were used to determine the effects of 12 mo of daily treatment with equine somatotropin (eST) on growth, metabolic, and hormonal characteristics. The foals were paired by sex, type, and lineage, and one of each pair was administered eST daily at 20 microg/kg of BW. Body weights, body measurements, and assessments of glucose tolerance and feedback effects on endogenous somatotropin (ST) secretion were made routinely. Treatment with eST did not alter (P > 0.10) BW, height at withers, length of body, widths of chest and rump, heart girth, length of head, front or rear cannon lengths, front or rear cannon circumferences, gaskin circumference, or skin thickness, even though plasma IGF-I concentrations were doubled (P = 0.012). Glucose concentrations were higher (P = 0.03) in treated horses before glucose infusion; there was no difference (P > 0.10) in the glucose response to infusion. The insulin response to glucose infusion in the treated horses was generally higher (P = 0.0069) than in controls. Endogenous ST secretion in response to a ST secretagogue was reduced (P = 0.0001) in foals treated with eST in all months. The prolactin and thyroid-stimulating hormone responses to thyrotropin-releasing hormone on June 1 were not affected (P > 0.10) by treatment. In conclusion, daily treatment of growing horses with eST for 12 mo at the recommended dose altered the hormonal and metabolic characteristics known to be affected by ST but did not alter the growth characteristics of the animals.

Animals↗
PubMed2001

Primary hyperparathyroidism: what every orthopedic surgeon should know.

The diagnosis of hyperparathyroidism should rarely by missed by the orthopedic surgeon. When a patient presents with a pathologic fracture, routine serum calcium should be obtained. If there is evidence of elevated serum calcium or any of the pathognomonic findings of primary hyperparathyroidism on plain radiographs, total and ionized calcium and an intact parathyroid hormone levels should be obtained to make the diagnosis (Figure 5). When patients require surgical treatment for an orthopedic condition and also need surgery for hyperparathyroidism, the procedures can be safely performed simultaneously. Simultaneous parathyroidectomy corrects the underlying endocrinopathy, thereby improving the outcome of the orthopedic procedure. In addition, these procedures can easily be performed simultaneously under one anesthetic and thereby minimize cost and length of hospitalization.

Aged↗