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Biomedical subjects

T Olsen

Publications and source records attributed to T Olsen.

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

Biomechanical characteristics of the human anterior lens capsule in relation to age.

PURPOSE: The purpose of the study was to investigate the influence of age on the biomechanical properties of the human anterior lens capsule. METHODS: The material comprised 67 lens capsules obtained from human donors ranging in age from 7 months to 98 years. Test specimens were prepared from the anterior lens capsule as tissue rings by means of excimer laser technique using a metal ring (mask) to shape the laser output (outer diameter = 3.2 mm, width = 100 microns). Capsular thickness was measured under microscope as the difference in focus between microspherules placed on the outer and inner surfaces of the capsule. The rings were slipped over two pins connected to a motorized micropositioner and a force transducer, respectively, and stretched at constant speed until rupture, with continuous recording of load and elongation. RESULTS: Capsular thickness was associated significantly with age of the donors and increased gradually (1.2% per year) until age 75, after which a slight decrease was observed. The elastic response curves showed a high degree of nonlinearity and were influenced markedly by age. Ultimate strain decreased 0.5% per year (range, 108% to 40%). Ultimate tensile strength decreased 1% per year (range, 17.5 N/mm2 to 1.5 N/mm2), and ultimate elastic stiffness (tangent modulus) decreased 0.9% per year (range, 44.8 N/mm2 to 4.4 N/mm2), whereas elastic stiffness corresponding to a specific strain level (30%) increased until age 35, after which a slight decrease was observed. CONCLUSIONS: Aging of the human anterior lens capsule is associated with a progressive loss of mechanical strength. The young capsule is strong, tough, and highly extensible, whereas the older, thicker capsule is less extensible and much more brittle, and it has a markedly reduced breaking strength.

Adolescent↗
PubMed1996

Predicting the refractive result after cataract surgery.

PURPOSE: To study the accuracy of predicting visual results after cataract surgery using a mathematical model of surgically induced refractive change and a previously published regression formula predicting uncorrected visual acuity as a function of the resulting spherocylinder. SETTING: Outpatient cataract clinic at a university hospital. METHODS: In this prospective study with a 4 month follow-up, 333 patients had phacoemulsification using a 6 or 4 mm scleral tunnel incision. Final refraction and uncorrected visual acuity were predicted based on preoperative and 1 day postoperative measurements, which were compared with the final visual results. RESULTS: A significant correlation was found between the observed and the predicted visual acuity in each eye (P < .01). CONCLUSION: The visual outcome of cataract extraction can be predicted from a theoretical model of the surgically induced refractive change.

Adult↗
PubMed1996

Evaluating surgically induced astigmatism by Fourier analysis of corneal topography data.

PURPOSE: To evaluate surgically induced astigmatism using Fourier harmonic series analysis of corneal topography data. SETTING: Aarhus Kommunehospital, Aarhus University, Denmark. METHODS: We evaluated the results of 46 phacoemulsifications with a 4 or 6 mm scleral tunnel sutureless incision based on the axis of the steepest meridian. We performed conventional keratometry and corneal topography before and up to 1 month after surgery. Using Fourier analysis, the corneal topographic images were broken into spherical power, regular astigmatism, and nonregular astigmatism for individual or aggregate analysis of surgically induced astigmatism. The induced refractive change (average of the difference between preoperative and postoperative corneal topographies) was analyzed and normalized according to the surgical meridian and to right/left eye. RESULTS: Regular astigmatism calculated by Fourier analysis of mires from the keratometer zone correlated well with conventional keratometry readings. Surgery induced a localized flattening in the superior region and a with-the-rule regular astigmatism component in the central area. CONCLUSION: Surgically induced corneal topography changes can be analyzed by Fourier series harmonic analysis, allowing aggregate data to be broken into optically meaningful quantities.

Adult↗
PubMed1996

Predictors of outcome for treatment of temporomandibular disorders.

Psychosocial factors have been frequently suggested as important risk factors that may delay recovery in patients with temporomandibular disorders. In this study, 94 subjects with chronic temporomandibular disorders were studied using IMPATH:TMJ prior to their entering an interdisciplinary treatment program to determine which factors were most predictive of outcome. Treatment outcome was determined based on significant decreases in the Craniomandibular Index and the Symptom Severity Index from pretreatment to posttreatment. The IMPATH:TMJ items were regressed on treatment outcome for a random sample of half of the subjects (n = 47) to isolate the psychosocial and demographic items most predictive of treatment response. Discriminant analysis was then employed to test the predictive utility of the identified items for these subjects (criterion group), followed by a cross-validation of the items on the remaining 47 subjects (cross-validation group). Low self-esteem, feeling worried, low energy, and sleep activity were identified as useful predictors of treatment outcome for the criterion group. Each are correlates of depression. The discriminant analysis employing these four items accounted for 49% of the variance in treatment response, was statistically significant (P < .0001), and correctly predicted treatment outcome for 41 of 47 subjects (87%) in the criterion group. The predictive utility of the identified items remained statistically significant when applied to the cross-validation group (P < .01). The discriminant function employing the items correctly predicted treatment outcome for 37 of 47 subjects (79%) and explained 28% of the variance in treatment response. Findings of this study suggest that pretreatment psychosocial information is important in predicting treatment outcome for chronic temporomandibular disorders, and that symptoms of depression mediate treatment response for chronic pain patients.

