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Biomedical subjects

R N Johnson

Publications and source records attributed to R N Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1992

Bread crumb-flecked retinopathy.

The case of a young girl with bilateral retinal flecks, normal fluorescein angiography results, and normal electrophysiologic findings is reported. The fundus appeared to consist of multiple, scattered, pale, bread crumb-like lesions that seemed to lie deep to the retinal vessels and anterior to the retinal pigment epithelium. The lesions were located outside the posterior pole in the midperiphery, and spared the macula and perimacular areas. The disorder may be associated with anomalies of the central nervous system and extraocular motility. No reports of similarly described fundus lesions have been found in the literature.

Child↗
PubMed1992

Identification of phlebotomine sandfly bloodmeals from Baringo District, Kenya, by direct enzyme-linked immunosorbent assay (ELISA).

Direct enzyme-linked immunosorbent assay (ELISA) was used to identify the sources of bloodmeals in phlebotomine sandflies from Baringo District, Rift Valley Province, Kenya. Some bloodmeals had been stored for over 4 years before being analysed. Among 356 sandflies identified, 62.9% were Phlebotomus martini, 14.8% Sergentomyia antennatus, 10% S.schwetzi, 6% S.clydei, 1.9% S.adleri, 1.6% P.duboscqi, 1.4% S.africanus and 0.8% S.bedfordi. Out of 224 P.martini bloodmeals, host source was identified for 69. The order of host preference for P.martini was: goat 28.5%, rabbit 22.7%, human 8.9% and others 8.9%. Evidence of mixed feeding was shown by four species comprising sixteen specimens, twelve of which were P.martini. The most effective methods for trapping bloodfed P. martini were sticky paper traps in termite hills, followed by light-traps. Of the 224 P.martini trapped, 58.9% were collected with traps in termite hills, and 22.7% with light traps. Roles of the three most popular hosts for P.martini should be investigated to ascertain whether they act as reservoirs in the transmission of Leishmania donovani causing visceral leishmaniasis in Kenya.

Animals↗
PubMed1992

Possible determination of the vector and reservoir of leishmaniasis in the Dominican Republic.

Two species of sand flies were collected by various methods from sites in the Dominican Republic. Lutzomyia cayennensis hispaniolae was the more common of the two. It was found in wooded habitats from sea level to an elevation of 442 m. This species was observed feeding on lizards (Anolis sp.) in the wild. In the laboratory, it fed only on lizards and only under lighted conditions. The other species, Lu. christophei was only found in the vicinity of seven leishmaniasis case sites. It readily fed on or probed rodents and humans. Although no naturally infected sand flies were collected, in the laboratory Lu. christophei was readily capable of transmitting the Dominican Leishmania parasite to uninfected BALB/c mice. We collected 167 specimens of three species of rodents and three Herpestes auropunctatus (mongoose) from the vicinity of two case sites. All four species are non-endemics introduced in post-Columbian times. Although we were unable to isolate parasites from any of these specimens, four of 44 Rattus rattus from one case site were seropositive for antibodies against Leishmania by indirect fluorescent antibody testing. This represents the first report of transmission of the Dominican Leishmania parasite by a sympatric species of sand fly and suggests that commensal rodents may play a role in the epidemiologic cycle.

Animals↗
PubMed1991

Significance of variation in turnover of glycated albumin on indices of diabetic control.

We measured the half-time of disappearance of 125I-labelled glycated albumins in a rat model of diabetes with continuous infusion of physiological saline and insulin. Our results indicate that (i) in non-diabetic rats, continuous infusion of saline per se did not affect the concentrations of glucose or of fructosamine, and the half-time of disappearance of albumin was unaffected by degree of glycation; (ii) hyperglycaemia (mean plasma glucose concentration of 18-27 mmol/l) caused a small but significant increase in half-time of labelled glycated albumin disappearance from a mean of 42 h to a mean of 47 h; (iii) this effect of hyperglycaemia outweighed any effect of increase in albumin excretion detected in poorly controlled diabetic rats without infusion. We conclude that the effect of hyperglycaemia in slowing turnover of glycated albumin is likely to be insignificant in relation to its effect in promoting glycation, and may be species-dependent. However, in nondiabetics, variation of turnover of glycated albumin may well be significant in explaining the wide interindividual variation in concentration of glycated protein.

Albuminuria↗
PubMed1991

Progressive enlargement of laser scars following grid laser photocoagulation for diffuse diabetic macular edema.

