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Biomedical subjects

W C Stewart

Publications and source records attributed to W C Stewart.

At least 127 records · Page 7Linked to original sources
PubMed1991

The effect of background intensity on the components of fluctuation as determined by threshold-related automated perimetry.

We studied the effect of various background intensities on the components of fluctuation by testing 20 healthy subjects on the Humphrey Field Analyzer. Our results show little difference in the total fluctuation between two low photopic background intensities similar to those commonly used on commercial perimeters: 3.02 dB for 31.5 apostilbs (asb) and 2.77 dB for 3.15 asb. However, an increase in total fluctuation (3.74 dB for 0.315 asb and 4.24 dB for 0.0315 asb) as well as in its short-term, long-term heterogeneous, and interindividual components was seen at mesopic background intensities as compared with the low photopic range. This study suggests that in healthy individuals, little difference exists in the fluctuation resulting from differences in background intensities commonly used on commercial perimeters, whereas mesopic illumination may increase the variability of threshold responses.

Adult↗
PubMed1991

Association of Vistech contrast sensitivity and visual field findings in glaucoma.

Single eye visual fields and contrast sensitivity were assessed in 60 subjects, who were being followed up in a glaucoma clinic for manifest glaucoma or a suspicion of glaucoma because of raised intraocular pressure. The Fieldmaster 5000 (static/kinetic perimeter) was used for the visual fields, and a Vistech wall chart sine wave grating test was used for contrast sensitivity measurements. The subjects were divided into three groups--defect (D), suspect (S) and normal (N)--on the basis of their perimetric findings by subjective grading of 16 perimetric scoring categories for each visual field. The mean Vistech sensitivity levels were not found to be significantly different between the D, S, and N field subgroups at any of the five spatial frequencies provided on the test charts (1.5, 3, 6, 12, and 18 cycles per degree). Complex algorithms combining results from two or more spatial frequencies also failed to yield any significant differences between the groups. Diagnostic sensitivity and specificities relating Vistech contrast sensitivity findings to groups N and D never concomitantly exceeded 60%.

Adult↗
PubMed1991

The use of a new portable noncontact tonometer in home tonometry.

We used a new portable noncontact tonometer for home tonometry on 26 patients with chronic open-angle glaucoma or suspected low-tension glaucoma. In an outpatient setting, the mean difference and correlation coefficient between the family member's noncontact tonometry values and the nursing staff's applanation tonometry values used as a control was 1.0mmHg and 0.894mmHg, respectively. The difference between the means was not statistically significant (P greater than .05, by Student's t test). At home, the variances of four noncontact tonometric values obtained every other hour did not differ significantly from those obtained in the outpatient setting by the nursing staff (P greater than .05). Five of 26 patients had their medical regimen changed based on the results of home tonometry. This study suggests that many nonmedical personnel can do noncontact tonometric scanning reliably. At home, noncontact tonometry may help evaluate a patient's intraocular pressure control.

Adult↗
PubMed1991

Transscleral cyclophotocoagulation using a semiconductor diode laser in cadaver eyes.

We studied the effectiveness of semiconductor diode laser transscleral cyclophotocoagulation in cadaver eyes using the Miyake technique and light microscopy. Thermal lesions in the ciliary processes were induced with 0.7-second, 1200-mW, and 100- to 500-microns applications, 0.5 mm from the surgical limbus and defocused 1 mm posteriorly. An effective ciliary body reaction was observed grossly as tissue blanching, shrinkage, and pigment dispersion; and histologically, as coagulation necrosis and epithelial cell disruption. No damage to crystalline or intraocular lenses was evident. This successful application of diode laser transscleral cyclophotocoagulation in cadaver eyes suggests that it may prove useful in treating patients with glaucoma.

Ciliary Body↗
PubMed1991

Response of argon laser trabeculoplasty with varying anterior chamber anatomy.

We studied one randomly selected eye of 50 consecutive primary open-angle glaucoma patients treated with argon laser trabeculoplasty to assess response differences as functions of anterior chamber anatomy and refraction. We found no significant differences related to these variables, and thus conclude that argon laser trabeculoplasty may be performed successfully in patients with crowded angles as long as the trabecular meshwork can be visualized.

Anterior Chamber↗
PubMed1991

A comparison of neodymium: yttrium aluminum garnet and diode laser transscleral cyclophotocoagulation and cyclocryotherapy.

The cyclodestructive effects of cyclocryotherapy and of the neodymium:yttrium aluminum garnet (Nd:YAG) and diode laser transscleral cyclophotocoagulation were investigated in phakic and pseudophakic cadaver eyes using a modified Miyake posterior-view technique and light microscopy. Cyclocryotherapy to -80 degrees C was applied with a 2.5-mm diameter tip, 1 and 2 mm from the limbus. Freezing at the ciliary processes was evident after 10-15 sec and reached a diameter of 3-4 mm by 30 sec. No visible changes were evident grossly in the ciliary processes, crystalline lens, or intraocular lens. Histologically increased separation of cells was observed. Effective noncontact Nd:YAG and diode laser applications to the ciliary processes were observed grossly as tissue blanching and shrinking and pigment dispersion. This effect was obtained by aiming 0.5-1.0 mm behind the limbus at a 1-mm defocus using 4 J of energy for the Nd:YAG and 1.2 J for the diode laser. The diode laser spot size did not affect the tissue response. No damage was observed in the crystalline or intraocular lens with either type of laser. Histologic changes using both lasers were coagulation necrosis with fragmentation and detachment of the ciliary body epithelium. This study suggested that the gross and histologic thermal effects produced by the diode and Nd:YAG laser were similar in the ciliary body. Also, at the time of surgery, these cyclodestructive procedures potentially cause little alteration of the crystalline or intraocular lens.