Adolescent↗
PubMed1995

Efficiency and accuracy of disease monitoring systems: application of capture-recapture methods to injury monitoring.

Capture-recapture methods were employed to determine the most accurate and efficient approaches to monitor adolescent injuries. Multiple sources were used to ascertain cases of adolescent injuries that occurred between September 1 and December 31, 1991, in a single school district in metropolitan Pittsburgh, Pennsylvania. Eliminating the duplicate cases between the sources revealed 144 verified injuries; 127 (88.2%) were identified by student monthly recalls, 33 (22.9%) by daily attendance records, 58 (40.3%) by medical excuses, and 72 (50.0%) by a 4-month student recall. Capture-recapture analyses were undertaken to assess potential dependencies between the sources, to estimate the degree of underascertainment in the population, and to evaluate the efficiency of the individual sources and the combinations between them. It was estimated that 91% of the cases in the population were ascertained when all four methods of case finding were utilized. Furthermore, the analysis indicated that accurate injury estimates could be achieved using combinations of only two or three of the sources. An analysis of the efficiency of the methods of ascertainment revealed a trade-off between effort (the number of hours needed to identify cases) and the precision (coefficient of variation) of the injury estimates. Capture-recapture analysis not only provided an approach to evaluate and adjust for undercount but also offered a formal means to evaluate the most efficient combination of the sources to maximize completeness while minimizing effort. The use of these techniques has the potential to evaluate and improve injury surveillance as well as other disease monitoring systems.

Adolescent↗
PubMed1995

Intraocular lens power calculation with an improved anterior chamber depth prediction algorithm.

The accuracy of intraocular lens (IOL) power calculation was evaluated in a multicenter study of 822 IOL implantations using the Binkhorst II, Sanders/Retzlaff/Kraff (SRK I, SRK II, SRK/T), Holladay, and Olsen formulas. All but the first of these were optimized in retrospect with calculation of the SRK A-constant, the Holladay surgeon factor, and the Olsen pseudophakic anterior chamber depth (ACD) for each lens style. The ACD prediction of the Olsen formula was based on a previously described regression formula incorporating preoperative ACD, corneal height, axial length, and lens thickness. Among the optical IOL power calculation formulas, the highest IOL power prediction error was found with Binkhorst's and the lowest with Olsen's, which was more accurate than the SRK/T and the Holladay formulas (P < .05). The SRK/T formula was significantly more accurate than the original SRK regression formulas (P < .001). When analyzed for axial length dependence, all formulas showed the least error in the normal range. Error of the Olsen formula was lower than that of the others in the axial length interval 20 mm to 26 mm. No differences in accuracy were found between the optical IOL calculation formulas in eyes with an axial length above 26 mm (P < .05). The accuracy of IOL power calculation can be improved with optical formulas using newer-generation ACD-prediction algorithms.

Adult↗
PubMed1995

Video controlled M-mode biometry.

To increase the accuracy of intraocular lens power calculation, an interface between an ultrasonic A-scanning device and a personal computer was created, allowing for an on-line interpretation of the ultrasonogram in an M-mode fashion. On the same computer display, a video recording of the movements of the transducer probe relative to the eye was inserted to obtain simultaneous information on the external alignment of the transducer probe. The precision of the experimental set-up in the measurement of intraocular distances was compared with conventional A-scanning procedures run in automatic mode. The video controlled M-mode biometry was found easy to operate and to result in reproducible axial length determination: The median value of the standard deviation was found to be below 0.04 mm as compared to a value of about 0.10 mm with conventional equipment. We concluded that video controlled M-mode biometry has great potential in the endeavour to increase the accuracy of intraocular lens calculation.

Anterior Chamber↗
PubMed1995

Outcome monitoring in cataract surgery.

