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Biomedical subjects

H D Schubert

Publications and source records attributed to H D Schubert.

At least 19 recordsLinked to original sources
PubMed1998

Ocular manifestations of systemic hypertension.

Recent population-based studies suggest that the fundus lesions of hypertension also occur in people without hypertension. In experimental studies, hypertensive lesions, which used to be the backbone of older classifications of the severity of hypertension, did not correlate sufficiently with severity to allow reliable grading. Hypertensive retinopathy, choroidopathy, and optic neuropathy are independent processes. Vascular narrowing appears to occur early in the disease process, whereas retinal hemorrhages and retinal lipid may occur later. Branch vein occlusion is a complication of hypertension, whereas open-angle glaucoma may not be. Choroidal neovascularization in the fellow eyes of patients with macular degeneration is associated with high blood pressure. Laser treatment for this disorder is less effective in patients with high blood pressure than it is in normotensive individuals, which suggests that choroidal neovascularization may be an expression of chronic hypertensive choroidopathy. Hypertensive optic neuropathy, a variant of ischemic optic neuropathy, has delayed onset compared with retinopathy and, in experimental studies, has not been linked to the severity of hypertension. Given these findings, it may be better to describe than to grade fundus lesions. In either event, it is important to take blood pressures accurately. Fundus lesions suggest high blood pressure. Sphygmomanometry is more specific and reliable than funduscopy in making that diagnosis.

Blood Pressure↗
PubMed1997

Macular holes: migratory gaps and vitreous as obstacles to glial closure.

PURPOSE: Retinal glia may play an important role in the closure of macular holes. This in vitro study examines whether and how the specific pathoanatomy, including foveal eversion and foveal vitreous, may interfere with glial closure of macular holes. METHODS: Culture dishes used to grow glial cells were modified by the placement of slopes, vertical steps, and gaps to mimic the in vivo migratory surface in and surrounding macular holes. In separate experiments, defects were made in a rodent glial monolayer. These defects were exposed to hyaluronic acid (HA) and to rabbit (RV) and bovine (BV) vitreous gel. The migratory behavior and completeness of closure of defects were compared to controls. RESULTS: As expected, glial cells migrated further and in greater numbers on a smooth surface. Slopes and steps were moderate obstacles to migration; gaps in the surface were absolute obstacles. HA modified the pattern of adhesion of cells at the bottom of defects. Defects in the glial monolayer were repaired in 5-7 days. Compared to these controls, repair was inhibited by 11% (n.s.), 28% (P = 0.02), and 58% (P = 0.004) after direct exposure of defects to HA, RV and BV, respectively. CONCLUSION: The elevated and everted margins of macular holes represent slope, step, and gap-like obstacles to the migration of glial cells and hence to the healing of defects. The defect allows extension of extracellular matrix into it and the subretinal space. Our results indicate that gaps in the migratory surface caused and aggravated by eversion and the presence of vitreous present obstacles to glial migration and closure of macular holes.

Animals↗
PubMed1995

Schisis-like rhegmatogenous retinal detachment associated with choroidal colobomas.

BACKGROUND: The breaks that cause retinal detachments in colobomatous eyes are often hidden within the lesion and difficult to find. METHOD: To elucidate the pathoanatomy and possible pathomechanism of such detachments, histological sections of eight choroidal colobomas were reviewed. RESULTS: Sections of the margin showed central continuation of the inner neuroblastic layer (the intercalary membrane) and eversion and separation of the outer neuroblastic layer. The opposite direction of continuity of the neuroblastic layers created a schisis-like configuration between the intercalary membrane and the everted outer retina. The zone of duplication was a point of retinal adhesion, but also a locus minoris resistentiae due to vitreous attachments and variable glial support at the margin. CONCLUSION: The subset of coloboma-associated retinal detachments requires both a central break in the inner layer and a break in the outer layer at the margin of the coloboma. The inner layer break may be precipitated by retinovascular ischemia or scleral stretching; that in the outer layer may be caused by vitreous traction on the margin of the coloboma or extension of the formerly isolated detachment through the outer marginal zone of decreased glial support.

