Biomedical subjects

R O Burk

Publications and source records attributed to R O Burk.

36 records · Page 2Linked to original sources

PubMed1994

Reproducibility of the optic nerve head topography with a new laser tomographic scanning device.

BACKGROUND: Laser scanning tomography has been shown to be an accurate and reliable method for the assessment of the three-dimensional optic disc topography. The authors investigate the reliability of morphometric measurements with the Heidelberg retina tomograph, a new instrument which was designed based on this technology, which simplifies handling and is much smaller than the laser tomographic scanner. METHODS: Three independent measurements of the optic disc were performed in 39 eyes of 39 patients which were equally divided into the following three groups: glaucoma, glaucoma suspects, and controls. RESULTS: The mean coefficient of variation for measurement in the glaucoma, glaucoma suspect, and control groups was 2.9%, 5.0%, and 3.4%, respectively, for cup area; 4.9%, 4.6%, and 4.6%, respectively, for cup volume; 5.2%, 3.8% and 3.3%, respectively, for mean cup depth; and 5.2%, 4.1%, and 4.0%, respectively, for maximal cup depth. The mean standard deviation for one pixel of the total image was 30 +/- 6 microns, 28 +/- 7 microns, and 22 +/- 6 microns for the three groups, respectively. CONCLUSION: The Heidelberg retina tomograph enables fast and reliable measurement of the optic disc topography and therefore may allow exact follow-up of patients.

Adult↗

PubMed1994

[3-dimensional topography of the optic papilla with laser scanning tomography: clinical correlation of cluster analysis].

BACKGROUND The evaluation of optic disc topography is essential for the clinical diagnosis of primary open angle glaucoma. The purpose of this study was (1) to establish a computerized cluster formation of optic nerve head topography based on quantitative three-dimensional parameter values and (2) to describe the resulting clusters according to morphological appearance and visual fields. PATIENTS AND METHODS 337 optic nerve heads (glaucomatous optic neuropathy (n = 99), glaucoma suspects (n = 159), normals (n = 79) were analyzed using laser scanning tomography. A hierarchical cluster analysis was performed based on standardized variables (optic disc area, rim area, area-ratio, cup depth, cup steepness, height variations along the contour-line). Visual fields were tested by computerized static threshold perimetry. RESULTS A seven cluster solution met the optimizing criteria. The characteristic morphology of the clusters can be described as "normal" (N), "normal, large" (NL), "supernormal" (SN), "pseudonormal" (PN), "glaucoma-like-flat" (GF), "glaucoma-like-steep" (GS) and "macropapillary" (M). Visual fields were normal in 180 eyes. 99 eyes had glaucomatous field defects, 58 eyes revealed isolated relative scotomas < 10 db. Presence and degree of visual field defects varied within the automatically classified optic disc groups considerably. Visual field defects were found in 7.7% (SN), 8.3% (N), 18.8% (NL), 33.3% (M), 37% (PN), 64.7% (GF) and 83.3% (GS) respectively. Pseudonormal discs were characterized by a flattening of the height variations along the disc border. CONCLUSIONS (1) Optic nerve heads may be automatically classified based upon a combination of three-dimensional topographic variables. (2) Analysis of optic disc topography and computerized perimetry are supplementary tools in the evaluation of the glaucoma patient. Visual field defects may be present within any cluster. However, the likelyness of the presence of visual field defects differs considerably among the topometrically defined groups of optic nerve heads. Functional damage is to be expected in association with reduced height variations along the disc border, a small rim area and a steep cupping of the optic nerve head.

Cluster Analysis↗

PubMed1994

[Follow-up examinations of papillary morphology with laser scanning tomography].

UNLABELLED: The object of this study was to investigate the perceptibility of changes in the topography of the optic nerve head during follow up with laser scanning tomography (LST), with a minimum observation period of 24 months. METHODS: We evaluated the changes in cup and rim area, cup volume, and mean and maximum cup depth in 50 eyes (8 control eyes, 21 glaucomatous eyes, 21 eyes in which glaucoma was suspected by LST over a mean follow-up time of 36 +/- 10 (range 24-49) months and compared them with the results of computerized static perimetry (Octopus). Changes were considered to be significant if they were larger than three times the maximum deviation measured in one parameter and larger than the maximum deviation in one other parameter [27]. RESULTS: Among 10 eyes that showed increasing cup values, 5 initially presented with striking disc cups, and no pathologic function tests; in none of these eyes was functional loss revealed by perimetry during the follow-up period. Of the 5 glaucomatous eyes in which progression was found on optic disc morphometry, 4 had increasing defects revealed by computerized static perimetry (Octopus 500). CONCLUSION: The results confirm the value of LST. In 6 eyes in which LST revealed a significant increase in the optic cup values, perimetry did not demonstrate progression of the functional loss. Therefore, LST should be used in the follow up of all patients with glaucoma or suspected glaucoma, in addition to conventional computerized perimetry.

