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Biomedical subjects

B S Hawkins

Publications and source records attributed to B S Hawkins.

At least 19 recordsLinked to original sources
PubMed1995

Reliability of visual acuity measurements and screening under field conditions.

PURPOSE: The purpose of this analysis was to investigate the reliability of visual acuity screening and measurements made under field conditions when standardization of all test conditions is not possible. SETTING AND METHODS: In the Washington County Follow-Up Eye Study conducted in 1985 among cases of ocular histoplasmosis and controls from the same community who had been selected in 1970, a primary goal was to obtain a current visual acuity measurement of each eye of each participant in order to assess 15-year changes in visual acuity. Both visual acuity screening and measurement were accomplished on two separate occasions and in two separate locations (home or workplace and clinic) for 308 eyes and 317 eyes, respectively, of 161 participants. Screening was used to classify the visual acuity as 20/40 or better, worse than 20/40 but at least 20/160, or worse than 20/160. Screening and measurement were accomplished on at least one occasion for the eyes of 192 of 216 eligible individuals. RESULTS: Among 308 eyes screened twice, 289 (94%) were classified identically (kappa = 0.80). Among 317 eyes with visual acuity measured on two occasions, the measurements were within two lines for 305 eyes (96%; kappa = 0.50). Among eyes for which classifications of visual acuity from screening and measurement could be compared, 325 (96%) of 340 assessed at home and 326 (96%) of 338 assessed in clinic were classified in the same way (kappa = 0.86 and 0.88, respectively). CONCLUSION: Despite the unavoidable lack of standardization of test conditions when visual acuity was screened and measured in the home or work-place, the results were highly reliable when compared with visual acuity testing in the clinic under standard conditions.

Aged↗
PubMed1992

A review of mortality from choroidal melanoma. I. Quality of published reports, 1966 through 1988.

The literature concerning mortality after a diagnosis of choroidal melanoma was reviewed to identify relevant articles published from 1966 through 1988 and to select those with mortality rates presented separately by tumor size for inclusion in a pooled analysis (meta-analysis) of 5-year mortality after enucleation for choroidal melanoma. The quality of the published literature for our purposes was assessed. Candidate articles were identified from a search of the MEDLINE files by an information specialist. Altogether, of 217 candidate articles, 76 (70 from the MEDLINE search and six more from our files) qualified for review. All-cause mortality rates were reported in 80% of the articles. Among six aspects of design and methods for which information was sought, eligibility criteria were reported in 52 (68%) of the 76 articles and statistical methods were cited in 38 (50%); other information was reported with intermediate frequency. Quality scores based on completeness of reporting with respect to 16 factors ranged from 13.3 to 92.3 of a possible 100.0. Findings suggest that researchers, clinicians, journal editors, and reviewers should be more attentive to the completeness of reports from clinical research studies with respect to basic information regarding design and methods.

Choroid Neoplasms↗
PubMed1992

A review of mortality from choroidal melanoma. II. A meta-analysis of 5-year mortality rates following enucleation, 1966 through 1988.

With the use of data published during the period from 1966 through 1988, a pooled analysis (meta-analysis) of 5-year mortality rates among patients who had an eye enucleated for choroidal melanoma was performed to provide a more robust estimate of this rate than could be obtained from any single study. The literature concerning mortality following a diagnosis of choroidal melanoma has been reviewed systematically and described in a separate article. Of 76 reports published from 1966 through 1988, 29 were excluded from the meta-analysis because there were no cases treated by enucleation alone, mortality was not reported by time from enucleation, fewer than 10 cases were reported, or 5-year mortality rates were not reported or derivable from the data presented. Ten additional reports were excluded because they were based on data for the same set of patients as another article in the series. Of the remaining 37 reports, 29 contained data for patients with tumors of varying sizes that could not be separated into subgroups based on the size of the tumor at the time of treatment. The remaining eight articles reported 5-year mortality rates by tumor size, specifically for small, medium, or large tumors. The combined weighted estimates of 5-year mortality rates following enucleation were 16% for small tumors (95% confidence interval [CI]: [14%, 18%]), 32% for medium tumors (95% CI: [29%, 34%]), and 53% for large tumors (95% CI: [50%, 56%]). Different methods of pooling the data yielded consistent estimates for all three tumor size categories.(ABSTRACT TRUNCATED AT 250 WORDS)

Choroid Neoplasms↗
PubMed1992

Patient and clinic factors predictive of missed visits and inactive status in a multicenter clinical trial. The Macular Photocoagulation Study Group.

