Search PubMed⌕ Search

Biomedical subjects

R G Marks

Publications and source records attributed to R G Marks.

96 records · Page 6Linked to original sources
PubMedDate not supplied

Measuring the correlation between time series of hormonal data.

Several biomedical experiments have as their objective the determination of a relationship between a pair of time series. Often, the investigator wishes to discover if one series has a lagged dependence on the other. The analysis required in such an experiment involves a three step approach utilizing both multiple regression and time series techniques. This paper presents an example of this type of experiment and describes the steps to be followed in analysing the results.

Animals↗
PubMedDate not supplied

Paradigm shifts in clinical trials enabled by information technology.

The use of the world wide web for clinical trials changes the processes of performing clinical research in several fundamental ways. Greatly improved security, monitoring capability, and accuracy and timeliness of study conduct can be achieved while lowering cost. Data quality is enhanced while co-ordinating centre effort is reduced. The web provides a natural environment for linking the various components of clinical research, leading to new levels of simplicity and efficiency. It also enhances opportunities for recruitment of study investigators and patients. Other information technology tools and databases can be used to assist in this regard as well. Web-based trials change the relationship of the investigator site to the study and the site to the co-ordinating centre. Different roles and responsibilities lead to simplified processes and more and higher quality data. Many standard co-ordinating centre activities, such as randomization, protocol implementation and amending, document tracking, adverse event reporting, site monitoring, report generation and data analysis are all fundamentally changed in a web-based trial. Opportunities are enhanced to identify potential investigators and support their successful study conduct. As the role of investigator sites is changed in web-based research, more primary care medical providers can be attracted to research, providing more typical patients to studies than those sometimes available through more traditional research sites, especially those at academic study sites. Other activities can now be co-ordinated electronically with the advent of the web. The Institutional Review Board (IRB) can use online tools to control investigator participation, resulting in improved study efficiency and patient safety. A web-based research pharmacy provides tremendous efficiencies in managing and distributing study medications. Financial payments to the sites can be performed and recorded electronically, or even administered based on timeliness and quality of the data. Our early experience with web-based trials indicates that there can be tremendous gains in study efficiency and accuracy by restructuring processes, roles and responsibilities through a comprehensive centralized, web-based trial. The future appears bright for web-based clinical trials.

Clinical Trials as Topic↗
PubMedDate not supplied

Arcuate transverse keratotomy for astigmatism followed by subsequent radial or transverse keratotomy. ARC-T Study Group. Astigmatism Reduction Clinical Trial.

BACKGROUND: We studied the safety and efficacy of arcuate transverse keratotomy performed for the primary correction of naturally occurring corneal astigmatism. METHODS: A multicenter, prospective evaluation of one-stage arcuate transverse keratotomy was conducted in 160 eyes with 1.00 to 6.00 diopters (D) of naturally occurring astigmatism. Vector analysis was used. After 1 month, those eyes that needed further refractive surgery received radial keratotomy for myopia and second-stage arcuate transverse keratotomy for residual astigmatism. RESULTS: Mean preoperative refractive cylinder was 2.80 D. At 1 month, the vector-corrected change was 2.30 D. Eighty-eight (61%) eyes had at least 1.00 D of residual refractive cylinder and 24 (17%) had at least 2.00 D. Eyes undergoing a second surgery averaged 1.60 D of vector-corrected effect, for a total effect of 2.90 D from both surgeries, indicating the astigmatic refractive effects were not additive. Eyes that had radial keratotomy alone as the second surgery demonstrated a similar change in refractive cylinder as eyes that had both radial and transverse keratotomies. Two eyes lost two lines of spectacle-corrected visual acuity, 29 eyes lost one line, 84 showed no change, and 26 eyes improved one line. CONCLUSION: Arcuate transverse keratotomy reduced refractive astigmatism. Both overcorrection and undercorrection were common. Complications were infrequent but occasionally caused significant irregular astigmatism. Arcuate transverse keratotomy appears to be a safe procedure with few complications.

Adolescent↗
PubMedDate not supplied

Five-year results of radial keratotomy.

We present 5-year findings on 198 consecutive radial keratotomy surgeries. Follow-up was obtained on 134 (68%) of these eyes. Mean spherical equivalent (SE) was -4.3 diopters before surgery, average keratometry was 44.11 D, and 75% of eyes had uncorrected distance acuity of 20/400 or worse. Average SE was -0.52 D for eyes seen at 5 years, which compares with -0.78 D for eyes examined at 18 months. Seventeen percent of eyes show at least a 1-D change in refraction from 18 months to 5 years compared with 13% between 18 months and 3 years. Fifty-six percent of eyes are within 1 D of emmetropia at 5 years, compared with 66% at 18 months. Uncorrected visual acuity was at least 20/40 in 62% of eyes seen at 5 years and in 73% of eyes seen at 18 months. Ten percent of eyes have lost at least two lines of best-corrected visual acuity from before surgery to 5 years later. Factors are identified that relate to loss of uncorrected and best corrected acuity over 5 years. Average keratometry at 5 years is 40.7 D, as compared with 41.2 D at 18 months. Long-term keratometric results appear less stable than refractive results and a theory for this instability is presented. The results indicate radial keratotomy to be safe and effective for the vast majority of patients in this series for 5 years postoperatively.

Adult↗
PubMedDate not supplied

Benzodiazepine use in an ambulatory elderly population: a 14-year overview.

A survey on use of benzodiazepines was conducted among participants in the Florida Geriatric Research Program. In 1978-79, benzodiazepine use was reported by 14.4% of 1448 women and 9.7% of 855 men; in 1984-85, by 12.0% of 1429 women and 5.9% of 784 men; and in 1991-92, by 13.4% of 1124 women and 6.6% of 497 men. The changes were not significant. During this period the mean ages of the women increased from 74.6 to 78.1 years and the men from 75.0 to 80.2 years. Chlordiazepoxide, diazepam, and flurazepam accounted for 98.1% of all benzodiazepines used in 1978-79 and for 35.5% in 1991-92, when alprazolam, lorazepam, and temazepam accounted for 47.1% of benzodiazepines used.

Age Factors↗