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Biomedical subjects

J T Barr

Publications and source records attributed to J T Barr.

At least 37 records · Page 2Linked to original sources
PubMed1997

Rigid gas-permeable contact lenses in high and low humidity.

BACKGROUND: Contact lenses may alter tear film evaporation. Evaporation varies with respect to air temperature and relative humidity. Hence, tear evaporation may be a significant factor for many occupations, such as military pilots, in the arid environments in which they operate. METHODS: The study tested rigid gas-permeable (RGP) contact lens wearer comfort and corneal staining in lower and higher relative humidity environments. RESULTS: A trend was found that in a lower humidity environment, RGP contact lens comfort may decrease for some subjects. Corneal surface integrity was not compromised by the variation in relative humidity level, as determined by fluorescein dye analysis. CONCLUSION: Within the range of humidity tested, for normal successful RGP patients, drier environments do not substantially reduce lens comfort.

Adult↗
PubMed1996

Biomicroscopic signs and disease severity in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group.

The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Survey represents the largest sample of clinic-based keratoconus patients to date. Data were collected at 38 clinical centers on 1,579 keratoconus patients. This article reports demographic variable, ages, self-reported ages at diagnosis, keratometry, slit-lamp findings, systemic disease, family history of keratoconus, and best spectacle-corrected and contact lens-corrected visual acuity of this sample group. The average age of this clinic-based sample group was 37 years (range 10-89 years), with 84% between 20 and 49 years old. Thirteen percent of patients had unilateral keratoconus, defined as unilateral corneal irregularity. More advanced disease (steeper average keratometric reading) was associated with a greater likelihood of Vogt's striae, Fleischer's ring, and/or corneal scarring. Fifty-eight percent of the eyes in this group of patients had > or = 20/40 visual acuity with manifest refraction. Penetrating keratoplasty was reported in 12.3% of eyes. This prospective survey identifies the associates between the presence of Vogt's striae, Fleischer's ring, and/or corneal scarring and increasing steepness, as measured by keratometry.

Adolescent↗
PubMed1996

Characteristics of corneal staining in hydrogel contact lens wearers.

Corneal fluorescein staining is widely used in clinical practice and research, but little information exists on the distribution of staining in a large group of asymptomatic contact lens wearers. This cross-sectional study took place at 3 centers, and investigated the pattern of corneal fluorescein staining in both eyes of 98 hydrogel contact lens wearers. We also investigated the strategies used by three experienced clinicians to grade corneal staining. Overall corneal staining was graded using a scale from 0 to 4 in one-half steps, and five corneal zones, superior, inferior, nasal, temporal, and central, were also graded. The average overall staining grade for both eyes of our subjects was 0.50, with an average of 0.57 for the right eye and 0.44 for the left. This difference between the eyes was statistically significant (p = 0.011). In addition, a comparison of the zones within each eye showed a significant difference (p = 0.0001) among the zones. Corneal staining between the two eyes was also positively and significantly correlated (r = 0.58; p = 0.0001). Grading strategies among clinical investigators were significantly different (p = 0.0001), indicating a potential source of bias in multi-centered studies. The difference in corneal staining between the eyes may represent a source of systematic bias, and could be due to grading the right eye before the left. The correlation in corneal staining between the eyes indicates that the two eyes of a subject cannot serve as independent data points. One-third of the subjects who participated in this study had notable corneal staining. This finding underlines the importance of regularly checking corneal staining in clinical practice.

Contact Lenses↗
PubMed1996

Standardized rigid contact lens fitting protocol for keratoconus.

Keratoconus is typically managed by a variety of rigid contact lens fitting techniques and lens designs. The two most fundamental fitting techniques are apical corneal touch (including divided or three-point touch) and apical clearance. In the course of designing a multi-center study of keratoconus patients, a standardized keratoconus fitting protocol was developed. All contact lens parameter options are uniform except for base curve and secondary curve radii, which are determined by interpretation of fluorescein patterns using the CLEK Study trial lens set and protocol. The initial trial lens's base curve is the average keratometric reading; sequentially steeper lenses are applied until definite apical clearance is observed. We have evaluated the feasibility of this standardized fitting protocol on 30 keratoconus patients. Our results suggest that we have developed a standardized contact lens fitting set and fitting protocol to simplify contact lens management in patients with mild to moderate keratoconus.