Obtaining complete patient follow-up in clinical trials is important for the analysis of treatment results and for good patient care. Incomplete data can introduce bias into study results and can alter conclusions concerning treatment efficacy. The purpose of this study was to explore in a case-control design patient and clinic factors that may be associated with missed visits or inactive status within three clinical trials conducted as part of the Macular Photocoagulation Study. All inactive patients, all patients with any missed visits, and a random sample of patients with no missed visits were selected for interview. A total of 175 patients (60% of 292 selected) participated in the study. Two factors were found to be significantly associated (P less than .05) both with inactive status and with having any missed visits: health problems and travel costs. Several patient and clinic factors were found to be associated only with inactive status. These included change in marital status since joining the study, retirement since study entry, unsatisfactory interactions with the study physician or clinic coordinator, too little time spent with the study physician, and patient's belief that participants should be paid to participate in clinical trials. Distance from the clinic greater than 100 miles, in addition to health problems any time during follow-up and problems with travel costs, was found to be associated only with having any missed visits. This study emphasizes the importance of maintaining good patient-staff interactions and sensitivity to the events in a patient's life in order to obtain complete patient follow-up.

Bias↗
PubMed1991

Data monitoring committees for multicenter clinical trials sponsored by the National Institutes of Health. I. Roles and membership of data monitoring committees for trials sponsored by the National Eye Institute.

The operational aspects of data monitoring committees for multicenter clinical trials have received little attention in the published literature, in contrast to a wealth of publications concerning the statistical aspects of data monitoring. Occasional anecdotal reports suggest that the role of these committees is complex and that responsibilities and decisions extend beyond choice of a stopping rule. In an effort to gain a better appreciation of the domain of responsibilities shared by all or most of the data monitoring committees (DMCs) for the 20 multicenter studies (30 clinical trials) sponsored by the National Eye Institute, one of the National Institutes of Health, published information was studied and key members of the DMCs for these studies were surveyed. Information about the membership of these important groups also was sought in order to guide those with responsibility for appointing future DMCs. Three tasks--all directly associated with monitoring accumulating data for evidence of benefit or harm to trial patients--were reported unanimously to be the responsibility of the DMCs. In addition, many responsibilities concerned with study oversight rather than data monitoring were assigned to the DMC in 75% or more of the trials. The domain of responsibilities common to a majority of the DMCs suggests that these groups function in most NEI-sponsored multicenter trials as combined data monitoring and policy boards, even when not so designated. The median size of the 20 DMCs was 10 members, with six appointed and four ex officio members. Ophthalmologists accounted for 38% of all DMC positions and statisticians for 33%.

Clinical Trials as Topic↗
PubMed1990

Relationship between rate of patient enrollment and quality of clinical center performance in two multicenter trials in ophthalmology.

Those responsible for managing and overseeing multicenter clinical trials often express concern that differential rates of patients enrollment among participating clinical centers may be reflected in poorer compliance with study protocols or poorer patient care in the centers enrolling fewer patients. The purposes of the present investigation were (1) to determine whether rate of patient enrollment was related to other measures of clinical center performance in two multicenter clinical trials in ophthalmology, the Macular Photocoagulation Study (MPS) and the Early Treatment Diabetic Retinopathy Study (ETDRS), and (2) to compare findings from these two studies with findings reported from cooperative oncology groups. Percent of major data forms ever failing computerized edit was the only measure of performance examined that demonstrated a strong positive relationship to rate of patient enrollment in both studies under both analytic approaches employed (F test for linear trend in means and Spearman's rank correlation). In the MPS, but not in the ETDRS, percent of patients who had missed all visits scheduled during the past 12 months (inactive patients) also was related to rate of patient enrollment. However, the major finding from this investigation has been that it is not possible to predict overall performance of an individual clinical center based on rate of patient enrollment. Clinical centers enrolling fewer patients in these multicenter clinical trials performed in some areas as well as or better than centers enrolling larger numbers of patients.

Diabetic Retinopathy↗
PubMed1989

The use of fundus photographs and fluorescein angiograms in the identification and treatment of choroidal neovascularization in the Macular Photocoagulation Study. The Macular Photocoagulation Study Group.

