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Biomedical subjects

R S Baker

Publications and source records attributed to R S Baker.

At least 37 records · Page 2Linked to original sources
PubMed1998

Efficacy of gold weight implants in facial nerve palsy: quantitative alterations in blinking.

Deficient eyelid closure is a major visual threat to patients with unresolved facial nerve palsy. Gold weight implants assisted eyelid closure in patients with paresis of the orbicularis oculi, ameliorating patient complaints of dry eye, excessive tearing, and corneal epithelial breakdown. We used dynamic measures to assess the efficacy of upper eyelid gold weight implantation surgery for facial nerve palsy. The search coil technique was used to record spontaneous blinks bilaterally in six patients, before and after unilateral gold weight implantations into the upper eyelid in severe facial nerve palsy. In uncomplicated facial nerve palsy, the amplitude of blink down-phases for the paretic eyelid was 28.6 +/- 5.7% of the amplitude of the contralateral, normal eyelid. Following corrective surgery, closure of the paretic eyelid improved to 42.6 +/- 7.5% (P < 0.05). There was not a commensurate increase in the peak velocity of blink down-phases, suggesting that gold weight effects are mediated by a passive improvement in blink dynamics.

Adult↗
PubMed1998

Demographic and clinical characteristics of patients with diabetes presenting to an urban public hospital ophthalmology clinic.

OBJECTIVE: This study aims to describe the clinical and sociodemographic characteristics of patients with diabetes who are newly presenting to an inner city public hospital eye clinic. This study also aims to determine the prevalence and severity of ocular morbidity in this population at time presentation and to assess the adequacy of the ophthalmic surveillance to which this population was exposed before presentation. DESIGN: A clinic-based, cross-sectional study. PARTICIPANTS: A total of 118 consecutive patients with diabetes participated. METHOD: During a 2-month interval, all patients with diabetes newly presenting to the Los Angeles County King-Drew Medical Center eye clinic were recruited who were at risk for diabetic eye complications according to American Diabetes Association criteria. Each patient underwent a standardized interviewer-administered questionnaire and a comprehensive ophthalmic examination. RESULTS: Of the 118 patients, 65 (55%) were Hispanic and 51 (43%) were African American. Forty-six percent had a grade school education or less, 91% were unemployed, and 64% had no health insurance. Type two diabetes was predominant (91%), including 24 (22%) of new onset. Thirty-six patients with diabetes (31%) reported duration of diabetes greater than 10 years at time of presentation. At time of presentation, 62% had clinically apparent ophthalmic disease, whereas 40% had advanced ocular disease, including 6.8% of the sample that were legally blind. Sixty-nine patients (58.5%) reported never having had a dilated fundus examination, whereas 31 (63%) of the 49 patients reporting a previous dilated examination were last examined more than 2 years before presentation. Timing of ophthalmic examination was classified as appropriate for 38 patients (32%), marginal for 20 patients (17%), and inappropriate for 60 patients (51%). CONCLUSION: In the setting of an inner city county hospital eye clinic, where the patient population is predominately minority and of low socioeconomic status, ophthalmic surveillance of high-risk patients with diabetes is inadequate and advanced disease often is present at initial presentation. Strategies must be developed to increase the routine use of eye services within this population.

Adult↗
PubMed1998

Pseudotumor of the orbit in early childhood.

Orbital pseudotumor, also known as idiopathic orbital inflammation, is defined as a nonspecific, nonneoplastic inflammatory process of the orbit without identifiable local or systemic causes. The disorder, first described by Birch-Hirschfield in 1905, is more prevalent in the adult population than in the pediatric population. In our study we discuss two cases of pseudotumor of the orbit in children less than 18 months old. This report will highlight the evaluation and management of pediatric orbital pseudotumor and the importance of its inclusion in the differential diagnosis of orbital disorders in young children.

Anti-Inflammatory Agents↗
PubMed1998

Correlates of recency of eye examination among elderly African-Americans.

This study uses a theoretical model of health services utilization to assess the effects of predisposing, enabling, and need-for-care characteristics on recency of eye examinations among a sample of 998 elderly African-American persons. More than 64% of participants reported that they had had eye examinations within the last 12 months. Multiple logistics regression analysis explains 13.3% of the variance of eye examinations. This data indicates that recency of eye examination is related to health locus of control, private insurance, Medicare, insulin-dependent diabetes, and presence of eye disease. No significant relationship between recency of eye examination and self-rated health status, social support, vision impairment, and non-insulin-dependent diabetes were detected. The lack of association between non-insulin-dependent diabetes and the recency of eye examination suggests that the amount of preventive care in place may not be adequate. This data shows that the unique contributions of need characteristics account for a major variance of recency of eye examination. However, enabling characteristics play a significant role in sending the participants of this study to eye-specialists, even after need-for-care factors are held constant.

