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Biomedical subjects

M A Chang

Publications and source records attributed to M A Chang.

12 recordsLinked to original sources
PubMed2005

A comparison of the potential acuity meter (PAM) and the illuminated near card (INC) in patients undergoing phacoemulsification.

PURPOSE: To compare the accuracy of the potential acuity meter (PAM) and the illuminated near card (INC) in patients undergoing phacoemulsification. METHODS: During presurgical evaluations, both PAM and INC were tested on each study patient following dilation. Patients then rated the subjective ease of use of each test. Best spectacle-corrected visual acuity (BSCVA) was recorded at 4 and 12 weeks postoperatively. McNemar's chi(2) test for paired associations was used to analyse categorical data; paired t-tests were used for continuous variables. RESULTS: Overall, the INC was more likely than the PAM to predict BSCVA within one Snellen line (P=0.002), but this difference decreased for accuracy within two lines. The PAM predicted BSCVA within one line in 87 (70.7%) eyes, as compared to 102 (82.9%) eyes by the INC. The PAM was accurate within two lines in 109 (88.6%) eyes; the INC was accurate in 115 (93.5%) eyes. The PAM was more likely to underpredict potential acuity (P<0.001), while the INC was more likely to overpredict (P=0.004) or give exact predictions of BSCVA (P<0.001). Accuracy of the INC declined in eyes with macular comorbidity. The PAM and INC were rated as 'easy' tests by 54 (45.4%) and 93 (78.2%) patients, respectively. CONCLUSIONS: Both the PAM and the INC were useful for predicting BSCVA after phacoemulsification, but the PAM was more likely to underestimate potential acuity. The INC was easier for patients to use, and had better accuracy than the PAM in patients without macular comorbidity, but was more likely to overestimate potential acuity.

Adolescent↗
PubMed2003

Occupational risk for nephrolithiasis and bladder dysfunction in a chauffeur.

The occupational risks for nephrolithiasis have not been widely studied. The published literature focuses on exposure to heat stress and toxic substances, not on the equally important behavioral risk factor of limited water consumption over many years. Urologic morbidity has been associated with suppressing the need to drink or void under restrictive work environments; however, no such studies link work related behavioral change with the development of kidney stones. This case report is the first to associate a restrictive work environment with limited fluid consumption, resulting in the development of nephrolithiasis.

Automobile Driving↗
PubMed2000

Biphasic ocular inflammatory response to endotoxin-induced uveitis in the mouse.

OBJECTIVE: To examine the kinetics and mechanisms of endotoxin-induced uveitis in the mouse. METHODS: C3H/HeN mice were injected subcutaneously with 0.3 mg of Salmonella typhimurium lipopolysaccharide (LPS) in 0.1 mL of phosphate-buffered saline solution or phosphate-buffered saline solution alone in 3 separate experiments; mice were killed after 1, 3, 5, and 7 days. In 2 other separate experiments, mice were killed 1, 3, 6, and 24 hours after LPS injection. All eyes were collected for histological examination, immunohistochemical analyses, aqueous protein level determination, and reverse transcriptase-polymerase chain reaction for ocular interleukin (IL)1alpha, IL-6, tumor necrosis factor alpha, and granulocyte-macrophage colony-stimulating factor messenger RNA (mRNA). Enzyme-linked immunosorbent assay was used to measure tumor necrosis factor alpha and IL-6 levels in aqueous and serum samples. RESULTS: Results were consistent for all experiments. Numbers of ocular inflammatory cells and levels of aqueous protein peaked 1 and 5 days after LPS injection. Control mice did not develop inflammation. Serum and aqueous IL-6 and ocular IL-6 mRNA levels peaked at 1 day and subsided at 3 days. However, ocular IL-1alpha, tumor necrosis factor alpha, and granulocyte-macrophage colony-stimulating factor mRNA appeared, peaked, and subsided at 3, 5, and 7 days, respectively. Predominant infiltrating cells were neutrophils at 1 day and macrophages at 5 days. Although no ocular inflammatory cells were detected before 24 hours after LPS injection, tumor necrosis factor alpha mRNA was noticed at 1 hour, peaked at 3 hours, and disappeared at 6 hours and granulocyte-macrophage colony-stimulating factor mRNA was spotted only at 3 hours after LPS injection. CONCLUSIONS: The ocular inflammatory response to C3H/ HeN mouse endotoxin-induced uveitis is biphasic for 7 days. The first wave appears at day 1 and subsides by day 3. A second, higher peak appears at day 5. The 2 inflammatory waves are related to the kinetics of the different cytokines released in the eye. This is in contrast to the rat monophasic endotoxin-induced uveitis model, which has only one peak of intense inflammation associated with cytokine release. CLINICAL RELEVANCE: A biphasic inflammatory response associated with cytokine release lasting several days is observed in C3H/HeN mice with endotoxin-induced uveitis. Because human anterior uveitis has a tendency to be recurrent in nature, this might be a better experimental model.

