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Biomedical subjects

R N Johnson

Publications and source records attributed to R N Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1988

Idiopathic macular holes. Observations, stages of formation, and implications for surgical intervention.

The authors have reviewed 158 eyes with evolving or completed idiopathic macular holes. Observations of these patients suggest that prefoveal vitreous cortex contraction is probably the cause of idiopathic macular holes. The earliest sign of an impending macular hole (stage 1) appears to be the development of a yellow spot or halo associated with loss of the normal anatomic foveal depression. No vitreous separation is present. This may resolve or progress to a small, early macular hole (stage 2). This hole gradually enlarged to a diameter of approximately 485 micron. The vitreous usually remained attached or a vitreofoveal separation developed (stage 3). Some eyes had complete posterior vitreous separation (stage 4). The implications for surgical intervention are discussed. A prospective study should be undertaken to confirm these findings and to investigate the feasibility of vitrectomy intervention to peel the prefoveal vitreous cortex in eyes with a stage 1 lesion.

Adult↗
PubMed1988

Tissue plasminogen activator treatment of postoperative intraocular fibrin.

Intraocular recombinant tissue-type plasminogen activator was used for treatment of postoperative intraocular fibrin clots. Using a rabbit vitrectomy and cyclocryotherapy model of postoperative fibrin, rabbits were randomized on the first postoperative day to receive either an anterior chamber injection of lactated Ringer's solution or 25,000, 50,000, or 100,000 IU tissue plasminogen activator (tPA). An intraocular dose of 25,000 IU of tPA produced marked resolution of the fibrin clot 24 hours later. A 50,000 and 100,000 IU dose produced slightly more resolution of the fibrin. No ophthalmoscopic or histologic evidence of intraocular toxicity was seen.

Animals↗
PubMed1988

A prospective, randomized, clinical trial of heparin therapy for postoperative intraocular fibrin.

The authors undertook a study to investigate the ability of systemic or heparin supplementation of the vitrectomy infusion solution to prevent formation of postoperative intraocular fibrin membranes. A total of 73 eyes were randomized; 26 served as the control group, 23 received 10,000 IU of intravenous bolus of heparin, and 12 eyes each underwent the vitrectomy with an infusion solution containing 10 or 5 IU/cc of heparin. Intraoperative bleeding, postoperative bleeding, and postoperative fibrin formation were graded. A 10-IU/cc heparin infusion resulted in a statistically significant reduction in postoperative fibrin formation (P = 0.04) but increased intraoperative bleeding (P = 0.02). A trend toward reduced postoperative fibrin formation was noted in the intravenous heparin and 5 IU/cc infusion groups.

Fibrin↗
PubMed1988

Effect of stimulation in three subcortical sites on the thalamocortical augmenting response in the cat.

The thalamocortical augmenting response is a complex multineuronal response which can be elicited by repetitive stimulation of the ventrolateral thalamus. A major function of the ventrolateral thalamus is known to be a result of its participation in central nervous system activity related to motor behaviour. The significance of the thalamocortical augmenting response itself is not known. Since it would be reasonable to relate that response to motor behaviour, we evaluated the effect on the thalamocortical augmenting response of the stimulation of two other central nervous system structures which are also thought to participate in motor control, the cerebellum and the red nucleus. We conclude that at least part of the effect of red nucleus stimulation on the thalamocortical augmenting response is exerted through a rubro-olivo-cerebellar pathway. We then compared the effects of red nucleus and of cerebellar stimulation to the effect of stimulating a non-motor mesencephalic site, the periaqueductal gray. The changes induced in the thalamocortical augmenting response appear not to be fully explicable solely in terms of changes in motor behaviour.

Animals↗
PubMed1988

Inaccuracy in measuring glycated albumin concentration by thiobarbituric acid colorimetry and by boronate chromatography.