The short-term surgical results are reported in a consecutive series of 1473 patients undergoing cataract surgery (60% planned extracapsular cataract extraction and 40% phacoemulsification) on an out-patient basis in a major university eye clinic. Preoperatively, 80% of all cases had a visual acuity of 0.3 (6/18) or lower. On the first day after surgery, 51% of all patients had a corrected visual acuity of 0.5 (6/18) or better and 9% had a visual acuity of 1.0 (20/20) or better. The unaided visual acuity was 0.5 (6/12) or better in 20% of all patients (78% of these after phaco-emulsification). The average postoperative refraction was -0.43 D (+/- 1.03 D SD, range -6.00 D to +5.00 D). A significant improvement in refractive error was achieved in many patients. The mean intraocular lens power prediction error was found to be +0.04D (+/- 0.84D). The surgically induced astigmatism (vector analysis) was found to be +4.91D (+/- 2.08) in the extracapsular cataract extraction cases and +1.37D (+/- 1.38) in the phacoemulsification cases (p < 0.001). Capsular or zonular rupture and/or vitreous loss occurred in 43 (2.9%) of which 26 (1.8%) received an anterior chamber lens rather than the intended posterior chamber lens. The results of this study document the favorable results of modern cataract surgery.

Adolescent↗
PubMed1995

Psychosocial benefits of postmastectomy lymphedema therapy.

The effect of a comprehensive lymphedema management program was assessed in 25 patients in whom moderate to severe lymphedema had developed after surgery and/or radiotherapy for carcinoma of the breast. Intensive treatment (4 weeks) involved massage, compression bandaging, and sequential pneumatic compression, with an adjunct program of education to provide skills in exercise, massage, bandage, and containment garment use. The intensive treatment phase was followed by a self-management phase based on the skills that had been acquired. A significant reduction in limb circumference and volume, with continuing improvement over 12 months of self-management, was observed. There was a decrease in need for physical assistance. Quality of life generally remained high and stable throughout the 12 months. Quality of life specific to lymphedema, however, declined during the intensive phase of treatment, but recovered and surpassed pretreatment levels during the self-management phase of treatment. Perceived comfort and strength in the lymphedematous limb improved, and perceived size decreased. The study confirmed that the combination of multimodal physical therapy and education for self-management reduces lymphedema and its adverse subjective consequences and maintains the improvement thus achieved.

Adult↗
PubMed1995

Physical activity and the initiation of high-risk health behaviors in adolescents.

The association of physical activity to the initiation of health risk behaviors was examined in a 3-yr prospective study of a population-based cohort of 1245 adolescents aged 12-16 yr. Four hundred thirty-seven students (35% of the cohort) were identified at baseline via self-report survey as never having smoked cigarettes, consumed alcohol, used marijuana, or carried a weapon. Three measures of physical activity were obtained at baseline: leisure-time physical activity (LTPA), level of aerobic fitness (AF), and participation in competitive athletics. Significant associations, with notable gender differences, were observed between physical activity and the initiation of cigarette smoking and alcohol use. The cumulative proportion of male students initiating alcohol use was 48%, 42%, and 24% for high, moderate, and low LTPA, respectively (P < 0.01). Males who participated in competitive athletics were significantly more likely than nonathletes to initiate alcohol use (44% vs 17%, P < 0.01). The cumulative proportion of female students initiating cigarette use was 10%, 23%, and 22% for high, moderate, and low LTPA, respectively (P < 0.05) and 7%, 28%, and 16% for high, moderate, and low AF, respectively (P < 0.05). No association was found between physical activity and weapon carrying. These results indicate that in this cohort of adolescents, the most active or most fit females were less likely to initiate cigarette smoking. In contrast, the most active males or males who participated in competitive athletics appeared more at-risk for initiating alcohol consumption than their less active counterparts.

Adolescent↗
PubMed1994

The role of socioeconomic status and injury morbidity risk in adolescents.

OBJECTIVE: To examine the patterns of socioeconomic status and injury morbidity in adolescents. DESIGN: Prospective cohort study. SETTING: Metropolitan school district in Allegheny County, Pennsylvania. PARTICIPANTS: There were 1245 students (89%) recruited from 1400 aged 12 to 16 years. INTERVENTIONS: None. MEASURES AND RESULTS: Baseline variables of socioeconomic status used for this analysis included township of residence (from the 1990 census data ranked by the percentage of households below the poverty level) and employment status of the parents (student self-report). Life-table analysis revealed no differential risk of injury by socioeconomic status. Similar results were found when stratified by gender, race, injury type (sport vs nonsport), and injury place (school vs home). CONCLUSIONS: The results indicate that in this cohort of adolescents, socioeconomic status does not seem to be a contributing risk factor for injury.

Adolescent↗
PubMed1994

Evaluating surgically induced astigmatism.

Using a modification of vector analysis for calculating surgically induced astigmatism, we describe a simple method that divides the induced cylinder into two orthogonal components. This decomposition allows with-the-rule and against-the-rule astigmatic changes to be calculated for individual case analysis, as well as for statistical analysis of aggregate data. Because it is based on the true induced cylinder, as determined by optical principles, this method overcomes some of the problems associated with earlier methods of evaluating surgically induced astigmatism.

