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Biomedical subjects

A W Dreher

Publications and source records attributed to A W Dreher.

10 recordsLinked to original sources
PubMed2001

Detecting AMD with multiply scattered light tomography.

PURPOSE: to use a novel technique, Multiply Scattered Light Tomography (MSLT), to provide a comfortable, rapid, and noninvasive method for detection and management of Age-related Macualar Degeneration. METHODS: two patient groups were studied in clinical settings with MSLT and confocal scanning laser tomography. In Poway, CA, 21 retinal patients underwent tomography, and the 17 patients with suspicion of exudation also had ICG. An Angio-Scan (Laser Diagnostic Technologies, Inc.) was used to provide simultaneous fundus reflectance and ICG imaging. In Methuen, MA, 20 retinal patients underwent tomography with fluorescein angiography for suspicion of exudation. The MSLT was based on the TopSS (Laser Diagnostic Technologies, Inc.), with a Vertical Cavity Surface Emitting Laser array at 850 mm as the illumination source. The central laser produced confocal images. The surrounding lasers produced multiply scattered light images. RESULTS: MSLT emphasized structures beneath the retina such as drusen, choroidal new vessel membranes, and pigment epithelial detachments. Exudation seen on angiography was visualized by MSLT as topographical structures with distinct borders. Superficial structures, e.g., cysts and epiretinal membranes, were visualized in 850 nm images. DISCUSSION: confocal tomography and MSLT provided a rapid, noninvasive method to detect and localize macular degeneration and pathological structures found in eyes of older patients.

Adult↗
PubMed1998

Differentiating patients with glaucoma from glaucoma suspects and normal subjects by nerve fiber layer assessment with scanning laser polarimetry.

PURPOSE: A study was conducted to determine normative data for nerve fiber layer measurements as obtained by scanning laser polarimetry with the Laser Diagnostic Technologies Nerve Fiber Analyzer II, identify factors affecting the measurements, and identify parameters capable of differentiating normal subjects from patients with glaucoma and patients suspected of having glaucoma because of ocular hypertension or because of a large cup-to-disc ratio (GS-disc). DESIGN: A case series. PARTICIPANTS: Four hundred normal subjects, 35 patients with ocular hypertension, 42 patients with glaucoma, and 17 glaucoma suspects based on optic disc appearance participated. METHODS: Nerve fiber layer thickness assessments were determined in normal subjects (with normal-appearing optic nerves and normal visual fields). The results were compared to measurements from samples of age-matched patients with ocular hypertension (with normal visual fields), patients suspected of having glaucoma based on enlarged cup-to-disc ratios, and patients with open-angle glaucoma who had visual field loss. RESULTS: The majority of the parameters derived from the measurements showed no significant relationship to age, although some parameters tended to decrease with increasing age. Multiple parameters showed statistically significant differences between normal subjects and patients with glaucoma. In particular, the intraellipse sector variability, an indirect measure of the shape of the nerve fiber layer in an ellipse surrounding the nerve head, showed statistically significant differences between normal subjects and patients with glaucoma as well as between glaucoma suspects and normal subjects. Similar results were seen with the superior maxima, the average thickness assessment value of the 1500 thickest points in the superior bundle. CONCLUSIONS: Assessments of nerve fiber layer thickness as determined by scanning laser polarimetry can differentiate patients with glaucoma from normal subjects and may identify otherwise undetected damage in glaucoma suspects.

Diagnostic Techniques, Ophthalmological↗
PubMed1991

Reproducibility of topographic measurements of the normal and glaucomatous optic nerve head with the laser tomographic scanner.

We acquired five independent topographic images of the optic nerve head of eight normal eyes and eight eyes with primary open-angle glaucoma with a laser tomographic scanner. Each image had a field of view of 15 x 15 degrees with a resolution of 256 x 256 pixels. The pixel size was approximately 15 x 15 microns. The value of a pixel of a topographic image represented the height at this position. The mean height and the standard deviation over the five topographic images were calculated for each of the 65,536 pixel positions. The standard deviation of a single height measurement in normal eyes was 38.7 microns (range, 23.4 to 62.2 microns) for areas in the peripapillary retina and 42.6 microns (range, 24.4 to 53.7 microns) for measurements within the optic nerve head area. In glaucomatous eyes, the standard deviation was 41.2 microns (range, 23.2 to 59.6 microns) in the peripapillary retina and 49.4 microns (range, 28.1 to 72.8 microns) within the optic nerve head. There was no significant difference between the standard deviation of a single height measurement in normal and glaucomatous eyes (P = .34 within the optic nerve head area; P = .57 on peripapillary retina). No correlation was found between standard deviation of the measurements and pupil size or age of the subject.

Adult↗
PubMed1991

Accuracy of topographic measurements in a model eye with the laser tomographic scanner.

