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Biomedical subjects

B C Leonard

Publications and source records attributed to B C Leonard.

At least 19 recordsLinked to original sources
PubMed2001

Vigabatrin effect on inner retinal function.

OBJECTIVE: To determine the degree of electroretinal dysfunction in a group of patients taking Vigabatrin (VGB). Additionally, to investigate the role of cumulative dosage, the role of VGB alone or in combination with other anticonvulsants, and whether recent discontinuance of VGB affects electroretinal function as measured by the electroretinogram (ERG). DESIGN: Retrospective, comparative case series. PARTICIPANTS: Forty patients (18 male, 22 female) with a mean age of 35 years were studied as three groups: the VGB multitherapy group (n = 24) included those taking VGB with other anticonvulsants, the VGB monotherapy group (n = 9) included those taking VGB alone, and the off-VGB group (n = 7) included those who had discontinued VGB in the last 6 months. METHODS: Scotopic flash, photopic flash, and 30-Hz flicker ERG results were recorded according to the International Society for Clinical Electrophysiology of Vision (ISCEV) standard. The clinical electro-oculogram (EOG) results were recorded according to the ISCEV standard. MAIN OUTCOME MEASURES: Implicit time and amplitudes of the A- and B-waves of the flash and 30-Hz flicker ERGs were recorded. Summed amplitude of the first three oscillatory potential wavelets were recorded. The light-peak to-dark-trough Arden ratio of the EOG was evaluated. RESULTS: Although photopic ERG B-wave reduction was most frequent in patients in the VGB multitherapy group (48% of eyes), a significant number of eyes in all three groups had scotopic ERG B-wave reduction. The 30-Hz flicker ERG result was abnormally reduced in all three groups. There was no significant difference in the frequency of occurrence in ERG result abnormalities between the VGB monotherapy and VGB multitherapy groups. The EOG results revealed reduced Arden ratios in all three groups; however, there was a significantly lower frequency of EOG abnormalities noted in the off-VGB group (P = 0. 0373). There was no statistically significant relationship between the frequency of electrodiagnostic abnormalities and the duration of use or the total cumulative dosage of Vigabatrin in any of the three groups. CONCLUSIONS: These findings of scotopic ERG result abnormalities suggest that VGB alone has an effect on inner electroretinal function at the level of the Müller cell. Concomitant EOG abnormalities suggest a substantial effect of VGB on outer retinal function that may be reversible after cessation of VGB treatment.

4-Aminobutyrate Transaminase↗
PubMed2001

Prevalence of factor V Leiden and activated protein C resistance in central retinal vein occlusion.

PURPOSE: Factor V Leiden is a common inherited mutation that is a significant risk factor for deep vein thrombosis. It results in resistance to activated protein C (APC). The association between factor V Leiden and central retinal vein occlusion (CRVO) remains controversial. This study was designed to determine the prevalence of APC resistance and the factor V Leiden mutation in patients with CRVO in a controlled study. METHODS: The study was designed as a case control study conducted in a tertiary care retina practice. The prevalence of APC resistance and factor V Leiden was determined by genetic testing of blood samples obtained from patients with CRVO and clinic control patients. RESULTS: Factor V Leiden was identified in 2.3% of patients with CRVO and 3.5% of clinic control patients. There was no significant association between the presence of factor V Leiden and CRVO (odds ratio, 1.13; 95% confidence interval, 0.65-1.98; P = 0.66). CONCLUSION: Factor V Leiden does not appear to be associated with CRVO. Routine screening of patients with CRVO does not appear to be warranted.

Activated Protein C Resistance↗
PubMed1999

Management of submacular hemorrhage with intravitreal sulfur hexafluoride: a pilot study.

BACKGROUND: Some success has been reported with the intravitreal use of tissue plasminogen activator (tPA) and perfluoropropane gas in the management of large submacular hemorrhages. However, the dosage of tPA that has been used (100 micrograms) has a narrow margin of safety, and it remains to be shown that intravitreal tPA can cross the retina and effect subretinal clot lysis. We carried out a pilot study to evaluate the efficacy of intravitreally administered sulfur hexafluoride (SF6) gas alone in the management of large submacular hemorrhages secondary to age-related macular degeneration (AMD). METHODS: Three patients with large submacular hemorrhages secondary to AMD seen at a university-affiliated teaching hospital in Ottawa were treated with an intravitreal injection of 0.6 mL of SF6 gas. They were instructed to assume a prone position for 7 to 10 days. The patients were followed 3, 7, 14 and 28 days after the procedure and monthly thereafter for at least 6 months. Colour photography and fluorescein and indocyanine green angiography were performed immediately before and 2 weeks after the procedure and, thereafter, at the discretion of the treating ophthalmologist. RESULTS: In all three cases significant inferior displacement of the submacular blood was observed. Two patients showed an improvement of vision from counting fingers to 20/70 and to 20/200. In one case the submacular blood was displaced such that laser photocoagulation of a juxtafoveal choroidal neovascular membrane became possible. INTERPRETATION: The results suggest that intravitreally administered SF6 alone may have a role in the management of selected cases of neovascular AMD complicated by significant submacular hemorrhage. These results call into question the utility of adjunctive intravitreal tPA in such cases.