Astigmatism↗
PubMed1993

Using the surgical result in the first eye to calculate intraocular lens power for the second eye.

This paper examines the possibility of using the surgical result in the first eye when planning the intraocular lens power for the second eye. Two methods were considered: (1) an empirical method by which one regards the second procedure as a repeat of the one in the first eye and calculates the power from the actual refractive error obtained in the first eye and (2) a theoretical method by which one measures the pseudophakic anterior chamber depth (ACD) of the first eye and uses this value to plan for the second eye. Based on the data from 136 second eye procedures using extracapsular cataract extraction, the prediction error of the empirical method ranged from -10.5 to +9.5 diopters. The error of the theoretical method ranged from -2.3 to +2.8 diopters, which was significantly more accurate than the empirical method (P < .001). We conclude that the fellow eye ACD may be used as a guideline for the assumed ACD of the second eye. However, such use of the fellow eye ACD could not be shown to improve power calculation predictions significantly.

Adult↗
PubMed1993

Phacoemulsification, capsulorhexis, and intraocular lens power prediction accuracy.

Phacoemulsification with capsulorhexis reduces the surgical variability and may result in a more predictable refractive outcome. To evaluate the prediction accuracy with current IOL power prediction formulas, we reviewed a retrospective series of 628 phacoemulsification cases, including 148 short (< 22 mm) and 80 long (> 25 mm) eyes. Using the Binkhorst II formula and the manufacturer's recommended anterior chamber depth (ACD) values, the mean absolute refractive prediction error was 0.56 diopters (D). This error could be reduced to 0.51 D by retrospectively optimizing the ACD values for each lens type. Under similar least error conditions, the mean error was 0.51 D with the SRK/T formula and 0.47 D with the Olsen formula (P < .01). The Binkhorst formula overestimated the refraction in short eyes and underestimated the refraction in long eyes. The SRK/T and the Olsen formula were unbiased with the axial length. We hypothesize that the high prediction accuracy may be partially explained by a more predictable pseudophakic ACD with the current surgical technique.

Anterior Chamber↗
PubMed1993

Contrast sensitivity and glare in patients with a diffractive multifocal intraocular lens.

Contrast sensitivity was measured in 25 patients who had a multifocal diffractive intraocular lens and in 23 control patients with a monofocal lens in four simulated light conditions: (1) daylight, (2) daylight with peripheral glare, (3) twilight, (4) twilight with central glare. In normal daylight and twilight, contrast sensitivity of the multifocal group was significantly lower than the control group's (P < .05). The difference was 0.13 log units for the multifocal group and 0.17 log units for the control group (mean value across the tested frequency from 1.5 to 18 cycles/deg). Peripheral glare reduced contrast sensitivity under daylight conditions in both groups (P < .05), but the loss did not differ significantly between the two (P > .05). Central glare reduced contrast sensitivity under twilight conditions in both groups (P < .05), with the greatest loss in the multifocal patients (P < .001). We conclude that the most significant loss of contrast sensitivity in patients with the diffractive multifocal intraocular lens is found with central glare under twilight conditions.

Aged↗
PubMed1993

On the Stiles-Crawford effect and ocular imagery.

To study the modifying effect on spherical aberration of the retinal directional sensitivity (the Stiles-Crawford effect), ocular imagery was simulated by computer ray-tracing in a phakic and a pseudophakic model eye. The Stiles-Crawford effect was found to reduce the distance between the paraxial focus and the effective least blur focus. The modifying effect on spherical aberration was found to be insignificant for pupil sizes below 4 mm, and to increase in magnitude above this size. For an 8 mm pupil, the effective focus was found to move 0.3 mm and 0.2 mm toward the paraxial focus for the phakic and the pseudophakic eye, respectively. This corresponded to a shift of 1.0 D and 0.6 D in the spectacle plane, respectively. The modifying effect of the retinal directional sensitivity should be taken into account in the theory of ocular refraction and in objective keratometry and refractometry.

Cataract↗
PubMed1993

IOL power mislabelling.

Prompted by four cases of IOL power mislabelling, a method was developed which allowed the measurement of the IOL power using a keratometer. The principle of operation was to measure the curvature of the steepest surface of the IOL through a minus lens by which the size of the mires was brought into the measuring range of the keratometer. With this method the IOL power was checked in three random IOL samples from three companies. Although no large errors in IOL power labelling were encountered in these samples, the error of labelling was found to differ significantly between the companies. It was concluded, that poor manufacturing control of IOL power may add to the sources of error in IOL power prediction.

Aged↗