Ciliary Body↗
PubMed1991

The use of 5-fluorouracil in patients following combined trabeculectomy and cataract extraction.

We studied the effect of postoperative administration of subconjunctival 5-fluorouracil in maintaining postoperative filtration following combined trabeculectomy and extracapsular cataract extraction with posterior chamber lens implantation. Three months postoperatively, the mean intraocular pressure in 15 patients who had received 5-fluorouracil was 13.1 +/- 3.2 mm Hg; in 17 control patients, it was 13.0 +/- 3.0 mm Hg (P greater than .05). The mean number of postoperative medicines in the study patients was 0.7; in the control patients, 0.8 (P greater than .05). Bleb appearance and improvement in visual acuity were similar in the two groups. This study does not support the routine use of 5-fluorouracil in patients who have undergone combined trabeculectomy and extracapsular cataract extraction.

Aged↗
PubMed1991

Early postoperative prognostic indicators following trabeculectomy.

We compared prognostic indicators manifesting within the first 2 postoperative days, with filtration status 3 months following trabeculectomy in 51 primary open-angle glaucoma patients. Patients with an avascular area in the filtering bleb 2 days after surgery had a significantly lower (P less than .05) intraocular pressure (IOP) (12.6 mm Hg) 3 months postoperatively than patients with vascular blebs (16.3 mm Hg). However, neither the height, breadth, or transparency of the filtering bleb, presence of microcysts, anterior chamber depth, nor IOP during the first 2 postoperative days were related significantly to the filtration status at 3 months.

Female↗
PubMed1990

Factors that influence the prevalence of positive catch trials in glaucoma patients.

We evaluated factors that influence the catch-trial response in automated perimetry by consecutively examining 408 glaucoma patients (703 eyes) with either the program 30-2 or a 76-point screen with a quantified defect on the Humphrey Field Analyzer. The prevalence of positive catch trials using both programs was: 15.9% fixation losses, 5.5% false-positives, and 17.0% false-negatives. The only significant difference between the two programs was a lower prevalence of false-negatives on the program 30-2 (P less than 0.01). False-positive responses showed a significant positive correlation to fixation losses, and the catch trial response in general was correlated significantly to defect depth, test time, age, and visual acuity (P less than 0.05). This study suggests that the prevalence of positive catch trials is not an independent variable when testing glaucoma patients with automated perimetry and is not reduced by using a screening strategy over a full-threshold exam.

Adolescent↗
PubMed1990

Hemianopic offsets in the visual field of patients with glaucoma.

In 359 glaucoma patients (600 eyes), we measured the peripheral field with kinetic targets and the central 30 degrees field of vision with static testing, using the Field-master-5000 automated perimeter to evaluate the prevalence and significance of step-like visual-field defects along the vertical midline (a hemianopic offset). In all, 129 eyes of 121 patients had a hemianopic offset. In 108 eyes the offsets (involving either the peripheral or the central field or both) were associated with other glaucomatous field changes, whereas 21 eyes showed a peripheral offset as an isolated finding. Of the 8 cases of offsets found in both eyes, 7 were binasal and 1 occurred bitemporally but in separate hemifields. This study suggest that hemianopic offsets occur commonly in glaucoma patients but have limited diagnostic value because most are associated with other glaucomatous field changes. However, these findings help in distinguishing glaucomatous offsets from those caused by neurological lesions.

Glaucoma↗
PubMed1990

Static threshold variability in the peripheral visual field in normal subjects.

We assessed the variability of point-wise static threshold values and the components of fluctuation outside the central 30 degrees field in 20 normal individuals tested on the Humphrey field analyzer. We found a mean short-term fluctuation of 2.37 dB, a long-term heterogeneous fluctuation of 5.28 dB, and a long-term homogeneous fluctuation of 1.10 dB. All components of fluctuation were greatest superiorly. Point-wise variation was highest superiorly and nasally and increased with greater eccentricity from fixation in all but the temporal quadrant. Also, point-wise variation was greater between individuals than between tests in a single individual. This study suggests that outside the central 30 degrees field, changes in individual threshold measurements in the superior and nasal quadrants should be greater than those in the temporal or inferior quadrants before they can be distinguished from normal variation.

Adult↗
PubMed1990

Intraoperative epicardial echocardiography: technique and imaging planes.

