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Biomedical subjects

R N Johnson

Publications and source records attributed to R N Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1995

Subretinal fibrosis in central serous chorioretinopathy.

PURPOSE: To report unusual and heretofore unreported visually damaging manifestations of severe central serous chorioretinopathy. METHODS: Case studies. RESULTS: Each of six male patients (average age, 40 years) had a form of severe central serous chorioretinopathy with at least one eye containing fibrin in the subretinal space that then developed into a subretinal fibrotic scar. Scar formation was followed by a tenting up of the macula, vascularization of the fibrosis (subretinal neovascularization), or a retinal pigment epithelial rip. Four of the seven eyes with subretinal fibrosis had severe visual loss (20/400 or worse). CONCLUSION: Subretinal fibrin and other extracellular matrix molecules appear to stimulate the retinal pigment epithelium to undergo fibrous metaplasia, which results in subretinal fibrotic scar formation and other sequelae, all of which can lead to severe visual loss.

Adult↗
PubMed1994

Two cases of intraocular infection with Alaria mesocercaria (Trematoda)

We encountered two cases of human intraocular infection with mesocercariae of Alaria (Trematoda), involving unrelated Asian men who had unilateral decreased vision. Both patients had pigmentary tracks in the retina, areas of active or healed retinitis, or both, and other signs of diffuse unilateral subacute neuroretinitis. Similar, nonnematode worms were seen in the patients' retinas and vitreous, respectively, several years after apparent infection. The worm in Case 1 was analyzed from projected fundus photographs and diagnosed as an Alaria mesocercaria on the basis of its shape, size (500 x 150 microns), and movement; it was successfully killed with laser. The worm in Case 2 was removed surgically from the vitreous and identified as A. mesocercaria, 555 x 190 microns, most likely A. americana. The probable source of infection in the patients was ingestion, in local restaurants, of undercooked frogs' legs containing A. mesocercaria. In addition to causing prolonged intraocular infection, A. mesocercaria was found to be a cause of diffuse unilateral subacute neuroretinitis, a condition previously attributed only to intraocular nematode larvae.

Adult↗
PubMed1994

Severe diabetic retinopathy after cataract surgery.

We retrospectively compared the visual acuity and degree of background diabetic retinopathy in 32 consecutive patients with diabetes who had cataract surgery in one eye (study group) and compared them with the visual acuity and degree of diabetic retinopathy in 32 patients with diabetes who had not had cataract surgery (control group) to determine if the retinopathy was asymmetric and worse in the operated-on eye. Twenty-three (72%) of the 32 study patients had asymmetric retinopathy (with the more severe retinopathy in the eye that underwent cataract surgery in each case) compared with three (9%) of the control group (P < .0005). The eyes that had cataract surgery did poorly in terms of visual acuity with no eyes achieving 20/20 or 20/25, only three eyes achieving 20/30 or 20/40, and 16 achieving 20/100 or worse.

Aged↗
PubMed1994

Surgical results in the vitreomacular traction syndrome.

PURPOSE: The vitreomacular traction syndrome is a distinct clinical entity in which partial posterior vitreous detachment is present in combination with persistent macular adherence, causing traction-induced visual deficit. The authors evaluate the results of vitreous surgery for this syndrome. METHODS: The authors reviewed 20 consecutive eyes that underwent vitrectomy and posterior hyaloid/epiretinal membrane stripping to better define the clinical features, visual results, and complications of surgery for the vitreomacular traction syndrome. FINDINGS: Eyes were categorized anatomically as having either "classic" vitreomacular traction syndrome (8 [40%] eyes had 360 degrees midperipheral vitreous detachment) or "variable" vitreomacular traction syndrome (12 [60%] eyes had a variety of midperipheral areas of vitreous separation). Release of vitreomacular traction resulted in improvement in vision of two or more lines in 15 (75%) eyes, with 8 (40%) obtaining 20/50 visual acuity or better. All eyes were followed for at least 6 months. Complications of vitreous surgery included progression of nuclear sclerosis (83% of phakic eyes), epiretinal membrane formation (40%), and retinal breaks (20%). CONCLUSION: The vitreomacular traction syndrome represents a wide spectrum of vitreoretinal anatomic configurations that can produce visual deficit. Vitrectomy surgery to release macular traction may improve visual acuity.