Fluorescein Angiography↗
PubMed1995

Toxicity of intravitreal interferon alpha-2b in the rabbit.

OBJECTIVE: To investigate the toxicity of single doses of intravitreally administered interferon alpha-2b in the New Zealand white albino rabbit. INTERVENTIONS: One eye each of six rabbits received an intravitreal injection of 1000, 10,000, 100,000, 500,000, 1 million or 2 million units of interferon alpha-2b reconstituted in 0.1 mL of balanced salt solution. The fellow eye of the first three rabbits received an intravitreal injection of the same volume of balanced salt solution. OUTCOME MEASURES: Media opacities, toxic effects to the retina, optic nerve or other ocular structures. RESULTS: The injection of 2 million units of interferon alpha-2b elicited an immediate dense vitreous haze that largely cleared within 24 hours as well as numerous intraretinal hemorrhages that were no longer visible 7 days after injection. Histopathological study of this eye 14 days after injection showed a diffuse mixed inflammatory cell infiltrate with retinal vacuolation and ganglion cell dropout. In the remaining eyes, to dosages of 1 million units, the agent produced no clinically or pathologically evident toxic ocular effects. CONCLUSIONS: Interferon alpha-2b appears to be safe and well tolerated up to dosages of 1 million units.

Animals↗
PubMed1977

The diagnosis of uveal malignant melanomas in eyes with opaque media.

Of 358 eyes enucleated between 1962 and 1975, and found to contain posterior uveal melanomas, 31 had opaque media (8.6%). Eighteen of these patients with opaque media were seen between 1962 and 1971, before the use of combined ultrasonography and the radioactive phosphorus uptake (32P) test. Melanoma was unsuspected at enucleation in one third of these patients and there was often a long delay in diagnosis. Of the 13 patients seen between 1971 and 1975, after the initiation of combined ultrasonography and 32P) test, there was no delay in diagnosis becuase a melanoma pattern was recognized immediately with ultrasonography and confirmed with a positive 32P test. During the latter part of this study, 19 patients with opaque media had a "melanoma pattern" with ultrasonography. The 32P test was positive in 12 cases and a melanoma was confirmed histologically in every instance. The 32P test was negative in seven cases and all were documented on follow-up to have benign lesions, such as subretinal hemorrhages.

Adolescent↗
PubMed1976

Multilobed uveal melanoma masquerading as postoperative choroidal detachment.

A case of multilobed malignant melanoma with a haemorrhagic retinal detachment which mimicked a postoperative choroidal detachment is described. Because the lesion showed no resolution six weeks after cataract surgery a tumour evaluation was undertaken. The diagnosis was established with a positive radioactive phosphorus uptake (32P) test and biopsy of the intraocular mass. A suggested approach to the diagnosis in such difficult cases is proposed.

Aged↗
PubMed1976

B-scan ultrasonography in the diagnosis of atypical retinoblastomas.

Contact B- scan ultrasonography (Bronson-Turner unit) was performed on fourteen patients with retinoblastoma. In ten cases, the patient presented with leukocoria, and ultrasonography was helpful in confirming the clinical diagnosis. In four atypical cases contact B-scan ultrasonography was instrumental in making the diagnosis. The ultrasonographic pattern for retinoblastoma is characteristic but not pathognomic. There is a solid intraocular echo corresponding to the tumor and within it are numerous dense focal echoes which persist at lower sensitivities, suggesting calcification. Calcification was demonstrated ultrasonographically and confirmed histologically in all four of these atypical cases, but routine skull x-rays failed to demonstrate calcium in three of the four children. Contact B- scan ultrasonography is a safe and simple procedure which may provide valuable diagnostic information in children with suspected retinoblastoma.

Calcinosis↗
PubMed1975

Malignant melanomas of the uveal tract in children and young adults.

The Wills Eye Hospital experience with 17 cases of malignant melanoma of the uvea affecting children and young adults was reviewed. They did not appear to differ clinically or histologically from uveal melanomas in older patients, except that in most cases there was a considerable delay in diagnosis, perhaps reflecting a lack of clinical suspicion. Ancillary diagnostic techniques, such as fluorescein angiography, ultrasonography, and 32P studies were often helpful in arriving at the correct diagnosis once the lesion was suspected and referred for evaluation. Malignant melanoma of the uveal tract is not exclusively a disease of old age, and this diagnosis should not be excluded on the basis of the patient's age alone.

Adolescent↗