With the recent innovations in cardiac surgical techniques, there is need for an immediate and reliable way to assess results in the operating room. Intraoperative epicardial echocardiography with Doppler color flow mapping provides an accurate and rapid imaging modality to assess the anatomical and functional results of cardiac surgery. This gives the surgeon a way to determine whether the hemodynamic abnormality has been successfully eliminated, prior to closure of the chest. After enclosure in a sterile sheath, a standard echocardiographic transducer is placed directly onto the epicardial surface. The heart is imaged in multiple tomographic planes developed specifically for intraoperative use: the parasternal equivalent; aortopulmonary sulcus; subcostal equivalent; and aorta-superior vena cava transducer positions. Two-dimensional echocardiography is useful to assess the morphology of valves and the size and function of cardiac chambers. Doppler color flow mapping provides a semi-quantitative assessment of the severity and physiological mechanism of valvular regurgitation. Continuous-wave Doppler echocardiography is used to estimate gradients across stenotic valves. This comprehensive appraisal of cardiac anatomy and flow is useful in the pre- or postcardiopulmonary bypass phase of cardiac surgery. This review focuses on the technique of intraoperative echocardiography and its applications in valve reconstruction operations with specific emphasis on the epicardial imaging planes.

Echocardiography, Doppler↗
PubMed1990

Threshold variability using different Goldmann stimulus sizes.

We tested 10 healthy subjects on the Humphrey Field Analyzer using Goldmann stimulus sizes I-V to determine the effect of varying the area of the stimulus upon threshold fluctuation. Our results show similar components of fluctuation for the size III stimulus as in past studies. However, an increased total fluctuation was observed for Goldmann stimulus sizes I (3.69 decibels) and II (3.17 decibels) and a similar fluctuation for stimulus sizes IV (2.64 decibels) and V (2.51 decibels) as compared to stimulus size III (2.52 decibels). The study suggests no advantage results in reduced threshold fluctuation by changing the Goldmann stimulus from a size III when testing normal individuals on the Humphrey Field Analyzer.

Adult↗
PubMed1990

Factors associated with a learning effect in glaucoma patients using automated perimetry.

We studied 45 primary open-angle glaucoma patients consecutively examined with the program 30-2 on the Humphrey Field Analyzer to determine factors associated with a learning effect between the first two visual field exams. The average mean defect significantly decreased 1.7 dB between exams (P less than 0.05). No difference was noted in learning based on: the time interval between tests, the area of the field tested, age, sex, race, previous perimetric experience or parameters on the initial field exam (i.e. prevalence of false positive and negative errors, central reference level and eye tested (P greater than 0.05). However, learning positively correlated to defect depth and negatively correlated to fixation losses on the initial exam in patients retested within seven months (P less than 0.05). This study suggests predicting which patients require a second baseline field exam to exclude a learning effect is difficult, except in those with glaucomatous field loss or few fixation losses and another field is planned within a half year.

Aged↗
PubMed1989

Full threshold versus quantification of defects for visual field testing in glaucoma.

Nineteen glaucoma patients, 17 ocular hypertensives, and 16 normal subjects underwent visual field testing on the Humphrey Field Analyzer using two programs: full threshold (thresholding of all test points with double-crossing technique) and quantification of defects (thresholding only points that deviated more than 6 dB from a presumed normal retinal contour). The purpose of the study was to compare the diagnostic value of information gained by the latter, less time-consuming test with that of the full threshold procedure. The average time requirement per eye was 13 min 11 s for full thresholding and 4 min 22 s for quantification of defects. Of the 104 sets of fields, the diagnosis was at variance in 18. The differences were most often due to shallow defects in otherwise normal fields or shallow defects surrounding deeper scotomas that had been detected by both programs. The shallow defects placed the fields in more advanced diagnostic categories and were all detected with the full threshold technique.

Diagnosis, Computer-Assisted↗
PubMed1988

Management of anterior chamber depth after trabeculectomy.

We followed up 36 eyes of 34 patients for the first three months after trabeculectomy, paying special attention to the depth of the anterior chamber. A significant difference in postoperative course was noted between those eyes with central cornea-lens touch and those with cornea-iris touch but not contact between cornea and lens. The former group (four eyes) had a high rate of complications, including corneal edema, cataract, and bleb failure, despite early efforts to reform the anterior chamber. The latter group (18 eyes), in which the anterior chambers were all allowed to reform spontaneously, had a favorable course, similar to those eyes that maintained formed anterior chambers throughout the study.

Adult↗
PubMed1988

Peripheral visual field testing by automated kinetic perimetry in glaucoma.

The peripheral visual field was measured with a single kinetic target and the central 30 degrees with static stimuli in 600 eyes of 323 patients with glaucoma and patients suspected of having glaucoma using an automated perimeter (Fieldmaster 5000). The purpose of the study was to compare the additional information gained by the peripheral field testing against the time requirement for this extra procedure. An abnormal peripheral field supported the diagnosis suggested by a central abnormality in 131 eyes (21.8%), while a defect in the peripheral field provided the principal diagnostic information, when the central field was normal or equivocal, in 25 cases (4.2%). Peripheral field measurements accounted for approximately 28% of the total testing time.

Glaucoma↗