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Biomedical subjects

K Heimann

Publications and source records attributed to K Heimann.

At least 109 records · Page 6Linked to original sources
PubMed1995

Posterior drainage of intraocular fluid: an experimental approach on bovine cadaver eyes.

We evaluated the posterior drainage of saline in cadaver bovine eyes using different experimental procedures. The saline perfusion via a pars plana infusion into the vitreous cavity was measured in the following 5 different groups of 20 enucleated bovine eyes: 1, control; 2, vitrectomy; 3, vitrectomy + retinectomy; 4, vitrectomy + retinectomy + removal of retinal pigment epithelium (RPE); and 5, vitrectomy + retinectomy + removal of RPE + choroidectomy. The mean values obtained for the facility of saline outflow were as follows group 1, 0.0458 microliter min-1 mmHg-1; group 2, 0.0393 microliter min-1; group 3, 0.1308 microliter min-1 mmHg-1; group 4, 0.2288 microliter min-1; and group 5, 0.9985 microliter/min-1 mmHg-1. The retina appeared to be the major barrier to fluid movement from the vitreous to the chorioid, perhaps due to the lack of extracellular space and to the tight and impervious structure of the retina. The barrier function of the retina may explain the hypotony seen after rhegmatogenous retinal detachment and the decrease in intraocular pressure observed after the removal of silicone oil in eyes that had undergone retinectomy. Our results suggest that the reduction in intraocular pressure occurring after retinectomy is attributable to the new drainage pathway.

Animals↗
PubMed1994

Immune response to specific molecules of the retina in proliferative vitreoretinal disorders.

In recent years, several reports have contributed to a growing suspicion that there is immunologic involvement in proliferative intraocular disorders such as proliferative vitreoretinopathy and proliferative diabetic retinopathy. Immune privilege, as in the brain, ovary and testis, also exists in the eye. Therefore, immune responses to unique molecules of the eye, e.g. retinal S-antigen (S-Ag), which the immune system never learns to regard as "self", are possible. This study describes the presence of S-Ag, a major soluble photoreceptor protein involved in the visual transduction cascade, in pathological vitreous. We employed indirect immunoblotting, with human retina as substrate, and demonstrated the occurrence of antiretinal antibodies in the sera of a series of patients with proliferative vitreoretinal disorders. Immunoblot analysis of physiological retina and lyophilized S-Ag, revealed this protein as a target molecule of the immunological involvement of the retina. Further immunochemical investigation, however, must clarify whether this autoimmune reaction is the cause, a consequence, or an aggravating factor of the disease. As we come to understand the cellular and molecular mechanism, a new generation of therapeutic strategies may be envisioned.

Antigens↗
PubMed1994

The significance of vitronectin in proliferative diabetic retinopathy.

Vitronectin, an integrin-binding a-1-glycoprotein with potent cell-adhesion and proliferation-mediating properties, has been shown to be incorporated in surgically removed membranes from patients with proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR) and macular pucker. Therefore we developed an ELISA technique to quantify levels of vitronectin in human vitreous and plasma samples in order to be able to evaluate the significance of vitronectin in these different vitreoretinal diseases. Our results indicate a significant increase of vitronectin in all proliferative disorders except idiopathic macular pucker. Adjustment of all probes to equal total protein content yielded a significant increase only in PDR (type II diabetes). Plasma samples demonstrated a significant increase of vitronectin in patients with type II diabetes suffering from PDR. Therefore, break-down of the blood-retina barrier appears to be the most likely explanation for the increased levels of vitronectin in the vitreous. Our results indicate that vitronectin may not only be involved in the regulation of epiretinal membrane formation at significantly higher levels in patients with type II diabetes, but the increase of vitronectin in diabetic plasma may also help to explain the pathological alteration of the coagulation cascade in diabetics.

Blotting, Western↗
PubMed1994

Visual outcome of secondary lens implantation after trauma or complicated retinal detachment surgery.

PURPOSE: Visual outcome of intraocular lens (IOL) implantation as a separate surgical procedure after severe trauma of the anterior or posterior segment or after vitreoretinal surgery for complicated retinal detachment resulting in aphakia was evaluated. METHODS: The charts of all patients undergoing secondary IOL implantation for the above reasons between 1988 and 1992 were retrospectively reviewed. A special transcleral suturing technique was developed for the posterior chamber lenses, where needles are primarily passed from the outside through the sclera to enhance correct positioning of the sutures. RESULTS: In all but one of the cases in group 1, visual acuity after surgery was equal to or better than before surgery. In the second group, visual acuity after surgery was equal to or better than before surgery in 9 of 12 cases. CONCLUSIONS: Secondary IOL implantation after severe trauma or vitreoretinal surgery for complicated retinal detachment is a fairly safe technique, with only few transient complications. Visual acuity did not deteriorate after surgery by more than two lines in any the cases discussed. Peripheral binocularity was restored in all cases. The suturing technique described here, in which the needles are primarily passed from the outside through the sclera, offers the advantage of exact positioning of the haptics in the ciliary sulcus.