Aged↗
PubMed1994

Phlebotomine sandflies of Kenya (Diptera: Psychodidae). III. The identification and distribution of species of the subgenus Larroussius.

The six species of phlebotomine sandflies of the subgenus Larroussius recorded in Kenya are Phlebotomus aculeatus, P. elgonensis, P. guggisbergi, P. longipes, P. orientalis and P. pedifer. Five are proven vectors of leishmaniasis in that country or elsewhere. Males of all six can be identified by the morphology of the aedeagus or the number and position of the hairs on the inner surface of the coxite. Additional features separating some of the species are the sizes of the palpal and antennal segments. The females have usually been considered difficult or impossible to distinguish. A comparison of the base of the spermathecal ducts is made and it is shown that all six can be identified by this character alone. A map of Kenya is given, showing the presently known distribution of the six Larroussius species. Further surveys are necessary in parts of the country that have not been systematically surveyed.

Animals↗
PubMed1994

Phlebotomine sandflies associated with households of human visceral leishmaniasis cases in Baringo District, Kenya.

A 12-month field study on sandflies was conducted from April 1992 to March 1993 at three locations in Baringo District, Rift Valley Province, Kenya. Study sites were selected based on their close proximity to the households of three patients who had had parasitologically confirmed visceral leishmaniasis in 1988, 1990 or 1991. Sandfly populations were highest during the two rainy seasons, April-June and November-December. A significant association was detected between the monthly abundance of sandflies and rainfall in the previous month. A significantly higher proportion of females than males was collected in light traps than on sticky paper traps set in termite mounds or animal burrows: approximately twice as many males as females were collected from the sticky paper traps whereas twice as many females as males were collected in light traps. Over 10% of the female sandflies collected from animal burrows and termite mounds were gravid, indicating that these flies were seeking oviposition sites at these locations. A total of 2231 sandflies was collected and five females were found to have flagellates in their midguts. The flagellates cultured from four Sergentomyia spp. were tentatively identified as Crithidia sp. by cellulose acetate electrophoresis (CAE). The promastigotes from the one Phlebotomus martini female found with an infected midgut were identified as Leishmania donovani by CAE.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Central retinal vein occlusion associated with retinal arteriovenous malformation.

PURPOSE/BACKGROUND: Retinal arteriovenous malformations can be seen in a variety of ways and have multiple, associated, ocular changes that can affect vision. The authors report two cases of retinal arteriovenous malformation. In each case, a central retinal vein occlusion developed. METHODS: Each patient underwent clinical examination and fluorescein angiography. One patient was followed over a long period of time. CONCLUSION: The authors propose that a turbulent flow, high intravascular volume, and arteriolar pressure in the venous side of the retinal arteriovenous malformation may lead to vessel wall damage, thrombosis, and occlusion. They also suggest that compression of the central retinal vein by the mass effect of the arteriovenous malformation on the optic nerve further leads to turbulence and thrombosis.

Arteriovenous Malformations↗
PubMed1993

Phlebotomine sandflies of Kenya (Diptera: Psychodidae). I. The validity of Phlebotomus (Larroussius) elgonensis Ngoka, Madel and Mutinga.

Sandflies collected in Kitum cave on the Kenyan side of Mount Elgon were identified as Phlebotomus (Larroussius) elgonensis Ngoka, Madel and Mutinga, a species synonymized with P. (L.) aculeatus Lewis, Minter and Ashford, by D. J. Lewis. A comparison of the flies from Kitum cave with P. aculeatus from Lake Elmentaita, Kenya, shows marked differences in the lengths of: (a) the spermathecal ducts of the female; (b) the style, coxite, genital pump and aedeagus of the male; and (c) the palpal segments of both sexes. Other notable differences are in the shape of the base of the spermathecal ducts; the position of spines on, and the shape of, the tip of the aedeagus; and the appearance of the pharyngeal armatures of both sexes. Phlebotomus elgonensis is redescribed and it is concluded that it is sufficiently different from P. aculeatus to deserve recognition as a valid species.