Black or African American↗
PubMed1998

Emergency department utilization, hospital admissions, and physician visits among elderly African American persons.

This study uses a theoretical model of health services utilization to examine (a) emergency department utilization, (b) hospital admissions, and (c) office-based physician visits among a sample of 998 low-income elderly African American persons. Poisson Regression analysis was used to estimate the parameters specified in the Andersen behavioral model. Some of the more interesting results include the following: (a) a greater frequency of emergency room visits among respondents with a lower level of accessibility to physician services, (b) a lack of a significant relationship between some chronic illnesses such as diabetes and heart problems and the frequency of office-based physician visits, (c) a greater number of hospital admissions among insured persons, and (d) a significant impact of the health locus of control indexes on all three types of health care utilization. The results of this study challenge the assumption that hospital and emergency use are the results of nondiscretionary behavior.

Black or African American↗
PubMed1997

Absence of oculomotor and trochlear motoneurons leads to altered extraocular muscle development in the Wnt-1 null mutant mouse.

Wnt-1 null mutant mice lack midbrain somatic motor nuclei. Primordial migration and spatial patterning of the extraocular muscles, however, was preserved, but myogenesis was disrupted in aneural muscles. Some muscles normally innervated by oculomotor and trochlear nuclei received aberrant innervation, which proved sufficient to maintain prenatal stages of myogenesis. The absence of motoneurons followed by innervation from inappropriate motoneuron pools is a viable candidate mechanism in ocular motility disorders, including Duane retraction syndrome and congenital fibrosis of extraocular muscle.

Alleles↗
PubMed1997

The role of blink adaptation in the pathophysiology of benign essential blepharospasm.

OBJECTIVE: To investigate eyelid movements in patients with benign essential blepharospasm (BEB), with an emphasis on the characterization of the kinematics of normal and spastic blinks, assessment of interocular differences, and further delineation of the role of adaptive blink mechanisms in eyelid movement disorders. PATIENTS AND METHODS: The electromagnetic search coil technique was used to record the metrics of blinks bilaterally in 5 patients with untreated BEB. Eyelid kinematics and the main-sequence (peak velocity vs amplitude) relationships were analyzed. RESULTS: Patients with BEB exhibited a decrease in blink amplitude and peak velocity. Moreover, the main-sequence slope was decreased bilaterally. Spasms were bilateral and relatively conjugate. There was no change in the coordination of normal blinking across the 2 eyelids. CONCLUSIONS: These data demonstrate the operation of the adaptive regulation of blinking in an eyelid movement disorder. The findings suggest that the adaptive regulation of blink is a bilateral event. Blink-adaptive control systems can act on the blink reflex excitability and main-sequence relationships, changing these either together or independently. The hyperexcitable blink reflex of BEB is met by what is believed to be an adaptive decrease in the main-sequence slope that would decrease the strength of debilitating spasms. Collectively, these data extend the knowledge of the pathophysiology of BEB and, perhaps more important, establish the role of blink system plasticity in eyelid movement disorders.

Adaptation, Physiological↗
PubMed1997

Estrogen-induced increases in coronary blood flow are antagonized by inhibitors of nitric oxide synthesis.

OBJECTIVE: Estrogen receptors have been found in coronary arterial endothelial and vascular smooth muscle cells. Therefore the present study was designed to determine if estradiol-17 beta can increase coronary blood flow and if so whether the changes are mediated by nitric oxide. STUDY DESIGN: Five oophorectomized non-pregnant sheep were chronically instrumented to measure blood pressure, heart rate, cardiac output, left circumflex coronary blood flow and central venous pressure. Animals received estradiol-17 beta (1.0 micrograms/kg) and cardiovascular responses were followed for 135 min. RESULTS: Estradiol-17 beta (1.0 micrograms/kg) increased left circumflex (coronary) blood flow 28 +/- 3%, cardiac output 15 +/- 1% and heart rate by 13 +/- 3%. Coronary vascular resistance decreased 23 +/- 5%, systemic vascular resistance decreased by 12 +/- 2% while blood pressure did not change significantly. Administration of the nitric oxide synthetase inhibitor L-nitroarginine methylester (L-NAME), had no effect on basal coronary blood flow but completely reversed estradiol-17 beta induced increases in coronary blood flow. CONCLUSION: These results demonstrate that estrogen increases coronary blood flow in the non-pregnant sheep and that L-NAME, an inhibitor of nitric oxide, is able to reverse the estrogen induced flow changes.

Animals↗
PubMed1997

Teleophthalmology: rationale, current issues, future directions.