We compared thiobarbituric acid colorimetry and boronate chromatography for measuring glycation of serum proteins. With 14C-glycated human albumin as a test material, both methods were acceptably linear and precise. However, comparable estimates (mmol/L) of albumin glycation ranged from 0.22 for thiobarbituric acid to 0.05 for boronate, representing yields relative to [14C]glycosylprotein of 42% and 10%, respectively. The low yield with thiobarbituric acid was corroborated independently on the basis of kinetic differences between the reactions of fructose standards and of glycosylprotein, leading to underestimation of glycosylprotein concentration. The lower estimate of glycosylprotein by boronate chromatography was related to an apparent requirement for two [14C]glyco groups per albumin molecule to effect binding.

Chromatography↗
PubMed1987

Relationship between albumin and fructosamine concentration in diabetic and non-diabetic sera.

We investigated the contribution of albumin to serum fructosamine activity. On gel exclusion chromatography, pooled diabetic and pooled non-diabetic sera before and after incubation with [14C]glucose differed in fructosamine activity and radioactivity mainly in the albumin-containing fractions. We confirmed the major contribution of glycated albumin to serum fructosamine concentration using affinity chromatography on Blue Sepharose. The importance of high molecular mass species was further demonstrated by the recovery of reducing activity following dialysis and charcoal treatment. Fructosamine measurements in diabetic patients were not correlated with serum albumin concentration in individuals with urinary albumin less than 1 g/l. We conclude that fructosamine activity is a convenient measure of glycosylprotein concentration and that the index responds mainly to glycation of albumin. However, routine correction for serum albumin concentration is inappropriate.

Adolescent↗
PubMed1987

Endolaser, cryopexy, and retinal reattachment in the air-filled eye. A clinicopathologic correlation.

We report the histopathology of intraocular argon blue-green laser photocoagulation lesions and transscleral cryopexy lesions in the air-filled human eye. Two days after treatment, the cryopexy lesions showed full-thickness retinal involvement, including disruption of the internal limiting lamina. The laser lesions showed full-thickness involvement as well. These observations emphasize the need for caution with thermal treatment modalities in the air-filled eye. Ophthalmoscopic examination 48 hours following vitrectomy, internal drainage of subretinal fluid, and gas fill of the vitreous cavity for diabetic macular detachment of several months' duration showed the retina to be attached. However, histopathologic examination revealed a thin layer of persistent subretinal fluid, demonstrating that it may take longer than is clinically apparent for true retinal reattachment to occur following gas tamponade of posterior retinal breaks. Prolonged gas tamponade may be necessary before retinal reattachment, with reestablishment of photoreceptor-pigment epithelial adherence, can be expected to help seal unrecognized or untreated posterior retinal breaks.

Choroid↗
PubMed1987

Histopathology of krypton red laser panretinal photocoagulation. A clinicopathologic correlation.

The histopathologic appearance of five-day-old and 14-day-old krypton red laser-created panretinal photocoagulation lesions in the diabetic human eye is described. The five-day-old lesions were examined near the equator. The 14-day-old lesions were near the temporal arcades and optic disc. Both groups of laser lesions showed a similar degree of damage and occlusion in the lamina choriocapillaris and deeper choroidal vessels. The 14-day-old posterior laser lesions showed outer retinal damage, whereas the five-day-old peripheral lesions showed full-thickness retinal involvement, probably because the peripheral retina is approximately half the thickness of the posterior retina. The five-day-old lesions showed no evidence of repair, whereas the 14-day-old lesions showed an adhesion formed with tight junctions binding Müller's fibers to retinal pigment epithelium.

Diabetic Retinopathy↗
PubMed1987

A Monte Carlo technique for signal level detection in implanted intracranial pressure monitoring.

Statistical monitoring techniques like CUSUM, Trigg's tracking signal and EMP filtering have a major advantage over more recent techniques, such as Kalman filtering, because of their inherent simplicity. In many biomedical applications, such as electronic implantable devices, these simpler techniques have greater utility because of the reduced requirements on power, logic complexity and sampling speed. The determination of signal means using some of the earlier techniques are reviewed in this paper, and a new Monte Carlo based method with greater capability to sparsely sample a waveform and obtain an accurate mean value is presented. This technique may find widespread use as a trend detection method when reduced power consumption is a requirement.