The Macular Photocoagulation Study (MPS) Fundus Photograph Reading Center has developed a standard set of methods for assessing color photographs and fluorescein angiograms on study patients. For pretreatment angiograms, these methods are used to determine the location and extent of the choroidal neovascularization. For posttreatment color fundus photographs, these methods are used to assess the extent and intensity of treatment. Although these methods were developed to judge eligibility and treatment of patients enrolled in the MPS, they provide an excellent way for all treating ophthalmologists to evaluate their patients' angiograms and to assess immediately the intensity and extent of laser photocoagulation. The technique requires a microfilm reader or slide projection device to determine the completeness of treatment. The authors superimpose independent drawings made from pre- and posttreatment photographs. The techniques described can be applied readily in clinical practice. Since persistent neovascularization is highly correlated with incomplete and/or inadequate photocoagulation treatment, clinicians may adopt these Reading Center techniques to minimize the frequency of persistent neovascularization and, possibly, to reduce the frequency of visual loss in treated eyes.

Choroid↗
PubMed1988

Selection of controls for clinical research studies in ophthalmology.

Ophthalmologists are becoming increasingly aware of the need for well-designed, controlled studies to investigate etiology and treatment of ocular conditions. While patients with the conditions of interest, or with characteristics that place them at high risk of eventual development of such conditions, may be readily identified in the ophthalmology clinic, identification of appropriate controls to be used for comparison may be quite difficult. In this article, epidemiologic principles for selection of controls for retrospective (case-control) and prospective (cohort) studies are reviewed. Two related studies, a case-control study in which multiple control groups were employed and a 15-year cohort study of all cases and controls, provided an opportunity to compare controls selected at random from an ophthalmology practice with controls selected at random from the general population. Participation rates were higher among office patients selected for study, both in the case-control study and in the cohort study. In the cohort study, office controls were more likely to lose visual acuity and to develop new degenerative eye conditions. These differences between control groups selected from two different sources emphasize the need for careful evaluation of potential groups of controls with respect to biases that each may bring to interpretation of clinical research findings.

Biometry↗
PubMed1988

Enucleation versus plaque irradiation for choroidal melanoma.

The Collaborative Ocular Melanoma Study (COMS) is an international, multicenter-controlled study. The organization includes an Executive Committee, Steering Committee, 6 Central Units, 32 Clinical Centers, and a Data and Safety Monitoring Committee. Scientifically, the COMS consists of (1) a randomized trial of patients with medium choroidal melanoma treated with enucleation versus iodine-125 plaque irradiation, (2) a randomized trial of patients with large choroidal melanoma treated with enucleation versus preenucleation external beam irradiation and enucleation, and (3) a prospective observational study of patients with small choroidal melanoma to determine whether a randomized trial of treatment is appropriate. In design and conduct of the COMS, special consideration is given to biostatistics and sample size considerations, iodine-125 plaque irradiation of choroidal melanoma, and coordinated ocular melanoma research. Recruitment is in progress. However, the pool of eligible patients is limited and the COMS needs the continued support and cooperation of ophthalmologists throughout the United States and Canada.

Brachytherapy↗
PubMed1986

Subfoveal choroidal neovascular membranes in age-related macular degeneration. Visual prognosis in eyes with relatively good initial visual acuity.

We determined the visual prognosis of 94 eyes in 92 patients having age-related macular degeneration, a discrete choroidal neovascular membrane directly under the center of the foveal avascular zone (subfoveal), and an initial visual acuity of 20/100 or better. Of the patients who were reexamined 24 months following their initial presentation, 77% had lost at least four lines of vision and 64% had lost at least six lines. Estimation of visual loss using a conservative assessment procedure showed four-line visual loss in 65% of the patients and six-line loss in 50%. In general, the better the visual acuity at the initial examination, the more likely the patient was to have a smaller choroidal neovascular membrane. These results suggest that it may be reasonable to consider a randomized clinical trial of laser photocoagulation for this group of patients with a relatively poor visual prognosis.

Age Factors↗
PubMed1986

The Markov process as a general method for nonparametric analysis of right-censored medical data.

The product limit method of Kaplan and Meier for estimating survival functions and the logrank test of Mantel are widely employed for analysis of longitudinal medical data. Developed for analysis of one-time events such as death, survival analysis is also commonly adapted to more complex states such as loss of vision or cancer remission by restricting analysis to first occurrences. The nonparametric discrete time nonhomogeneous Markov process is proposed as a better model for any applications of the latter type. This simple stochastic model allows for an arbitrary number of possible states and for transitions in any direction. Maximum likelihood estimators are easily computed for the stochastic model and are identical to the product-limit estimates in the special case represented by the Kaplan-Meier model. The logrank test extends to evaluation of differences between populations with respect to any specified transition.

Actuarial Analysis↗