Animals↗
PubMed2000

Tetracycline-inducible system for photoreceptor-specific gene expression.

PURPOSE: To develop a system for inducible photoreceptor-specific gene expression in transgenic mice. The tetracycline regulatory system was chosen because it possesses the useful property of direct control of gene expression through use of an exogenous agent, doxycycline, a tetracycline derivative. METHODS: Transgenic mice were generated that carried the reverse tetracycline-controlled transactivator under the control of the photoreceptor-specific promoters for rhodopsin and interphotoreceptor retinoid-binding protein. These animals were crossed with transgenic mice carrying the lacZ reporter gene under control of the tetracycline operator cassette, creating doubly transgenic mice. Doxycycline was administered to induce expression of the reporter gene. Reporter assays were then performed to evaluate lacZ expression. RESULTS: Doxycycline administration led to photoreceptor-specific expression of the lacZ reporter gene in the doubly transgenic mice. X-gal staining was restricted to photoreceptor inner segments and synaptic termini. Induction could be achieved by addition of the drug to the animals' drinking water or by intravitreal injection. Induction was noted within 24 hours of doxcycline administration. Because of variability among animals, there was an approximate correlation, but not a clean dose-response curve relating drug dose to level of reporter expression. CONCLUSIONS: A transgenic system for inducible photoreceptor-specific gene expression has been developed. This system is currently being exploited to study the effects of regulated expression of genes of biological interest.

Animals↗
PubMed1998

Transcriptional regulation of cellular retinaldehyde-binding protein in the retinal pigment epithelium. A role for the photoreceptor consensus element.

Cellular retinaldehyde-binding protein (CRALBP) is abundantly expressed in the retinal pigment epithelium (RPE) and Muller cells of the retina, where it is thought to function in retinoid metabolism and visual pigment regeneration. Mutations in human CRALBP that destroy retinoid binding have been linked to autosomal recessive retinitis pigmentosa. To identify the DNA elements that regulate expression of the human CRALBP gene in the RPE, transient transfection studies were carried out with three CRALBP-expressing human RPE cell culture systems. The regions from -2089 to -1539 base pairs and from -243 to +80 base pairs demonstrated positive regulatory activity. Similar activity was not observed with cultured human breast, liver, or skin cells. Since sequence analysis of the -243 to +80 region identified the presence of two photoreceptor consensus element-1 (PCE-1) sites, elements that have been implicated in photoreceptor gene regulation, the role of these sequences in RPE expression was examined. Mutation of either PCE-1 site significantly reduced reporter activity, and mutation or deletion of both sites dramatically reduced activity. Electrophoretic mobility shift analysis with RPE nuclear extracts revealed two complexes that required intact PCE-1 sites. These studies also identified two identical sequences (GCAGGA) flanking PCE-1, termed the binding CRALBP element (BCE), that are also important for complex formation. Southwestern analysis with PCE-1/BCEcontaining probes identified species with apparent masses near 90-100 and 31 kDa. These results begin to identify the regulatory regions required for RPE expression of CRALBP and suggest that PCE-1-binding factor(s) may play a role in regulating RPE as well as photoreceptor gene expression.

Carrier Proteins↗
PubMed1992

Pulse oximetry and peak flow as indicators of wheezing severity in children and improvement following bronchodilator treatments.

This study examined the changes from the initial peak flows and oxygen saturations (OSAT) of wheezing children at presentation to the emergency department through their treatment in the emergency department. Data was collected prospectively on 785 patients 5 to 20 years of age during an 11-month period from November 1, 1990, to September 30, 1991. Both the initial OSAT and peak flows were correlated with the number of bronchodilator treatments required in the emergency department and with the need for hospitalization. Both the initial OSAT and the peak flows had a limited ability to predict the need for hospitalization. Oxygen saturation appears to be a valid measure of wheezing severity and is more easily obtained in children of all ages. Following bronchodilator treatment, peak flow results in a larger quantitative improvement than OSAT; however, this difference does not appear to have any significant advantage. Aerosolized albuterol and subcutaneous epinephrine resulted in a similar degree of improvement as measured by peak flow and by oxygen saturation, with clinically similar changes in heart rate.

