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Biomedical subjects

W N Clarke

Publications and source records attributed to W N Clarke.

At least 19 recordsLinked to original sources
PubMed1998

Topical versus intravenous administration of tranexamic acid: a comparison of intraocular and serum concentrations in the rabbit.

BACKGROUND: Tranexamic acid has been shown to greatly reduce the incidence of secondary hemorrhage when administered orally or intravenously. Topical administration of the drug should result in much lower serum concentrations, with fewer adverse effects. We performed a study to determine whether topical application of tranexamic acid would yield higher intraocular concentrations and lower serum concentrations of drug than intravenous administration. METHODS: Ten New Zealand white rabbits received 25 mg/kg of tranexamic acid intravenously every 8 hours for 3 days. Another group of 10 rabbits received one drop (0.05 mL) of commercially available tranexamic acid solution (100 mg/mL) every 8 hours for 3 days to one eye. Tranexamic acid levels in the aqueous humour, vitreous humour and serum 1 hour after administration of the last dose of drug were determined. RESULTS: Analysis of variance showed that aqueous concentrations of tranexamic acid were significantly higher with topical delivery than with intravenous administration (15 vs. 9 micrograms/mL)(p < 0.05). Serum concentrations were significantly lower following topical administration (9 vs. 19 micrograms/mL)(p < 0.01). The drug was not detected in the vitreous humour in either group. INTERPRETATION: Topical delivery of tranexamic acid may prove to be valuable in yielding therapeutic intraocular concentrations of drug in patients with hyphema while minimizing systemic toxicity.

Administration, Topical↗
PubMed1995

Air guns: the main cause of enucleation secondary to trauma in children and young adults in the greater Ottawa area in 1974-93.

OBJECTIVES: To determine the proportion of enucleation procedures attributable to injuries from air guns in people aged 18 years or less and to identify the associated pathological findings. DESIGN: Case series. SETTING: Ophthalmic Pathology Registry, University of Ottawa, and affiliated Children's Hospital of Eastern Ontario (Ottawa), Ottawa General Hospital and Ottawa Civic Hospital. In addition, information on air gun injuries from April 1990 to December 1993 was obtained from the Canadian Hospitals Injury Reporting and Prevention Program (CHIRPP) database, with data from 10 pediatric and 5 general hospitals across Canada. PATIENTS: All patients aged 18 years or less who underwent enucleation between Jan. 1, 1974, and Dec. 31, 1993. RESULTS: Eighty-five patients were identified as having undergone enucleation. Trauma accounted for 51 cases (60%), of which 13 (25%) were caused by air guns, the largest single cause of enucleation secondary to trauma. Overall, air gun injuries accounted for 15% of enucleation procedures, whereas retinoblastoma accounted for 21%. All air gun injuries were in boys (median age 14 years, range 9 to 16 years). Of the 13 eyes with air gun injuries 7 had ocular perforation and 6 had ocular penetration. In all cases the intraocular structures were severely disrupted. The CHIRPP database included 165 air gun injuries; 32 were to the eye or ocular adnexa, resulting in 26 hospital admissions. CONCLUSIONS: Air guns were the largest single cause of enucleation secondary to trauma in our study. These guns are widely available in Canada and are unrestricted at muzzle velocities capable of causing death or serious injury, especially to the eye. We feel that air guns should be licensed only to people aged 16 to 18 years or older and that education in their use should be mandatory.

Adolescent↗
PubMed1994

Ocular findings in acromesomelic dysplasia.

We examined an infant who had prenatal onset of a skeletal dysplasia that had many features in common with acromesomelic dysplasia, including the clinical and light and electron microscopic findings of both corneas. Successful lamellar keratoplasty was performed on the left eye when histologic examination of the corneal button from the right eye showed that the corneal scar was only of partial thickness.

Cornea↗
PubMed1993

Brown's syndrome with contralateral inferior oblique overaction: a possible mechanism.

The simultaneous occurrence of Brown's syndrome in one eye and inferior oblique overaction in the other eye is an infrequently reported association. Review of our series of 38 cases of Brown's syndrome disclosed six patients with overaction of the contralateral inferior oblique, of whom four stepped out to contralateral superior oblique palsy. We propose that these patients initially have bilateral Brown's syndrome in infancy, and spontaneous resolution occurs in one eye only. While Brown's syndrome is present the antagonist inferior oblique muscle undergoes isometric contracture. With spontaneous resolution of Brown's syndrome a relative imbalance of forces occurs, with the superior oblique muscle now being relatively paretic compared with the contracted and fibrotic inferior oblique. Up-shoot in adduction then becomes apparent.