Child, Preschool↗
PubMed1995

Endoscopy and biopsy of the orbit.

Flexible endoscopes produce high-quality images, are small in size, and can deliver microsurgical instruments or laser probes. Early attempts at orbital endoscopy were limited by the relatively large size and poor visualization of rigid endoscopes. We performed endoscopic orbital exploration using the Olympus HYF flexible endoscope in four live dog orbits. We achieved excellent visualization of orbital structures including the globe, blood vessels, extraocular muscles, intermuscular septa, optic nerve, and fat. Visualization, hemostasis, and dissection were aided by the use of hyaluronic acid infused through the endoscope. We biopsied fat and extraocular muscle without complication using Olympus endoscopic cup biopsy forceps (confirmed by histopathologic examination). Our experience indicates that orbital endoscopy aided by viscoelastic hydrodissection may permit a less invasive approach to optic nerve sheath fenestration, tumor biopsy and treatment, and the removal of foreign bodies.

Adipose Tissue↗
PubMed1994

Cytologically proven seronegative Lyme choroiditis and vitritis.

PURPOSE: To report on a vitreous specimen in a 53-year-old patient with unilateral choroiditis and vitritis of unknown cause. METHODS: Cytologic examination of a vitreous aspirate stained by the Papanicolaou method. RESULTS: Intravitreal spirochetes consistent with Borrelia burgdorferi were found in this seronegative patient. CONCLUSION: Vitreous specimens of patients with choroiditis and vitritis of unknown cause should be examined cytologically, particularly when serologic results do not corroborate the clinical findings of Lyme disease.

Antibodies, Bacterial↗
PubMed1993

Postvitrectomy hypotonia: the role of the vitreous and retinochoroidal lesions.

The pathomechanisms of hypotonia after vitrectomy remain obscure. To examine the possible escape of intraocular fluid through the ocular wall, hydraulic fluid conductivity was measured across preparations of retina, pigmented epithelium, and choroid isolated from rabbit eyes 1, 3, 5, or 7 weeks after the production of laser or cryopexy lesions. The hydraulic conductivity measured in a modified Fischbarg-Bourguet chamber, was 0 in controls. At 1 and 3 weeks after transpupillary diode laser coagulation of the equatorial retina, hydraulic conductivity was measurable. However, the conductivity of these preparations returned to 0 by 5 weeks. After transscleral cryopexy, conductivity remained elevated for 7 weeks. Break-up of residual cortical vitreous with hyaluronidase increased the conductivity of "mature" cryopexy lesions to the values obtained 1 week after injury. These results suggest that there is escape of fluid across retinochoroidal lesions; fluid conductance typically decreases over time; an intact cortical gel can hinder conductance and seal the retinochoroidal leak. Thus, the risk factors for hypotonia appear to include extensive retinochoroidal lesions and the absence of a normal cortical vitreous in aphakia and/or after aggressive vitrectomy.

Animals↗
PubMed1990

Quantitative CW Nd:YAG pars plana transscleral photocoagulation in postmortem eyes.

The effect of different types of burns and numbers of lesions on, and the role of initial pressure head in, the rate of aqueous outflow was studied in enucleated human and porcine eyes. Noncontact and contact CW Nd:YAG laser applied to human eyes 3 mm posterior to the limbus produced a 34% and 51% increase, respectively, in outflow as compared with controls (P = .01). In porcine eyes, outflow increased directly with the number of noncontact burns as well as with the amount of perfusion pressure. Our results suggest that intraocular pressure and outflow are functions of both the intensity of irradiation and the surface area treated, and that each individual pressure head may require an optimal pars plana area of treatment of therapeutic degree to lower pressure and yet prevent overfiltration and phthisis. Our results also suggest that there may be a passive transneuroepithelial and transscleral outflow component in clinical laser cycloablation and, therefore, a need to grade laser treatments in order to prevent visual loss through unnecessary injury.