Relatively little information exists concerning the delivery of ophthalmic services via telemedicine, yet ophthalmology is particularly amenable to the utilization of such applications. This paper discusses the technological issues pertinent to the research, development, and assessment of teleophthalmology delivery systems and begins to define the parameters that will determine the sustainability of teleophthalmology. A prototype urban teleophthalmology delivery system is presented in the context of improving access to eye care for an underserved inner-city population. Potential enhancements to the prototype telephthalmology system are discussed.

Adolescent↗
PubMed1997

Effects of continuous infusion of endothelin-1 in pregnant sheep.

Plasma concentration of endothelin-1, a potent vasoconstrictor produced by the vascular endothelium, has been observed to be significantly increased in a number of pathophysiological states, including preeclampsia. In the present study we have evaluated the effects of elevated plasma endothelin-1 in pregnant sheep by continuous exogenous endothelin-1 administration. Nine pregnant ewes (110+/-5 days' gestation) were instrumented for measurements of maternal mean arterial pressure, renal blood flow, and uterine blood flow. After recovery, endothelin-1 was infused intravenously for 4 hours at a dose that was adjusted to raise mean arterial pressure by approximately 20 mm Hg by the end of the first hour (range 5 to 20 ng/kg per minute). Mean arterial pressure, renal blood flow, uterine blood flow, urinary protein excretion, hematocrit, and plasma endothelin-1 concentration were measured hourly, and renal and uterine vascular resistances were calculated. Endothelin-1 produced significant increases (% change from baseline at t=4 hours) in mean arterial pressure (45+/-8%), renal vascular resistance (353+/-66 %), and uterine vascular resistance (59+/-21%). Endothelin-1 also increased microvascular permeability both systemically and within the kidney, as suggested by marked increases in hematocrit (0.27+/-0.01 to 0.32+/-0.01) and urinary protein concentration (0.95+/-0.1 to 7.9+/-3.2 mg/mL per mg creatinine). There was a highly significant correlation (P<.0001) between plasma endothelin-1 and mean arterial pressure, renal vascular resistance, uterine vascular resistance, hematocrit, and urinary protein content in all sheep studied. In addition, plasma endothelin-1 corresponded well with the time course of the changes in cardiovascular parameters and urinary protein excretion observed. These results provide evidence to suggest that elevation of circulating endothelin-1 in pregnant sheep can produce cardiovascular and hemodynamic changes that in many ways resemble the human disease preeclampsia. This supports the hypothesis that endothelial cell damage and/or dysfunction that is associated with increased production of endothelin-1 could directly contribute to the progression of preeclampsia.

Animals↗
PubMed1997

Maladaptive neural compensatory mechanisms in Bell's palsy-induced blepharospasm.

We described four patients with Bell's palsy and blepharospasm and evaluated potential mechanisms that may be responsible for an apparent association between the two disorders. Eyelid movements in spontaneous blinks were studied by the search coil technique in patients with this novel disorder. Kinematic analyses documented bilateral eyelid spasm subsequent to unilateral Bell's palsy. The temporal interval between the onset of palsy and onset of blepharospasm was highly variable (weeks to > 20 years). Changes in the relationship between spontaneous blink peak velocity and amplitude, the main sequence, shared features previously found in uncomplicated Bell's palsy and blepharospasm patients. Furthermore, as in patients with typical Bell's palsy and idiopathic blepharospasm, both normal blinks and spasms were conjugate in spite of interocular differences in blink amplitude/peak velocity. We suggest that there is a correlation between the eyelid palsy and subsequent blepharospasm, and have designated this potentially new disease entity as Bell's palsy-induced blepharospasm. We propose a two-stage model for Bell's palsy-induced blepharospasm in which blink adaptive systems may produce the maladaptive consequence of eyelid spasms.

Adult↗
PubMed1997

Age-related changes in human blinks. Passive and active changes in eyelid kinematics.

PURPOSE: The authors analyzed eyelid kinematics in normal aging subjects to test the hypothesis that eyelid movements exhibit age-related changes and that blink disorders prevalent among the elderly, in turn, represent an outcome of normal aging processes. METHODS: The electromagnetic search coil technique was used to study blinks in normal human subjects for each decade from 40 to 89 years. Blink metrics (amplitude, peak velocity, and duration), main sequence relationships, and conjugacy were assessed. RESULTS: Mean amplitude and peak velocity of blinks decreased with age for spontaneous blinks and, to a lesser extent, for voluntary blinks. Some but not all, of this decline could be attributed to a peripheral phenomenon, narrowed palpebral fissure width. The spontaneous blink down phase main sequence slope also declined with age. By contrast, blink rate and the coordination of movements of the two eyelids--blink conjugacy--exhibited no change. CONCLUSIONS: These data demonstrate that disorders of blink systems typically seen in persons 50 years of age or older occur on a background of normal age-dependent changes in eyelid kinematics. Alterations in main sequence slope imply the operation of central adaptive systems during aging. Reduction in main sequence slope is interpreted as a reduction in aggregate orbicularis oculi motoneuron activity. Such a central neurologic adjustment in the motor output of blink systems may serve to compensate for an age-related increase in blink reflex excitability. Compensatory reduction in the main sequence relationship may offset a potentially hyperexcitable blink reflex, thereby reducing the likelihood of disorders such as blepharospasm. The authors conclude that although there are changes in the kinematics of blinking with age, such changes do not necessarily predispose an aging population to eyelid motility disorders.