Animals↗
PubMed1993

Trypanosome transmission by Corethrella wirthi (Diptera: Chaoboridae) to the green treefrog, Hyla cinerea (Anura: Hylidae).

Seventy-two percent of 215 male green tree frog, Hyla cinerea (Schneider), captured in Alachua and Levy counties, FL, between April and mid-September 1978 and 1979 were infected with an undescribed Trypanosoma sp. None of the 31 female frogs captured concurrently was infected. Periodic sampling of the peripheral blood from the infected male frogs showed that the trypanosomes were present in high numbers only at night. Conspecific trypanosomes also were found in the mid and hind guts of female Corethrella wirthi Stone flies collected on or near male frogs in the field. Transmission of the parasite to uninfected frogs was demonstrated by exposure of male and female frogs to naturally infected flies and to parasites injected subdermally. This is the first report of parasite transmission by a species of Corethrella.

Animals↗
PubMed1993

Use of creatine kinase isoforms for diagnosis of infarct artery patency after thrombolytic therapy with streptokinase.

BACKGROUND: We investigated whether the proportion of creatine kinase (CK) MM3 to total MM isoform, measured in a single blood specimen taken at 3 hours after starting intravenous administration of streptokinase to patients with developing myocardial infarction, would give reliable information on patency or occlusion of the infarct-related coronary artery. METHODS: Fifty-nine patients received streptokinase 1.5 x 10(6) U intravenously within 6 hours of onset of prolonged chest pain and ST-segment elevation. Patency of the infarct-related coronary artery was assessed by arteriography at 2.6 +/- 0.3 (SD) hours after starting streptokinase. Creatine kinase MM isoforms were measured by chromatofocusing in blood taken at 3 hours after streptokinase. RESULTS: A proportion of CKMM3 to total CKMM of greater than 50% was present in 34 of 34 patients (100%) with a patent, infarct-related artery at arteriography and whose peak total CK activity reached twice the upper normal limit for our laboratory (600 U/L). CKMM3/total CKMM was less than 50% in 14 of 18 patients (78%) in whom the infarct-related artery was occluded. In five of six patients with a nondiagnostic total CK rise (peak < 600 U/L), 3-hour CKMM3/total CKMM was less than 50% despite a patent artery. CKMM3 was not measurable in one patient. CONCLUSIONS: A proportion of CKMM3/total CKMM of greater than 50% is highly sensitive for prediction of infarct artery patency at 3 hours after administration of streptokinase. However, the test used in this way is not reliable for patients with "prevented" myocardial infarction. Also, positive tests do occur in patients with angiographically occluded arteries, possibly signifying intermittent reperfusion and occlusion.

Adult↗
PubMed1993

Host feeding preference of Phlebotomus guggisbergi, a vector of Leishmania tropica in Kenya.

Recently the sandfly Phlebotomus guggisbergi was found to be a vector of Leishmania tropica causing cutaneous leishmaniasis in the Laikipia focus, Kenya, but extensive searches have shed no light on the identity of the rural reservoir host(s). In order to discover more about the biology of the vector, a host feeding preference study was conducted on wild sandflies in their natural cave environment over a 6-month period. Solid state Army miniature (SSAM) traps, without light bulb, were suspended over cages with potential hosts or an empty cage control. The animals tested included sheep, goat, dog, cat, hamster, rabbit, giant rat (Cricetomys gambianus), crested rat (Lophiomys imhausi) and rock hyrax (Procavia capensis), all of which (except hamsters) are normally found in the vicinity of the study site. Sandfly collections from traps baited with goat, sheep, cat, dog, rabbit, or wild rodent species were significantly higher than the control, whereas trap collections with hamster and rock hyrax were not significantly different from the control. Numbers of sandflies collected from the goat, sheep and cat were significantly greater than from the rabbit and rodents. The sex ratio also varied between collections: larger animals attracted a higher proportion of female P. guggisbergi than did the smaller animals (P > 0.05). Therefore greater emphasis should be placed on surveying larger animals to assess their status as reservoir hosts for L. tropica in Kenya.

Animals↗
PubMed1993

Non-invasive diagnosis of arterial patency after thrombolytic treatment and its relation to prognosis.