Animals↗
PubMed1990

Changes in aqueous outflow after in vitro neodymium: yttrium aluminum garnet laser cyclophotocoagulation.

To examine the possible role of transscleral outflow routes, enucleated human and porcine eyes underwent noncontact neodymium:yttrium aluminum garnet (Nd:YAG) laser cyclophotocoagulation 3 mm posterior to the limbus. Pars plana lesions were verified histologically. The eyes were perfused with saline solution at 50 mm Hg perfusion pressure, placing the tip of the needle into the hyaloid orbicular space. The outflow facility was 0.072 microliter/min/mm Hg in paired controls and 0.105 microliter/min/mm Hg in human lasered eyes, a difference of 31%. In porcine eyes the difference was 43%. Since concepts of aqueous production, impaired circulation, and inflammation do not apply to enucleated eyes, the increase may be related to pars plana transscleral flow facilitated by disruption of the neuroepithelial barrier.

Animals↗
PubMed1989

Contact transscleral retinopexy using a sapphire crystal probe.

To examine the laser-tissue interactions for contact transscleral irradiation, argon and CW Nd:YAG light was delivered through a synthetic sapphire crystal which was held in direct conjunctival contact perpendicular to the peripheral retina. The threshold for retinal whitening was 0.5 J in the rabbit, 1.0-1.5 J in the monkey, and 1.0-4.0 J in human eyes. Histologic examination of the acute injury and at 2 days, 1, 3, 6, and 12 weeks, showed coagulative lesions centered around the pigmented layers in the rabbit. While severe chorioretinal disruption and hemorrhage did occur depending on species, energy level, and probe location, no scleral perforation was noted at any setting. These preliminary studies suggest that transscleral contact lasers may be used safely in clinical situations where selective ablation of the peripheral retina or pigmented tissues is the primary objective.

Animals↗
PubMed1989

Noncontact and contact pars plana transscleral neodymium: YAG laser cyclophotocoagulation in postmortem eyes.

Transscleral neodymium:YAG (Nd:YAG) laser energy (5 J), noncontact at 20 msec and contact at 0.5 sec exposure time, was applied to enucleated porcine and human eyes 3 mm posterior to the limbus. Coagulative pars plana lesions were noted in all cases. Related to focus and exposure time, noncontact lesions were larger, more homogeneous, and affected primarily the pigment epithelium, whereas contact lesions showed more full-thickness thermal effects, including sclera. Because the corona ciliaris was unharmed when laser applications were made 3 mm from the limbus, this commonly used clinical focus raises questions about cyclo "destruction." Future clinical research will have to show which phenotype of pars plana lesion correlates best with long-term lowering of pressure.

Animals↗
PubMed1989

Intraocular pressure after peripheral retinal cryopexy in normotensive human eyes.

Intraocular pressure (IOP) was measured before and after peripheral retinal cryopexy given for lattice degeneration and small retinal breaks. During the period of observation the IOP of treated eyes decreased, suggesting that freezing of areas remote from the ciliary body may lower IOP through mediation and/or transscleral outflow.

Cryosurgery↗
PubMed1989

The role of inflammation in CW Nd:YAG contact transscleral photocoagulation and cryopexy.

Cyclodestructive modalities in humans have been shown to be effective when applied 3.5 mm or more posterior to the limbus. Therefore, CW Nd:YAG contact transscleral laser and cryopexy were applied 6 mm posterior to the limbus of pigmented rabbits. The intraocular pressure (IOP), flare, iritis, cells and conjunctival hyperemia were monitored clinically up to 3 weeks. The pressure lowering effect was -7.5 +/- 7.7 mm Hg for laser retinopexy and -14.2 +/- 6.0 mm Hg for retinocryopexy at 3 weeks and was comparable to application of the same modalities directly over the ciliary body. Similarly, induction of intraocular inflammation by injecting 10 micrograms of endotoxin intravitreally lowered IOP significantly. These findings suggest that hypotension may not be directly due to cyclodestruction but may be related to the ocular irritative response and extent of neuroepithelial defect, irrespective of its distance from the limbus.

Animals↗