Adult↗
PubMed1996

Bell's Palsy-associated blepharospasm relieved by aiding eyelid closure.

The efficacy of the blink reflex is maintained by adaptive control mechanisms. We describe a 39-year-old woman with the rare complication of blepharospasm-like symptoms appearing contralateral to an eyelid weakened by facial nerve palsy. The hyperexcitable blink reflex may be a maladaptive consequence of adaptive systems but was not accompanied by an expected increase in main sequence slope. Eyelid spasms were eliminated by the implantation of a gold weight to assist closure of the paretic eyelid. We suggest that aiding closure of the weak eyelid in this case caused a reduction in blink system excitability via the same compensatory mechanisms that initially produced the eyelid spasm. Data also suggest that blink-adaptive systems act via changes in reflex excitability and/or main sequence relationships, and that these may be regulated either synergistically or independent of one another.

Adult↗
PubMed1996

Corneoscleral laceration caused by air-bag trauma.

PURPOSE: To report a case of a corneoscleral laceration sustained as a direct result of inflation of a driver-side air bag. METHODS: A patient who sustained a severe ocular injury in a low-speed motor vehicle accident underwent clinical and radiologic examination and subsequent treatment. RESULTS: The left eye underwent primary repair of a complex corneoscleral laceration. Two weeks postoperatively, visual acuity in the left eye remained at bare hand motion. CONCLUSION: Although air-bag-related eye trauma may be relatively infrequent, the severity of the injuries incurred warrant research efforts to explore new air-bag designs that minimize the risk of ocular injury.

Accidents, Traffic↗
PubMed1996

Demographic factors in a population-based survey of hospitalized, work-related, ocular injury.

PURPOSE: To obtain population-based estimates of the incidence of severe work-related ocular trauma and to identify demographic factors related to increased risk of this type of injury. METHODS: A statewide population-based survey of severe work-related ocular injury was performed using hospital discharge data. These data were derived from all inpatient admissions to nonfederal, acute-care hospital facilities in the state of California during 1988. Worker's compensation was used as the principal payor code to establish the work-relatedness of a given ocular injury. Census data for the state of California were used to obtain population denominators. RESULTS: Two hundred sixty-nine (approximately 14.3%) of all admissions for which ocular trauma was the principal diagnosis (1,876) were work related. Annual incidence for severe work-related ocular injury was 1.76 per 100,000 employed persons when ocular trauma was the principal diagnosis and 2.98 per 100,000 employed persons when ocular trauma was a principal or secondary diagnosis. Projected to the working-age United States population (128 million) these annual rates correspond to an estimated 2,165 acute hospitalizations for work-related ocular trauma as the principal diagnosis, and an estimated 3,745 acute hospitalizations for work-related ocular trauma as a principal or secondary diagnosis. Incidence of severe work-related ocular injury was highest among men, Hispanics, and individuals 20 to 24 years of age (5.02, 3.72, and 4.64 per 100,000 employed per year, respectively). CONCLUSIONS: The workplace accounts for a substantial proportion of severe ocular injury. Demographic groups at highest risk for this type of injury are men, Hispanics, and young adults.

Accidents, Occupational↗
PubMed1996

Muscles of a different 'color': the unusual properties of the extraocular muscles may predispose or protect them in neurogenic and myogenic disease.

The rules that govern many aspects of skeletal muscle structure and function are very different for the extraocular muscle allotype. The myoblast lineages present in the extraocular muscle primordia are permissive for generation of an unusually wide range of fiber types. The balance that is struck between genetic specification and activity dependent factors in shaping fiber phenotype to suit the demands of complex visuomotor systems is not yet well defined. Because skeletal muscle has high energy demands, diversity in fiber types is needed to maximize efficiency; greater diversity in fiber composition then indicates a more diverse functional repertoire. Together, the characteristics of small motor unit size, precise dependence of muscle force upon motor neuron discharge rate, high contractile speed but low tension development, and contractile protein heterogeneity contribute toward the high precision and diversity that is required for eye movements. Finally, the structural and functional characteristics and plasticity of the individual extraocular muscle fiber types play an important role in determining their response to disease or manipulation. The lack of uniform responses across the muscle allotypes in disease, or in response to pharmaceutical or surgical interventions, requires that we obtain a better understanding of the fundamental differences that exist between muscle groups.

Humans↗