Contact Lenses↗
PubMed1996

Feasibility of fitting contact lenses with apical clearance in keratoconus.

Despite the wide variety of rigid contact lens fitting philosophies for the visual correction of keratoconus, questions remain, including which approach-flat, divided support, or steep-contributes the most toward the preservation of a clear cornea. One goal of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Pilot Study was to determine the feasibility of managing early keratoconus patients with apical clearance rigid contact lenses. Of 30 keratoconus patients identified with at least 1 nonscarred cornea, 17 patients (30 eyes) were randomly assigned to a steep lens fitting protocol. After trial fitting with a standardized lens design demonstrating minimum apical clearance, lenses were dispensed whose base curve was 0.2 mm steeper than the minimum apical clearance lens. Patients were re-evaluated on a quarterly schedule concluding at 12 months. Changes in keratometry between baseline and 12 months identified unequal steepening of the flat and steep corneal curvatures, suggestive of corneal molding. Best corrected rigid lens visual acuity measures illustrated no significant changes over the course of the study. Clinically significant corneal compromise was transiently observed in some patients. Only 1 of 22 eyes completing the pilot study and fitted with apical clearance developed mild corneal scarring.

Adolescent↗
PubMed1996

Corneal response and vision with the Softperm lens in simulated aircraft conditions.

BACKGROUND: Contact lenses are generally more compatible than spectacles with the life-support systems, personal protective devices, and helmet-mounted targeting systems used in modern military aircraft. This study evaluated the Softperm contact lens in a simulated aircraft environment to determine its potential use by USAF aviators. METHODS: Thirteen subjects wearing Softperm lenses were exposed to a simulated aircraft environment for 2 hours. Subjects were evaluated for signs of hypoxic stress by measuring corneal thickness changes and observing changes in corneal staining and conjunctival injection. Changes in visual acuity were also measured. Slit lamp biomicroscopy was used to assess lens movement at the beginning and end of the treatment period to determine if lens fit changed. Over-refractions to determine residual astigmatism were performed to evaluate how well the Softperm lens corrected astigmatic refractive errors. RESULTS: A statistically significant increase in corneal thickness was found after two hours of Softperm wear in the simulated aircraft environment. Several subjects experienced an increase in epithelial staining, which appears to be associated with changes in lens fit (tightening). All subjects experienced conjunctival injection. Residual astigmatism secondary to lens flexure occurred in all but two eyes, but no eyes had greater than 0.75 diopters. CONCLUSIONS: When properly fitted, the Softperm lens can be safely worn in an aircraft environment similar to the one simulated in this study. This lens design may provide an alternative to the lenses presently approved for USAF aviators.

Adult↗
PubMed1995

The outcomes movement and health status measures.

The outcomes movement is exemplified by clinical effectiveness studies incorporating patient-centered outcomes measures. Findings from these studies are used to base payment decisions and improve the structure and process of clinical practices. The usefulness of these studies is dependent upon the selection of appropriate outcomes measures. Typically, clinical measures used by health professionals are narrowly focused and assess physiologic, other biomedical, or limited functional dimensions of health. On the other hand, patient-centered outcome measures are more broadly defined and capture health status as perceived by the patient in areas of health identified to be of value to the patient. An introduction to multidimensional general and disease-specific health status measures is presented. Health status and other outcomes assessments should be part of a continuous quality improvement cycle which begins with measuring patient status and developing treatment plans, proceeds to monitoring patient progress, evaluates the clinical effectiveness of the service, and concludes with outcomes information being fed back to improve the structure and process of future health care services before the cycle can begin again.

Attitude to Health↗
PubMed1995

A teaching strategy to incorporate patient-centered outcomes assessment in health professional curricula: the class-generated patient profile.