OBJECTIVE: To validate a simple noninvasive method with serial creatine kinase measurements for diagnosis of early patency of the infarct related artery after thrombolytic treatment with streptokinase. To investigate the relation between early patency of the infarct related artery and prognosis. DESIGN: Patients under 76 years of age and seen within six hours of the start of prolonged chest pain and ST segment elevation were treated with streptokinase (1.5 x 10(6) U) intravenously over 30-60 minutes. Blood for measurement of total creatine kinase activity was taken at baseline and at 1, 2, 3, 4, 8, 12, 16, 20, and 24 hours after starting treatment. The rise in enzyme activity at each time from baseline was expressed as a proportion of the total rise from baseline to peak. PATIENTS: Patients studied were in the following groups: (a) Sixty patients took part in a validation study with angiographic determination of patency of the infarct related coronary artery at 2.6 (0.3) hours (mean (SD)) after starting streptokinase. (b) A further 258 patients did not have early arteriography, but data were added to those from the 60 validation patients to find the relation between enzymatically determined early patency of the infarct related artery and 30 day mortality. (c) A further subset of 232 patients with first infarctions (including patients from groups (a) and (b) had angiocardiography at three weeks after infarction, and data were used to investigate the relation between early patency of the infarct related artery and left ventricular function. MAIN OUTCOME MEASURES: Normalised rate of rise of creatine kinase activity at three hours after starting streptokinase in relation to angiographic patency of the infarct related coronary artery at 2.5 hours; 30 day cardiac mortality; and left ventricular function at three weeks in survivors of first infarction. RESULTS: In the validation study, a rise in three hour creatine kinase activity of > 20% of peak occurred in 34/37 patients with initially patent infarct related coronary arteries (sensitivity 92%), and a rise to < 20% of peak occurred in 21/23 patients with initially occluded arteries (specificity 91%). In the prognostic study, 30 day mortality was 2.1% in the 191 patients with three hour creatine kinase > 20% of peak and 8.7% in the 127 patients with three hour creatine kinase < 20% of peak (p < 0.01). Angiocardiography in three week survivors of anterior infarction (n = 95) showed better left ventricular function when three hour creatine kinase was > or = 20% than when it was < 20% of peak (mean (SEM) end systolic volume 71 (5) v 96 (9) ml, p < 0.02; ejection fraction 56% (2%) v 51% (2%), NS). CONCLUSION: Non-invasive determination of early patency of the infarct related artery by the normalised rate of rise of creatine kinase activity at three hours seems to be reliable, and may be prognostically important and of value for use in clinical trials.

Adult↗
PubMed1992

Central serous chorioretinopathy occurring in patients 60 years of age and older.

The authors report on 13 eyes in 13 patients, 60 years of age or older, with idiopathic central serous chorioretinopathy, a condition that typically presents in adults between the ages of 30 and 50 years. In older patients, this condition can easily be mistaken for macular degeneration with subretinal neovascularization. None of the patients in this series had soft drusen, geographic atrophy, or subretinal neovascularization, signs of age-related macular degeneration or other retinal or macular disease. Subretinal neovascularization was not seen either at the time of initial diagnosis or during follow-up. The clinical, biomicroscopic, and fluorescein angiographic characteristics of this entity are described. The clinical course of 7 of these 13 eyes that underwent laser photocoagulation treatment is also described.

Aged↗
PubMed1992

Central retinal vein occlusion in young adults (papillophlebitis).

We performed a retrospective study of 103 cases of central retinal vein occlusion (CRVO) in young, nondiabetic adults that were followed for at least six months. Of these patients, 64% were men and 36% were women. While visual acuity was usually good, 33 eyes (32%) had a final visual acuity of 20/200 or worse, including 6 eyes (6%) with a final visual acuity of no light perception. Ocular complications included chronic cystoid macular edema, macular pigmentary changes (37%), sheathing of retinal vessels (22%), venous collaterals of the disc (33%), macular hole formation (1%), neovascularization of the disc (1%), retina (1%), and iris (19%), neovascular glaucoma (8%), and vitreous hemorrhage (7%).

Adolescent↗