Adolescent↗
PubMed1994

Histopathologic study of epiretinal proliferations after vitrectomy with daunomycin and silicone oil.

PURPOSE: The cellular composition of primary and recurrent periretinal proliferations has been widely described. The use of daunomycin, an antiproliferative antibiotic, has been recommended to reduce these proliferations. Two recurrent membranes after intraoperative application of daunomycin were examined. METHODS: Two epiretinal membranes, which were removed 5 months and 20 months after vitrectomy with daunomycin, were examined by light and electron microscopy to determine the structure and cellular composition of these membranes. RESULTS: The matrix of the membranes consisted of new collagen with fiber diameters between 20 and 22 nm. Fibrocytes and macrophages were present in both specimens. Retinal pigment epithelial cells and fibrous astrocytes were present in only one specimen. CONCLUSION: Retinal pigment epithelial cells, which are consistently present in primary periretinal membranes, were found in only one of the two specimens examined. Myofibroblasts, also normally present, were not found. The other cells found are typically seen in primary periretinal proliferations.

Adult↗
PubMed1994

[Protein composition of the vitreous body in proliferative diabetic retinopathy. An analysis with 2-D-electrophoresis].

Gradient SDS-polyacrylamide gel electrophoresis is a useful technique for characterization of soluble human vitreous protein. However, this technique is limited in the case of suboptimal discrimination power. In this study, we used 2-D electrophoresis to analyse the protein composition of proliferative diabetic retinopathy (PDR) intraocular fluid (n = 10), and compared it with normal vitreous (n = 10) and serum (n = 10). In normal vitreous, the protein content consisted mainly of albumin, transferrin, alpha 1-antitrypsin, IgG, and prealbumin as confirmed by the comparison with protein standards. Compared to vitreous controls, all PDR samples were shown to have lower amounts of transferrin, alpha 1-antitrypsin, and prealbumin. However, the amounts of IgG were higher than in the controls. This reflects a shift to a serum-like protein profile, indicating a blood-retinal barrier breakdown. However, we also detected in PDR vitreous three protein spots in a low-molecular-weight range (5-10 kDa) none of which could be found in native vitreous or in serum. Therefore, additional local protein synthesis appears to be present in the pathogenesis of PDR. 2-D electrophoresis permits precise characterization of the soluble vitreous proteins which may be associated with the fibrovascular proliferative vitreoretinal response.

Blood Proteins↗
PubMed1994

Validity of two-dimensional data obtained with the Heidelberg Retina Tomograph as verified by direct measurements in normal optic nerve heads.

The Heidelberg Retina Tomograph (HRT) was recently developed to measure two- and three-dimensional parameters of the optic disc. The instrument gives measurement results on an absolute scale; the validity of the scaling has never been proven in the living eye. Eight phakic eyes (eight patients) scheduled for subsequent pars plana vitrectomy were selected for this study. The optic disc was scanned using the HRT. During vitrectomy, the disc was measured directly using a modified retina spatula that had a 2.5-mm scale with a grading of 1/10 mm at the tip. The measurement was recorded with a high-resolution video system adapted to a Zeiss operation microscope. We used a vitrectomy contact lens with a flat surface. First we looked for reference points along the disc margin that could be clearly identified on both images, then we determined the distances between these points. Calculations from HRT data followed according to the software used in this instrument. Calculations from video images were related to the grading of the intraocular scale instrument. As determined using HRT software version 1.08, the mean ratio of HRT distances obtained by direct video measurements was 1.031 (SD, +/- 0.099; SE, +/- 0.035). No significant correlation between the ratio and the ametropia of the eyes could be verified (r = 0.506, P = 0.20). On average, the two-dimensional measurements of the HRT were correct. Furthermore, we used software version 1.07, which does not correct the image size depending on refraction, and found that the mean ratio of HRT distances obtained direct video measurements was 0.985 (SD, +/- 0.108; SE, +/- 0.038).(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1994

Atypical presentations of Best's vitelliform macular degeneration: clinical findings in seven cases.