Laser photocoagulation in a grid pattern is effective in many eyes in resolving diffuse diabetic macular edema and stabilizing vision. We retrospectively studied 203 eyes of 203 patients, all of whom had diabetic macular edema treated with grid laser photocoagulation. During the follow-up period, 11 of these 203 eyes developed enlargement of the laser scars that progressed into the central fovea. Each of the 11 eyes experienced loss of vision, and in five, the visual loss was significant. Five of these eyes also developed a retinal pigment hyperplastic scar. After the laser treatment, but before the scars enlarged, the visual acuity of these eyes was unchanged from that before treatment. But after the atrophic scars enlarged into the central fovea, visual acuity in one eye decreased from 20/40 to 20/100, and the other 10 eyes had visual acuities of 20/200 or worse.

Aged↗
PubMed1991

Clinicopathologic correlation of retinal to choroidal venous collaterals of the optic nerve head.

An optic nerve meningioma developed in an elderly woman and was followed for 13 years until her death. The optic nerve was initially normal. Over time it became swollen and then atrophic and developed retinal venous to choroidal venous collaterals. Five hundred serial sections were prepared through the optic nerve and for approximately 1.5 mm superiorly and inferiorly to the optic nerve to trace the course of the collaterals that were seen ophthalmoscopically and angiographically in the optic nerve head. This clinicopathologic study shows clearly that the abnormal channels are, in fact, retinal venous to choroidal venous collaterals (bypass channels). Four collaterals extended around the end of Bruch's membrane at the optic nerve head. Two more collaterals extended through the retinal pigment epithelium to become continuous with a subretinal pigment epithelial neovascular membrane, the vessels of which connected with the choroidal vessels through a defect in Bruch's membrane.

Aged↗
PubMed1991

Cilioretinal artery occlusion in young adults with central retinal vein occlusion.

Ten patients, all younger than 50 years of age, had a temporal cilioretinal artery occlusion associated with a nonischemic central retinal vein occlusion. On fluorescein angiography, the cilioretinal artery eventually filled in all but one eye. The cilioretinal artery showed pulsations on fluorescein angiography in five eyes. The central retinal vein occlusion eventually resolved and the fundus assumed a normal appearance in all nine of the followed cases. Eight of nine eyes that underwent follow-up examination had final visual acuity of 20/30 or better. The occlusion of the central retinal vein produces an elevation of intraluminal capillary pressure because the central retinal artery continues to pump blood into the retina. Because the perfusion pressure of the cilioretinal artery is lower than the central retinal artery, it becomes relatively occluded. The prognosis for these patients is generally good unless the entire parafoveal capillary net is affected by the cilioretinal artery that is occluded.

Adult↗
PubMed1991

Recent advances in laboratory mass rearing of phlebotomine sand flies.

Recent technical and procedural advances in mass rearing of sand flies have resulted in larger, healthier, and less labor-intensive colonies. We now maintain closed colonies of Phlebotomus papatasi, P. duboscqi, P. argentipes, and Lutzomyia longipalpis which produce up to 1,000 females per week, in excess of colony-maintenance requirements, for use in research. Advances include larval food preparation in acrylic-plastic incubator cabinets, strict regulation of food quantity and moisture in 500-ml plaster-lined rearing jars, use of large plaster-lined adult holding/mating cages and vacuum-powered aspirators for trauma-free handling of adults.

Animal Feed↗
PubMed1991

A study of five calcium supplements: estimation of calcium absorption and sodium content.

Calcium absorption from five proprietary calcium supplements (Calcium-Sandoz, Cal-Sup, Effercal, Oscal and Oscal Chewable) was examined in 12 healthy female volunteers. Supplements providing 1 g of elemental calcium were studied in random order at weekly intervals. Using increments in urinary calcium excretion as an index of absorption, Calcium-Sandoz was absorbed best and Oscal the least. However, interindividual variation of calcium absorption appeared at least as significant as variation between the supplements themselves. Sodium content of the supplements was insignificant for all except Calcium-Sandoz which included 0.4 g of sodium/g of calcium (equivalent to 1 g of NaCl). This amount represents a substantial proportion of the recommended daily intake for those on a sodium-limited diet.

Adult↗
PubMed1990

Retinal toxicity of recombinant tissue plasminogen activator in the rabbit.