As chronic diseases claim a growing proportion of our population's morbidity, health practitioners are increasingly concerned with the impact of diseases on the physical limitations, psychological status, social role, and overall quality of life of patients. While health professionals have traditionally supplemented their clinical assessment skills with physiologic measures such as temperature, white cell counts, pulmonary function tests, and enzyme levels, as well as functional measures such as range of motion and mobility, they are less facile with measures that describe the limitations in physical, psychological, and social functioning of patients. These latter factors may have a greater overall influence on patient status than physiologic and function indices alone.

Allied Health Occupations↗
PubMed1995

Keratoconus.

Keratoconus is characterized by the presence of corneal distortion (secondary to thinning of the apex) and either Fleischer's ring (found in 57% of patients) or Vogt's striae (found in 44% of patients). Often the only presenting symptom is decreased visual acuity. Steep keratometric readings are not usually diagnostic; 18% of patients with keratoconus have readings flatter than 45.00 D. Treatment requires correction of acuity with spectacles or contact lenses. More advanced cases are generally managed with rigid gas-permeable contact lenses. Corneal scarring occurs in approximately 43% of cases; 10% to 20% of patients require penetrating keratoplasty to restore acuity.

Contact Lenses↗
PubMed1994

Mild theophylline-related adverse reactions and serum theophylline concentration.

The relationship between theophylline-associated adverse drug reactions (ADRs) and serum theophylline concentration (STC) was studied. Patients with obstructive airway disease who received theophylline on the pulmonary ward of a large urban hospital over a 10-month period were included in the study. Each patient was interviewed within two hours after collection of a sample for determining STC and, without knowing the STC, the interviewer classified each patient into one of the following categories: ADR, no ADR, or indeterminant (symptoms similar to a theophylline-associated ADR but possibly caused by concomitant drugs or comorbidities). ADRs were also classified as to their severity. The interviewer identified 340 ADRs during 201 interviews of 126 patients. All but four of the ADRs were mild. In half of the interviews, patients reported at least two concurrent ADRs. Not including the indeterminant group, ADRs occurred in 69% of the patients, a much higher frequency than previously reported. The mean +/- S.D. STCs for the ADR and no-ADR groups were 6.5 +/- 1.7 and 7.7 +/- 2.0 micrograms/mL, respectively. When the indeterminant ADRs were added to the theophylline-associated ADRs, the resulting group had a mean +/- S.D. STC of 11.5 +/- 3.3 micrograms/mL. No significant association was found between STC and occurrence of ADRs. Theophylline-associated ADRs occurred more frequently than expected at STCs within and below the usually accepted therapeutic range.

Adverse Drug Reaction Reporting Systems↗
PubMed1994

Bayesian and threshold probabilities in therapeutic drug monitoring: when can serum drug concentrations alter clinical decisions?

The use of Bayesian and threshold probabilities is examined with respect to the range of probabilities of toxicity for which obtaining a patient's serum drug concentration leads to information that is potentially useful in altering a clinical decision. For the situation of potential drug-induced toxicity, three threshold probabilities are needed to characterize the decision process: the decision threshold for deciding between continuing and discontinuing the drug regimen, the testing threshold that separates the decision to continue the regimen without testing the serum drug concentration from the decision to test before deciding, and the companion testing threshold that separates the decision to discontinue the regimen without testing from the decision to test before deciding. For digoxin, theophylline, aminoglycosides, vancomycin, and phenytoin, three prototypical decision threshold probabilities, 0.33, 0.2, and 0.1, are used, along with published true-positive and false-positive rates, to calculate serum concentration testing thresholds for each drug. Practitioners can be more effective in their use of serum drug concentration data when a Bayesian approach to probability assessment is used in conjunction with testing thresholds.

Bayes Theorem↗
PubMed1994

Central and peripheral corneal thickness in keratoconus and normal patient groups.