The clinical findings obtained in seven patients from four families with atypical vitelliform macular degeneration are described. Five patients had an onset of the disease in childhood and two patients, at the age of 45 years. Their visual acuity was mildly reduced (0.52 +/- 0.27). The fundus showed variable changes with single or multiple central or paracentral yellowish subretinal exudates and deposits, sometimes surrounded by scars. Both eyes were affected in all patients. The scotopic and photopic electroretinograms were normal in all cases. The electrooculogram (EOG) showed a significant reduction of the light rise in all affected eyes, and in five eyes a reduction in the dark trough could be observed. In three clinically unaffected first-order relatives with normal fundus appearance, the light rise of the EOG was reduced, thus identifying them as gene carriers. The clinical features of atypical vitelliform macular degeneration are discussed with respect to similar diseases that must be excluded and may give reason for misdiagnosis.

Child↗
PubMed1994

Anterior proliferative vitreoretinopathy in trauma and complicated retinal detachment. A histopathologic study.

Anterior vitreoretinal proliferations are frequent sequelae of retinal detachment repair and severe trauma. Cellular proliferations can form membranes extending anteriorly from the peripheral retina. These membranes have the capability to contract and may lead to detachment of both the peripheral retina and, in more advanced stages, the ciliary body. Because the vitreous base and vitreous remnants are leading structures for cellular proliferation, complete removal of the anterior vitreous base in particular is important in cases of severe trauma or complicated retinal detachment. In 11 cases of anterior proliferative vitreoretinopathy examined histopathologically, we found overlying membranes and cellular infiltration of the vitreous in close correlation with the amounts of vitreous remnants present. Visualization of the peripheral retina and pars plana can rarely be accomplished in the presence of the crystalline lens or pseudophakia. Therefore, the removal of the anterior vitreous is often incomplete. To achieve complete dissection of the anterior vitreous, we remove even a clear lens during the first surgical intervention in selected cases.

Adult↗
PubMed1994

Reconstruction of the anterior and posterior segment of the eye after massive injury.

We treated 15 patients whose common characteristic was a severe windscreen injury (7 eyes) or an (mine) explosion trauma (8 eyes), nearly always affecting both eyes. In several operations we tried to reconstruct the anterior and posterior segments using a temporary keratoprosthesis for repair of the posterior-segment damage. In cases where the retina could be attached, the initial result was a functional stabilization and improvement. In 4 eyes we implanted an artificial iris diaphragm to prevent silicone-corneal contact. The long-term results will depend on the functionality of the ciliary body.

Accidents, Traffic↗
PubMed1993

Repair of outer blood-retinal barrier after severe ocular blunt trauma in rabbits.

Retinal contusion is a leading cause of visual loss in ocular blunt trauma. However, its pathogenesis remains controversial. We established a rabbit model of severe retinal contusion with energy of about 2.87 J. Typical retinal edema and sometimes subretinal hemorrhage reproducibly occurred at the posterior pole after injury. These subsided 1 week later with depigmentation in the lesion. Histopathological examination revealed severe damage of the outer layer of retina, for example, disruption of retinal pigment epithelium (RPE) and photoreceptors. Electroretinography showed a decrease in the b wave by 38-47% in amplitudes (P < 0.01) during the first 3 days and then returned, although not to normal level. To investigate the damage and repair of blood-retinal barrier (BRB), 5 ml 2% lanthanum solution (La) was injected via the common carotid artery 1-2 min before enucleation. La diffused in the interphotoreceptor space through the damaged junctions of RPE 1 h-3 days after injury. La also reached the nuclei level of photoreceptors up to 14 days after injury. Although a glial scar with scattered RPE cells attached to Bruch's membrane in the severely damage area, no La diffusion was found in the retina 4 weeks after trauma. These results showed incomplete repair of outer BRB after severe blunt trauma.

Animals↗
PubMed1993

Corticosteroids and daunomycin in the prevention of experimental proliferative vitreoretinopathy induced by macrophages.

An experimental model of proliferative vitreoretinopathy (PVR) induced by macrophages simulates a special form of wound healing process in the eye and mimics the development of PVR from its initial stage. We used this model for the evaluation of drug efficacy in the prevention of PVR. One mg triamcinolone acetonide (TA), 10 micrograms daunomycin-liposome (DL), 5 micrograms free daunomycin (FD) and 0.1 ml saline or empty liposomes (as controls) were injected into the vitreous in four groups of animals (30 or 40 rabbit eyes each) after macrophage injection. Retinal detachment developed in 77.5% of the control eyes on day 28, compared to 13.3% of the TA-treated eyes (P < 0.01), to 33.3% of the eyes treated with DL (P < 0.01), and 50% of the FD-treated eyes (P < 0.05). TA cleared up from the vitreous within 35-63 days (average 45.5 days). The half-time of FD clearance was 145.5 min. Although DL declined rapidly during the first 2 days, there was an average of 0.64 microgram/ml daunomycin in the vitreous on day 14. Transmission electron microscopy showed that FD at a dosage of over 5 micrograms or DL over 20 micrograms was toxic to the retina and that up to 4 mg TA was nontoxic. These results suggest that steroids such as TA, given at the inflammatory stage, can effectively and safely prevent the development of PVR, and that encapsulation in liposomes of cytotoxic agents such as daunomycin can enhance drug efficacy and reduce toxicity. The time course of initiation and development of PVR is important in the selection of particular drugs.