Adult↗

PubMed1993

Laser scanning tomography and stereophotogrammetry in three-dimensional optic disc analysis.

Laser scanning tomography (LST) and computed stereophotogrammetry (CSP) are sophisticated diagnostic tools for the three-dimensional analysis of optic nerve head topography. The two methods are based on different physical principles. To compare the information about the shape of the cup of an optic nerve head obtained by LST and CSP, we evaluated the volume profile (VP; i.e., the cross-sectional area of the cup from top to bottom) in 36 discs of 36 patients (20 control group discs C, 16 glaucoma discs G). The Spearman correlation coefficient between the photogrammetric and the laser scanning VP-slope measurements was rs = 0.931; P < 0.001 (rs = 0.935 G, P < 0.001; rs = 0.910 C, P < 0.001). The results suggest that confocal laser scanning provides readings of the shape of the optic disc cup that are similar to the measurements of computed stereophotogrammetry.

Adolescent↗

PubMed1993

Reproducibility of topometric data acquisition in normal and glaucomatous optic nerve heads with the laser tomographic scanner.

The reproducibility of optic disc cup measurements was analyzed in 24 eyes of 24 patients [8 normals, 8 glaucoma patients, 8 glaucoma suspects] using the Laser Tomographic Scanner. The mean coefficient of variation in triple measurements was 5.0% for the cup area, 5.4% for the rim area, 7.0% for the cup volume, 4.0% for the mean cup depth, and 4.3% for the maximum cup depth. Mean reliability between two of the three measurements performed in each eye was better than 0.988 for the cup area, 0.995 for the cup volume and 0.996 for the mean cup depth readings. These results suggest that laser scanning tomography allows highly reproducible measurements in living eyes and adds an important tool to the ophthalmologist's armamentarium for the diagnosis and follow-up of glaucoma patients.

Female↗

PubMed1993

[Melanoma of the iris with recurrent hyphema--course over 32 years].

BACKGROUND: The differential diagnosis of melanocytic iris tumours is very difficult. Signs of malignancy such as pupil distortion, ectropium uveae, secondary cataract and secondary glaucoma can also occur with benign iris nevi. However, spontaneous hyphemata occur in 6.9% to 13% of melanomas, while anterior chamber hemorrhages are extremely rare with nevi. PATIENT AND METHOD: A 69 year old man with a pigmented iris tumor of the right eye strictly refused surgical treatment. Therefore the tumor was followed clinically over 32 years. Over this period the tumor showed a very slow increase in size. Twenty-seven years after the initial presentation for the first time a spontaneous anterior chamber hemorrhage occurred. In the following period, the patient experienced recurrent hyphemata at last approximately every two months. An excisional biopsy consisting of a sector-iridectomy and localized excision of Descemet's membrane was performed. Histologically, the tumor was classified as a melanoma of the iris. CONCLUSION: A careful documentation cannot be overemphasized in the follow up of patients with pigmented iris lesions. In case of spontaneous hyphema histological evaluation is required even in the absence of evident tumor growth.

Aged↗

PubMed1993

[Determination of retinal nerve fiber density in vivo using laser polarimetry].