Central and peripheral (superior, inferior, nasal, and temporal) corneal thickness was measured in patients with and without keratoconus using ultrasonic pachometry. In 28 normal eyes (14 patients) mean central corneal thickness (CCT) was 0.56 +/- 0.02 mm and the mean difference in thickness between the mean peripheral corneal thickness (PCT) and CCT was 0.24 mm. In 28 keratoconic eyes (14 patients) CCT was 0.52 +/- 0.04 mm, and PCT-CCT was 0.29 mm. For keratoconic right eyes, CCT and PCT-CCT were significantly different from normals (p = 0.01). Additional studies within the normal patient group showed no diurnal or day-to-day variations in CCT; they also confirmed the repeatability of the measurements.

Adult↗
PubMed1994

Applying decision analysis to pharmacy management and practice decisions.

Decision analysis, a structured approach to decision making, is presented and applied to a typical management situation. Decision analysis is an explicit, quantitative, and prescriptive approach to choosing among alternative outcomes. It engenders in the decision maker an analytical viewpoint, the need to structure the various courses of action and the resultant consequences of the actions, to assess the degree of uncertainty of the actions occurring, and to value the preferences for the alternative outcomes. Literature examples of using pharmacy-related decision analysis are provided, including its use in formulary additions, cost-effectiveness analysis, drug therapy evaluation, therapeutic drug monitoring, and health policy issues.

Cost-Benefit Analysis↗
PubMed1993

Transient rigid lens-induced striae in keratoconus.

We have observed spontaneous development of striae and an enhanced visibility of them after placing rigid gas permeable contact lenses on six patients suspected of having early keratoconus. These fine folds subside upon removal of the rigid lens. This observation assists clinicians with the differential diagnosis of irregular astigmatism when the definitive biomicroscopic signs of keratoconus are either not present or are so subtle that their presence is questionable. Although these striae may not occur in all patients suspected of having early keratoconus, we find that observation of the posterior cornea in the presence of a rigid lens will often confirm the diagnosis of keratoconus. We have not seen similar striae in patients whose clinical presentation is not consistent with early keratoconus.

Adolescent↗
PubMed1991

Use of a clinical data registry to evaluate medical technologies. Experience from the International Bone Marrow Transplant Registry.

We reviewed the 18 disease-specific evaluations that used the data base of the International Bone Marrow Transplant Registry to determine the effectiveness of alternative strategies for bone marrow transplant. We identify 17 treatment variables that physicians can control and report the associations between these variables and five clinical endpoints: stable engraftment, graft-versus-host disease, development of interstitial pneumonia, relapse, and disease-free survival. We also suggest policies to promote active participation in establishing and operating a registry.

Bone Marrow Transplantation↗
PubMed1991

Test performance characteristics of the serum phenytoin concentration (SPC): the relationship between SPC and patient response. The Veterans Administration Epilepsy Cooperative Study Group.

A retrospective analysis of Veterans Administration (VA) Cooperative Study No. 118 was conducted to examine the relationship between serum phenytoin concentration (SPC) and various measures of patient response in 111 patients on monotherapy, mostly after 12 months of treatment. Using patient response rating scales specifically developed and validated for the VA study, we plotted SPC vs overall composite score as well as vs each of the three component ratings of neurotoxicity, systemic toxicity, and seizure type and frequency. No statistically significant association was noted between SPC and any of the response measures. We also calculated test performance characteristics for using SPC and a therapeutic range of 10-22 micrograms/ml to categorize patient status with regard to overall response, toxicity, and seizure frequency. Test sensitivities (0.13-0.53), specificities (0.62-0.81), and positive predictive values (0.08-0.44) were much lower than desirable. This results in a large proportion of false-positive and false-negative errors associated with the use of SPC as a test. Our retrospective evaluation suggests that the range of SPC values in successfully treated patients is quite broad; the value of the commonly accepted SPC therapeutic range in predicting various measures of patient response is quite limited; and patient response, therefore, should be the ultimate end point in monitoring patients on phenytoin. Prospective studies of the relationship between SPC and response should be conducted.

Double-Blind Method↗