Animals↗
PubMed1993

Detection of HIV in human vitreous.

Assay of human vitreous specimens obtained postmortem for HIV antibodies, or HIV p24 antigen, is reported to be a reliable technique to demonstrate HIV infection in possible cornea donors from whom serum could not be obtained. We tested three vitreous samples obtained during vitrectomy from two HIV-positive patients. One patient exhibited the clinical AIDS syndrome. HIV antigen and antibody tests were negative in all specimens. HIV proviral DNA was detected by PCR only in the vitreous of the patient with AIDS. Therefore, testing only vitreous samples is insufficient to exclude HIV infection in potential cornea donors.

Adult↗
PubMed1993

Macrophages in proliferative vitreoretinopathy and proliferative diabetic retinopathy: differentiation of subpopulations.

Macrophages have long been known to play a major role in the pathogenesis of proliferative vitreoretinal disorders. Using the monoclonal antibodies EBM11 (pan macrophage), 27E10 (early inflammatory stage marker), and RM3/1 (healing phase marker), different subpopulations of macrophages were differentiated in surgically removed membranes from patients with macular pucker (n = 6), proliferative vitreoretinopathy (PVR) following rhegmatogenous retinal detachment (n = 11), traumatic PVR (n = 19), and proliferative diabetic retinopathy (PDR) (n = 11). Macrophages were predominantly found in traumatic PVR and PDR. Some healing phase (RM3/1) macrophages were detected in all disease entities. Inflammatory stage macrophages (positive staining for 27E10) could not be detected in PVR following rhegmatogenous retinal detachment and idiopathic macular pucker. In traumatic PVR inflammatory stage macrophages were associated with a short history of disease whereas in PDR all types of macrophages could be detected regardless of clinical history and duration of the disease.

Antibodies, Monoclonal↗
PubMed1993

Origin of fibronectin in epiretinal membranes of proliferative vitreoretinopathy and proliferative diabetic retinopathy.

Fibronectins, high molecular multifunctional glycoproteins of the extracellular matrix and plasma, have been a popular area of research in the pathogenesis of proliferative disorders of the retina. Several immunohistochemical studies have revealed that fibronectin is a major constituent of epiretinal membranes and that the cell types involved in proliferative intraocular disorders may synthesise it. However, owing to the fact that plasma and cellular fibronectin are similar in their overall structure, the origin of fibronectin in epiretinal membranes has not yet been clearly defined. In this study, we used two monoclonal antibodies: FN-3, which recognises an extra domain present in the cellular but not plasma form of fibronectin; and FN-4, which reacts with an antigenic site on both plasma and cellular fibronectin. In 37 epiretinal membranes obtained from eyes with proliferative vitreoretinopathy and proliferative diabetic retinopathy, we demonstrated the presence of cellular fibronectin, thus indicating local production. The significantly stronger and positive immunostain with FN-4 in the same specimens suggests the colocalisation of plasma fibronectin, that may be derived from the breakdown of the blood-retinal barrier and trapped in membranes during their formation. In pathological vitreous we demonstrated both types of fibronectin by western blot analysis.

Blotting, Western↗
PubMed1993

Tenascin and decorin in epiretinal membranes of proliferative vitreoretinopathy and proliferative diabetic retinopathy.

Extracellular matrix (ECM) synthesis plays an important part in the pathogenesis of the intravitreal membranes and is thus characteristic of both proliferative vitreoretinopathy (PVR) and the involutive stages of proliferative diabetic retinopathy (PDR). Using a polyclonal antiserum against human decorin and a monoclonal antibody against human tenascin, we detected these molecules in membranes from patients with raumatic PVR (n = 10), idiopathic PVR (n = 8), and proliferative diabetic retinopathy (n = 8). We conclude that both tenascin and decorin play a role in the development of epiretinal PVR and PDR membranes by controlling cell adhesion and regulating ECM formation.

Antibodies, Monoclonal↗