BACKGROUND: A direct in vivo measurement of the retinal nerve fiber layer thickness enables new possibilities for the detection of nerve fiber defects. Using the principle of polarimetry the Nerve Fiber Analyzer has been told to measure directly the nerve fiber layer thickness in vivo. PATIENTS AND METHODS: We measured the nerve fiber layer thickness along a peripapillary circle and investigated the reproducibility in 10 independent measurements of 10 left eyes of ten normals. RESULTS: The nerve fiber layer thickness measurements varied between 10 and 130 microns for single pixel measurements. The coefficient of variation was 11.9 +/- 2.6 percent for a peripapillary circle while the temporal, nasal, superior and inferior quandrants were 19.2 +/- 3.6%, 19.5 +/- 4.7, 14.3 +/- 5.6 and 16.4 +/- 5.5 percent, respectively. Mean coefficient of variation in 10 time evaluation of 5 single examinations of 5 different eyes was 1.8 +/- 1.1%. CONCLUSIONS: The first investigations demonstrate a good reproducibility of the measurements observed by the Nerve Fiber Analyzer. Supplementary to three-dimensional optic disc topography and perimetry, nerve fiber layer thickness assessment may become an additional tool for diagnosis and follow-up of early glaucoma. The option of measuring along circle segments or areas instead a peripapillary circle consisting of a single pixel would increase the clinical value and reproducibility. Further studies are warranted to evaluate the accuracy of this new method of polarimetry.

Equipment Design↗

PubMed1993

[Bilateral acanthamoeba keratitis].

BACKGROUND: Given the protracted clinical course, diagnostic difficulties, frequent treatment failures and the increasing incidence, keratitis caused by free-living acanthamoeba represents a clinical challenge. PATIENT AND METHODS: A 37-year-old healthy female who wore gas-permeable contact lenses for ten years developed bilateral keratouveitis, pseudodentritic subepithelial infiltrates and corneal ring ulcers. Cultures were obtained from corneal scrapings, contact lenses and storage container. Medical treatment during the clinical course included propamidine isethionate, miconazole, ketoconazole, polymyxin B, aminoglycoside antibiotics and corticosteroids. Surgical procedures included bilateral penetrating keratoplasty and extracapsular cataract extraction. Each corneal button was examined after chemofluorescent staining with calcofluor white. RESULTS: Klebsiella oxytoca and Serratia marcescens were grown from cultures of the contact lens storage container. Although suspected early in the clinical course repeated cultures from corneal scrapings were negative for acanthamoeba. Despite transient remission, medical therapy including therapy for acanthamoeba could not halt the progression of infection in both eyes. Visual acuity deteriorated to light perception and counting fingers, respectively. Penetrating keratoplasty was performed 12 and 15 months after the onset of symptoms. Histopathological examination allowed identification of acanthamoeba cysts in each button. Because of secondary cataract formation cataract-extraction with intraocular lens implantation was simultaneously performed in the right and subsequently in the left eye. While corneal infiltrates recurred and optic atrophy developed due to secondary glaucoma in the right eye, the left corneal graft has remained clear. CONCLUSIONS: The case-report demonstrates that diagnostic procedures may fail to detect acanthamoeba organisms before obtaining a corneal button for histopathologic examination. Decreased corneal sensation later in the clinical course after initial pain disproportionately related to clinical signs does not exclude the diagnosis of an acanthamoeba keratitis. Medical treatment failure may occur despite early initiation of antiparasitic therapy.

Acanthamoeba Keratitis↗

PubMed1993

[Comparison of two laser scanning tomography systems for three-dimensional analysis of the optic papilla].

The Heidelberg retina tomograph (HRT) allows three-dimensional topographic analysis of the optic disc based on the same confocal laser tomographic scanning principle as the laser tomographic scanner (LTS). We evaluated the reproducibility attained with the HRT and compared the data acquired with the two instruments. To determine the reproducibility of the data acquisition with the HRT, we measured 27 glaucomatous discs five times each. The mean standard deviation was 0.075 mm2 for the cup area, 0.035 mm3 for the cup volume and 0.018 mm for the mean cup depth. In addition, 50 eyes were examined with both instruments. Measurements of the optic disc area and cup area demonstrated slightly increased values obtained with the HRT (mean difference 4.1% and 6.6%, respectively), while the values for cup volume and cup depth were 15.5% and 13.9% larger than those obtained with the LTS. The comparison between LTS and HRT demonstrates good agreement of the reproducibility concerning three-dimensional topometric data relating to the optic nerve head. The differences between the measurements may be due to a modified optical pathway enabling direct assessment of the intraocular focus position in the HRT. In conclusion, the improved and simplified method of laser scanning tomography as used in the HRT yields reproducible and reliable measurements of the optic nerve head. In addition, this instrument makes it possible to obtain high-quality images without pupil dilatation with a significantly shorter examination time.