Adolescent↗
PubMed1990

Surgical goniosynechialysis for angle-closure glaucoma.

Fifteen patients with synechial angle-closure glaucoma uncontrolled by medical and laser therapy were treated with surgical goniosynechialysis. Five patients were treated with goniosynechialysis alone, and ten were treated with goniosynechialysis in combination with other surgical procedures. The procedure was successful, in terms of reducing synechiae, in 14 eyes (93%). The extent of angle closure was reduced from 340 degrees +/- 45 degrees (mean +/- standard deviation) preoperatively to 80 degrees +/- 70 degrees postoperatively; the mean reduction was 260 degrees +/- 95 degrees (P less than 0.0001) for the group overall and 280 degrees +/- 80 degrees (P less than 0.0007) for the subgroup treated with goniosynechialysis alone. The mean preoperative intraocular pressure (IOP) was 40 +/- 4 mmHg. The mean postoperative IOP was 14 +/- 4 mmHg. The mean reduction in IOP was 26 +/- 15 mmHg (P less than 0.0001) for the group overall and 27 +/- 18 mmHg (P less than 0.015) for the subgroup treated with goniosynechialysis alone. Glaucoma medications were reduced from a mean of 2.6 +/- 1.0 preoperatively to 1.1 +/- 1.2 postoperatively for the group overall and to 1.4 +/- 1.5 for the subgroup treated with goniosynechialysis alone. Complications consisted of two eyes with intraoperative bleeding. One of these required intraoperative conversion to surgical trabeculectomy. The other was associated with a transient postoperative IOP elevation to 40 mmHg. Surgical goniosynechialysis may be an effective means of reducing synechiae and lowering IOP, either alone or in conjunction with other surgical procedures, in patients with angle closures of less than 6 months' duration.

Adult↗
PubMed1987

The Amsler grid.

Explore the source record for details and available documents.

Humans↗
PubMed1986

Ocular abnormalities associated with cutaneous melanoma and vitiligolike leukoderma.

Several varieties of ocular pathology are associated with acquired cutaneous hypomelanosis (leukoderma; vitiligo). Our current study was undertaken to investigate the relationship between ophthalmologic disorders and a specific depigmentary phenomenon, the vitiligolike leukoderma of cutaneous melanoma. Over the past 14 years, eight patients with cutaneous melanoma and widespread areas of hypopigmentation were identified at the Pigmented Lesion Clinic of the Massachusetts General Hospital. The seven patients who underwent ophthalmologic examination had pigment-related ocular abnormalities. Among these were inflammations of the uveal tract in three patients, heterochromia in two, halo nevi of the choroid in one, and hypopigmentation and/or atrophy of the retinal pigment epithelium or choroid in four. Our findings demonstrate that ocular disease may be a component in a syndrome consisting also of cutaneous melanoma and vitiligolike leukoderma and suggest the need for complete ophthalmologic examinations in patients with melanoma and leukoderma.

Adult↗
PubMed1985

The dysplastic nevus syndrome. A pedigree with primary malignant melanomas of the choroid and skin.

Intraocular and cutaneous melanomas developed in a family with features of the dysplastic nevus syndrome. (The proband had a choroidal melanoma, his son had a cutaneous melanoma, and his grandchildren have mildly atypical melanocytic lesions clinically.) The syndrome is characterized by clinically and histologically atypical nevi, which may serve as cutaneous markers to identify persons at high risk for melanomas, both of the skin and the eye. Although it has been proposed recently that the association of intraocular melanoma with cutaneous melanoma and the dysplastic nevus syndrome may be coincidental, statistical analysis suggests that the occurrence of the two forms of melanoma in the same patient and in different members of the same family is not explained by chance alone. Therefore, until the relationship between intraocular and cutaneous melanomas is more fully elucidated, recognition of the dysplastic nevus syndrome is important, and the skin of patients suspected of having intraocular melanomas should be examined routinely for evidence of atypical melanocytic lesions.

Adolescent↗
PubMed1984

Sample size graphs for "proving the null hypothesis".

Sample size graphs are given for clinical trials designed to test whether an experimental therapy is as effective as a standard therapy. We assume a dichotomous outcome variable and a one-sided test of the hypothesis that the probability of success with standard therapy is greater than the probability of success with experimental therapy by at least some specified amount delta. Graphs are given for significance level alpha = 0.01, 0.025, 0.05; type II error beta = 0.10, 0.20; and delta = 0.10, 0.20.

Clinical Trials as Topic↗