Biomedical Engineering↗
PubMed1987

Heparin prophylaxis for intraocular fibrin.

The authors have evaluated the use of heparin as a method to prevent postoperative intraocular fibrin clot formation in the rabbit after vitrectomy and cyclocryotherapy. In addition, they have studied the effect of a heparin infusion on intraocular bleeding after sectioning of retinal vessels. Heparin was administered by several different routes. The extent of the postoperative fibrin clot, as well as the number of days until its clearing, were recorded. A single anterior chamber injection, heparin supplementation of the infusion solution, or a single intravenous (IV) injection, all resulted in a statistically significant reduction of postoperative intraocular fibrin. Once daily subcutaneous injections alone did not produce a reduction in postoperative fibrin. No ocular bleeding complications developed postoperatively. A constant heparin intraocular infusion of 10 IU/cc did not change the bleeding time after sectioning of a retinal vessel.

Animals↗
PubMed1986

Inferences from beading of a retinal vein draining a choroidal melanoma.

Beading of a retinal vein draining a choroidal melanoma is reported, showing that the endothelial proliferation producing the beading is a response to some blood borne factor(s) traversing the vein and that retinal capillary non-perfusion adjacent to the beaded vein is not a necessary part of the process.

Capillaries↗
PubMed1986

Extended retinal tamponade in the treatment of retinal detachment with proliferative vitreoretinopathy.

We have used intraocular sulphur hexafluoride or liquid silicone as an adjunct to vitreous surgery in the treatment of a non-randomised sequential series of 19 eyes with retinal detachment complicated by proliferative vitreoretinopathy. We have studied the surgical results and complications of these two tamponades and drawn preliminary conclusions on their use in retinal reattachment surgery. After a seven-month minimum follow-up 13 (68%) of the eyes have reattached retinas. Six (60%) of 10 eyes treated only with silicone have reattached retinas, and four (67%) of six eyes treated only with sulphur hexafluoride gas tamponade have reattached retinas. An additional three eyes treated initially with silicone oil subsequently developed retinal detachments; all were successfully reattached with sulphur hexafluoride tamponade after silicone oil removal. Intraoperative pneumatic retinal reattachment to assess relief of retinal traction combined with the production of widespread chorioretinal adhesions to wall off persistent anterior traction and detachment, as well as extended postoperative gas tamponade of the retina, appears to enhance the surgical results in retinal detachment complicated by proliferative vitreoretinopathy. Silicone oil tamponade of the retina appears to be useful in cases where retinal traction cannot be entirely relieved and in patients who are unable to tolerate the head positioning required for effective gas tamponade of the retina. A controlled clinical study recently begun will be required to define further the precise role of these methods of retinal tamponade.

Adult↗
PubMed1986

The alkaline reducing activity of glycated serum proteins and its relevance to diabetes mellitus.

We investigated the ability of the fructosamine assay to detect glycation of serum proteins. We incubated both whole human serum and serum protein fractions in vitro with [14C]glucose, and analyzed for reducing activity and for uptake of 14C by protein. In all experiments, the reducing activity increased linearly with time for seven days and was correlated with 14C uptake (r = 0.94-0.98). Protein ketoamines were about fivefold more actively reducing than equimolar concentrations of deoxymorpholinofructose, the fructosamine standard, which explains why values for fructosamine in serum are higher than the expected concentration of protein ketoamines. We also used [14C, 2-3H]glucose to assess the contribution of the aldimine component to 14C uptake. Whole human serum and albumin incubated with [14C, 2-3H]glucose showed little uptake of 3H in relation to 14C. We conclude that glycated protein can be simply and reliably quantified by the fructosamine assay, and we discuss the relevance of this conclusion to the monitoring of diabetes.

Blood Proteins↗