Equipment Design↗

PubMed1992

Are large optic nerve heads susceptible to glaucomatous damage at normal intraocular pressure? A three-dimensional study by laser scanning tomography.

To evaluate the effects of the presence of glaucomatous visual field defects and of intraocular pressure elevations on optic nerve head topography, we analyzed 148 left optic nerve heads of 148 patients using laser scanning tomography. The optic discs are classified according to computerized static perimetry and documented IOP readings: 101 discs show normal visual fields (36 normal discs, 22 ocular hypertensives, 28 normotensive glaucoma suspects and 15 ocular hypertensive glaucoma suspects), 47 discs (34 high-pressure glaucoma discs, 13 normal-tension glaucoma discs) demonstrate glaucomatous visual field damage. A two-way analysis of variance discloses significant differences (P < 0.01) between the groups of optic discs classified according to perimetry for most topometric parameters evaluated except for disc area. Classification according to documented IOP (cut off at 21 mmHg) results in larger disc areas in normotensive discs compared to hypertensive optic nerve heads in the study population. Results suggest that large discs may be susceptible to glaucomatous visual field damage at statistically normal IOP readings.

Adult↗

PubMed1992

[3-dimensional topographic analysis of the papilla as a component of glaucoma diagnosis].

Three-dimensional topography of the optic nerve head can be objectively described by means of quantitative parameter values. Owing to interindividual variability in the disc configuration, new structural variables, such as the relative height of the peripapillary retinal nerve fiber layer in stereo-videography and height variations in the contour line along the disc border in laser scanning tomography, have been shown to differentiate normal optic discs and optic nerve heads with pathological alterations better than standard volumetric data. Using laser scanning tomography, the effect of age on the parameter values of disc area, rim area and the ratio of the cup-to-disc area was evaluated in 61 healthy subjects (age 14 to 77) who had normal visual fields on computerized static perimetry. The rim area decreased with age (rs = -0.26, P < 0.05); the ratio of the cup area to disc area increased (rs = 0.25; P < 0.05). No relationship was found between patient age and disc area (Spearman correlation). Although the coefficients of correlation are rather small, they may reflect the physiological age-related decline in axonal count. The high resolution of strictly confocal laser scanning microscopy allows for visualization of nerve fiber bundle defects underneath a surface of regular reflectivity. The existence of such hidden nerve fiber bundle defects has been postulated before on the basis of experimental studies and may be an early morphological sign of glaucomatous damage.

Glaucoma↗

PubMed1992

Depth position of spontaneous venous pulsations in ocular hypertensives and control-group discs.

Spontaneous venous pulsation can be observed at the site of entry of retinal veins into the physiological cup of the optic disc. Although it has been speculated that spontaneous vessel pulsation is related to primary open-angle glaucoma, no evaluation has been done on the depth position of such a pulsation inside the cup and its relationship to the intraocular pressure. Using laser scanning tomography, we measured the depth position of the maximal spontaneous vessel pulsation inside the optic cup in 24 discs of 24 patients, including 15 ocular hypertensives and 9 controls. The two groups did not differ significantly in age or refraction. The depth position of the maximal venous collapse, however, showed a significant difference between the two groups (p < 0.005), the mean value being 301 +/- 95 microns beyond the first retinal vessel reflection in the control-group eyes and 507 +/- 193 microns in the ocular hypertensive discs. The location of the depth position of the maximal venous collapse within the excavation could be a parameter that indicates the individual pressure tolerance of the ocular tissues.

Adult↗

PubMed1991

[Volumetric analysis of the optic papilla using laser scanning tomography. Parameter definition and comparison of glaucoma and control papilla].

We performed a three-dimensional structure analysis of the optic disc in 65 eyes of 65 patients (38 glaucoma patients, 27 control-group patients) using laser scanning tomography. Patients classified as glaucoma showed at least 3 points with a relative scotoma of -10 db loss or greater compared to age matched controls on static 30 degrees computerized perimetry. Control-group patients showed no relative scotoma outside the blind spot area compared to age matched controls. One way analysis of variance revealed statistically significant differences between the glaucoma (G) and the control-group (C) for excavation volume (+0.57 +/- 0.37 mm3 G/0.31 +/- 0.27 mm3 C, p less than 0.01), for the 3rd moment of the frequency distribution of excavation depths readings (-0.01 +/- -0.12 G/-0.13 +/- -0.09 C, p less than 0.001), area ratio (0.75 +/- 0.15 G/0.57 +/- 0.16 C, p less than 0.001), depth area ratio (0.35 +/- 0.24 G/0.18 +/- 0.12 C, p less than 0.001). A stepwise discriminant analysis classified 32 of 38 (84.2%) glaucoma discs and 21 of 27 (77.8%) control-group discs by a linear combination of 5 out of 15 topographic parameters. The results suggest that a combination of topographic parameters may provide an objective optic disc classification.