The authors evaluated the accuracy of topographic measurements with the laser tomographic scanner using a model eye. Diameter, depth, and shape at different axial lengths of four sample holes that simulated optic nerve heads in phakic and aphakic conditions were determined by confocal imaging. The computer-generated cross-section profiles of the simulated optic nerve heads corresponded well with the actual contours as photographed by scanning electron microscopy. The average relative error in diameter was 2.0% (range: 0.3-2.9%) for the phakic model eye and 3.6% (range: 0.6-8.2%) for the aphakic model eye. The average relative error in depth was 11.7% (range: 1.2-20.1%) for the phakic model eye and 10.1% (range: 1.7-22.6%) for the aphakic model.

Eye↗
PubMed1990

Histopathologic validation of Fourier-ellipsometry measurements of retinal nerve fiber layer thickness.

We describe a new technique for the measurement of retinal nerve fiber layer thickness and compare its results with histopathologic measurements in the same eyes. For these studies, two fixed monkey eyes were incised and placed on a pedestal in a plastic viewing dish. The eyes were perfused to maintain a pressure between 10 and 20 mm Hg. An ellipsometer, an optical device used to measure the change in polarization of light (retardation), was implemented in a laser tomographic scanner to obtain polarization data from the two monkey retinas. For the 15 measured locations, retardation ranged between a mean (+/- SD) of 0.9 degrees +/- 1.8 degrees and 23.7 degrees +/- 0.3 degrees. Subsequently, retinal nerve fiber layer thickness was measured at the imaged points in epoxy resin-embedded sections by an observer masked to the ellipsometry data. These values ranged between 20.4 microns and 213.9 microns. There was an excellent correlation (R = .83) between retardation and the histopathologic measurement of retinal nerve fiber layer thickness. Quantitating retinal nerve fiber layer thickness may enhance discrimination between glaucomatous and normal eyes earlier than is currently available by anatomic and functional approaches.

Animals↗
PubMed1989

Confocal laser tomographic analysis of the retina in eyes with macular hole formation and other focal macular diseases.

To study the retinal surface in the human eye in normal and diseased states we used laser scanning tomography. The confocal arrangement of the laser tomographic scanner permits examination of retinal topography in the axis perpendicular to the retinal surface. The eyes examined with the laser tomographic scanner included normal eyes, eyes with macular holes, impending macular holes, radiation retinopathy, macular edema, photocoagulation scars, subfoveal scars, and serous detachment of the fovea associated with subretinal neovascularization. The laser tomographic scanner is a new method that allows measurements of the topography of the internal limiting membrane in the macular area and may improve our understanding of the pathophysiologic characteristics and treatment of a variety of disorders of the macula.

Adult↗
PubMed1989

The effect of increased intraocular pressure on visual acuity and corneal curvature after radial keratotomy.

To detect the effect of increased intraocular pressure on visual acuity and corneal curvature after radial keratotomy, we measured these variables in the sitting and inverted positions in 18 patients who underwent radial keratotomy (Group 1) and compared their results with those from the unoperated on eyes of seven patients (Group 2). We also compared the results before and after inversion within each group. Intraocular pressure increased to approximately two times normal in each group. Significant improvement in visual acuity and reduction in central keratometry were noted only in Group 1. By multiple regression analysis, visual improvement correlated with the number of incisions but not the time since surgery. Our study provides evidence that increased intraocular pressure may account for transient changes in vision and corneal curvature after radial keratotomy.

Adult↗
PubMed1989

The effect of pterygia on contrast sensitivity and glare disability.

To detect subtle changes in visual acuity, we measured spatial contrast sensitivity in 12 patients with pterygium (Group 1) and compared their results with those from an age- and sex-matched control population (Group 2). Glare disability was also measured in each group. Measurements of contrast sensitivity were lower in Group 1 at all spatial frequencies than those of Group 2, independent of the testing device used. Glare disability was significantly increased in Group 1 compared to Group 2. Our studies indicate that contrast sensitivity and glare disability testing may provide additional objective methods for documenting impaired vision in patients with pterygium when Snellen visual acuity is minimally affected.

Adult↗
PubMed1989

Quantitative assessment of the optic nerve head with the laser tomographic scanner.

We describe the use of a laser tomographic scanner to objectively measure optic nerve head topography. A laser beam is focused on the optic disc using confocal imaging. Reflected light is detected only if it originates from a small region around the focal place of the special optics. Optic disc parameters are calculated from the measured values of confocal reflected light. In five glaucomatous eyes, maximum cup depth was between 0.33 mm and 0.58 mm. Cup volume was between 0.10 mm3 and 0.65 mm3; it correlated well with ophthalmoscopy. Compared with conventional imaging systems, the laser tomographic scanner has certain advantages: 1) images can be obtained with miotic pupils; 2) clarity of media is not important; 3) low light intensity is employed; and 4) a real time image is obtained.

Eye↗