We studied the dose-dependent retinal toxicity of the available commercial preparation of human recombinant tissue plasminogen activator in the normal rabbit eye. Tissue plasminogen activator was injected into the midvitreous cavity of albino rabbits in doses (per 100 microL) of 25, 50, 75, and 100 micrograms. Control eyes received 100 microL of balanced salt solution or tissue plasminogen activator vehicle. No evidence of a retinal toxic reaction was seen in eyes receiving 25 micrograms of tissue plasminogen activator. One of four eyes injected with 50 micrograms showed loss of photoreceptor cells by light microscopy. Severe retinal damage was seen by ophthalmoscopy, electroretinography, and light microscopy in three of four eyes receiving 75 micrograms of tissue plasminogen activator and in all eyes treated with 100 micrograms of tissue plasminogen activator or equivalent vehicle. These results suggest that the commercial recombinant tissue plasminogen activator formulation has a narrow margin of safety in nonvitrectomized eyes and that a component of the vehicle is the toxic factor.

Animals↗
PubMed1990

Retinal pigment epithelial folds associated with retinal pigment epithelial detachment in macular degeneration.

The authors reviewed six eyes that had a shallow retinal pigment epithelial detachment with the retinal pigment epithelium (RPE) thrown into folds. A contraction of subpigment epithelial fibrovascular tissue causes a folding of the overlying, intimately adherent RPE. Retinal pigment epithelial folds are a sign of subretinal neovascularization and are another manifestation of age-related macular degeneration.

Aged↗
PubMed1989

Transient hypopyon with marked anterior chamber fibrin following pars plana vitrectomy and silicone oil injection.

In a retrospective review of 30 cases of complex retinal detachment, which had been managed by pars plana vitrectomy techniques together with silicone oil injection, we found that two patients developed marked postoperative anterior chamber fibrin and hypopyon. In all 30 cases, the same silicone oil was used: purified and heat-sterilized trimethylsiloxy-terminated, polydimethylsiloxane of 1000-centistoke viscosity. Although the silicone oil itself remained clear and without emulsification, the differential diagnosis of this postoperative inflammation included microbial endophthalmitis. These two cases were treated with frequent topical steroids and antibiotics while we closely monitored the retraction of the anterior chamber fibrin. In both cases, clinical improvement and long-term retinal reattachment with satisfactory visual function were achieved. The use of intense scatter laser endophotocoagulation and the presence of impurities in the silicone oil may have contributed to the excessive postoperative inflammation in these cases.

Anterior Chamber↗
PubMed1989

Intravitreal tissue plasminogen activator treatment of experimental vitreous hemorrhage.

Intraocular recombinant DNA human tissue-type plasminogen activator (tPA) can promote rapid resolution of intracular fibrin clots and hyphema. The efficacy of intravitreal tPA in promoting the short-term clearance of vitreous hemorrhage was investigated. Five treatment groups with experimentally induced vitreous hemorrhage were studied. The extent of the vitreous hemorrhage was graded based on the visibility of retinal details in each quadrant. Two weeks following intravitreal tPA injection (50,000 IU), the nonvitrectomized group and gas vitrectomy groups, each of which received a single tPA injection, showed a statistically significant reduction of the vitreous hemorrhage, although this was thought to represent only a modest clinical effect. Tractional retinal detachments were noted to develop more frequently in tPA-treated eyes as compared with controls.

Animals↗
PubMed1989

Additional Plasmodium species from Anolis lizards of Hispaniola and Panama.

Saurian malaria parasites in the Caribbean were previously represented by only two species, Plasmodium azurophilum and P. floridense. An additional three species of Plasmodium occur on Hispaniola which appear, because of morphometric and qualitative similarities, to be related to South and Middle American species: a subspecies of Plasmodium tropiduri in Anolis cybotes; a population of Plasmodium minasense anolisi in A. cybotes and A. distichus; and another parasite in A. distichus which is designated as a subspecies of a previously undescribed Plasmodium species in Anolis limifrons. Taxonomic descriptions based upon morphology of mature schizonts and gametocytes are given, the previously unknown parasites are described as new species/subspecies, and comparison is made with P. floridense which also occurs in their respective host species. A Fallisia species was also present but is not described. The increased diversity of Plasmodium parasites in Hispaniolan anoles is attributed to colonization of the island by four separate evolutionary lines of Anolis lizards, in comparison to fewer invasions of Jamaica and Puerto Rico, where only P. floridense and P. azurophilum are found.

Animals↗