Computer Graphics↗

PubMed1991

[Capillary hemangioma of the retina. Laser scanning tomography follow-up after radiotherapy].

We present a patient with isolated angiomatosis retinae, in whom ruthenium irradiation was administered for treatment of a secondary serous retinal detachment. Prior to therapy, we measured an increased vessel diameter. Following treatment, decreasing venous vessel diameter was documented three-dimensionally utilizing laser scanning tomography. The changes in vessel height (87%) exceeded the changes in width (49%). This is most probably because the vessels are embedded in the nerve fiber layer, stabilized by the surrounding tissues more in a horizontal than in a vertical direction. In addition, spontaneous venous pulsation located in the optic disc and in the retina was documented.

Adult↗

PubMed1990

[Papilledema. Follow-up using laser scanning tomography].

Normally, the elevation of optic disk swelling is measured by ophthalmoscopy. Laser scanning tomography (LST) permits three-dimensional analysis of distinct intraocular structures under in vivo conditions with high accuracy. We present a case of papillitis, in which the elevation could be determined as 550 microns, leading to a volume of 1.48 mm3, increasing to an elevation of 870 microns and a volume of 1.72 mm3 11 days later. Clinically, we found a swelling of about 1 D in the first examination, increasing to 2 D at the maximum. Six weeks later there was only a distinct temporal pallor to be seen, while the LST showed us an elevation of 190 microns (volume 0.22 mm3).

Adult↗

PubMed1989

Reproducibility of topographic measurements of the optic nerve head with laser tomographic scanning.

Topographic analysis and measurement of the optic nerve head is important for the diagnosis and follow-up of glaucoma. To quantify structures of the optic nerve head the new technique of laser tomographic scanning was used. A laser beam was focused onto the surface of the optic nerve head and the reflected light was detected in a confocal detection unit. The consequent change of focus produced a tomographic scanning series and allowed measurement of three-dimensional structures. To analyze the reproducibility of optic cup measurements the authors did ten recordings of one eye of eight normal volunteers. The mean standard deviation of the measurements was +/- 0.015 mm3 and the mean coefficient of variation was 9.5%. Confocal laser tomographic scanning is a safe, effective, convenient method to measure and document the topography of the optic nerve head and should be a valuable technique for follow-up of glaucoma patients.

Humans↗

PubMed1989

[3-dimensional biomorphometry of the papilla using a laser tomography scanning procedure--initial experiences with pathologic papillar findings].

Three-dimensional topographical analysis of the optic nerve head and the parapapillary region was performed with a confocal laser tomographic scanner. Four patients with various disorders of the optic nerve head (glaucoma, optic disk pit, morning glory syndrome and a parapapillary neoplasm) were investigated as examples of application of the method in a clinical setting.

Adult↗

PubMed1989

[Mesectodermal leiomyoma of the ciliary body--clinical aspects, surgery and immunohistochemistry].

The clinical, surgical and light microscopical features of a mesectodermal leiomyoma of the ciliary body are presented. Slit-lamp examination of a 63-year old woman strongly suggested a malignant lesion of the ciliary body and the peripheral choroid. Following cryoretinopexy and argonlaser-photocoagulation, the tumor and the adjacent portion of the cornea, angle structures, iris, ciliary body, choroid and sclera were removed en bloc. The defect was covered by a corneosclerotransplant 14 mm in diameter. Histological examination revealed a well circumscribed tumor of the ciliary body, consisting of sheets of fusiform cells. Intracytoplasmatic filaments gave a positive reaction to an actin antibody (Actin HHF 35 MA 931), demonstrating the smooth muscle origin of the ciliary body tumor by immunocytochemical means.

Biomarkers, Tumor↗