Child↗
PubMed1993

Outpatient treatment of microscopic and rim hyphemas in children with tranexamic acid.

Twenty-one patients aged 4 to 15 years with microscopic or rim hyphemas were treated as out-patients with systemic tranexamic acid therapy. The protocol included limited activity at home, topical steroid therapy, no dilating drops, patching for comfort or surface abrasions only, and follow-up every 24 to 48 hours. With this regimen no patient had a secondary hemorrhage. The incidence of associated injuries was surprisingly high, including four patients with angle recession, two with choroidal ruptures and four with commotio retinae, two of whom manifested retinal holes, requiring cryotherapy. We conclude that tranexamic acid therapy decreases the risk of secondary hemorrhage in ambulatory patients with hyphema, but careful assessment and follow-up are necessary to rule out associated ocular injury.

Administration, Oral↗
PubMed1993

Totally asymptomatic inferior oblique overaction.

Seventeen children were demonstrated to have completely asymptomatic overaction of one or both inferior oblique muscles. None had a constant vertical deviation in primary position, up gaze or down gaze, and significant patterns were absent. None had diplopia or complaints of torsion. The Bielschowsky head tilt test gave a negative result in all cases. No patient showed excyclorotation on fundus examination. Long-term follow-up (28 to 134 [average 75.6] months) of 13 of the patients showed that the condition did not worsen with time and may not require surgical weakening of the inferior oblique muscle.

Adolescent↗
PubMed1992

Oral administration of tranexamic acid in the management of traumatic hyphema in children.

In a prospective study 163 patients aged 17 years or less admitted to a children's hospital between April 1985 and December 1990 with traumatic hyphema were treated with tranexamic acid, 25 mg/kg given orally every 8 hours to a maximum of 1500 mg every 8 hours for 5 days. Secondary hemorrhage occurred in 5 patients (3%), none of whom had more than one rebleeding episode. In contrast, 24 (8%) of 316 patients aged 17 years or less admitted to the same hospital between January 1977 and March 1985 with traumatic hyphema who were not treated with antifibrinolytics had a secondary hemorrhage, several more than once, giving a rebleeding rate of 33/316 (10%). The results suggest that tranexamic acid reduces the incidence and number of secondary hemorrhages in children, without significant ocular or systemic side effects.

Administration, Oral↗
PubMed1990

Limbal lensectomy in the management of ectopia lentis in children.

Surgical treatment of ectopia lentis has traditionally been associated with a poor visual outcome and a high complication rate. We treated a series of nine children (15 eyes) whose visual acuity could not be improved with optimal optical phakic or aphakic correction with limbal lensectomy. Preoperative visual acuity after amblyopia treatment ranged from 20/60 to 20/200. Improvement in postoperative visual acuity was documented in all operated-on eyes, ranging from 20/20 to 20/50 during a follow-up period ranging from 8 months to 118 months (median, 33 months). The only complication was a child who developed a secondary membrane requiring a neodymium-YAG capsulotomy.

Child↗
PubMed1990

Clinical management of orbital cellulitis in children.

A prospective study was carried out by the Department of Ophthalmology and the Division of Infectious Disease at the Children's Hospital of Eastern Ontario to assess the outcome of our medical management of orbital cellulitis in children using a predetermined antibiotic regimen and to determine whether computed tomographic (CT) evidence of a subperiosteal abscess alone was an indication for surgical drainage. Between February 1985 and January 1988, 23 patients with true orbital cellulitis were admitted. CT scans were ordered routinely at the time of admission. The scans were cancelled for 13 children because they responded rapidly to medical management. CT showed edema nasal to the medial rectus, or thickening or displacement of the muscle in 8 of the 10 children who underwent the procedure. Three children required sinus and orbital drainage, but frank purulent material was found subperiosteally in only one. The results suggest that most children with orbital cellulitis can be managed with the prompt use of the appropriate intravenous antibiotics. Therapy with cloxacillin sodium and chloramphenicol or, in children under age 6 years, cefuroxime best covers the spectrum of organisms responsible for most cases of orbital cellulitis in children. CT should be used as an ancillary guide to the need for surgical exploration of the orbit in patients who do not rapidly respond to medical management.

Abscess↗
PubMed1988

Rotatory nystagmus in infantile esotropia.

We reviewed the charts of 119 children with infantile esotropia followed for 27 months to 16 years (average 82.5 months). Of the 119, 14 (12%) had fine (high frequency, low amplitude) rotatory nystagmus. The presence of the nystagmus may account for a decline in visual acuity of up to two lines under binocular viewing conditions.

Amblyopia↗
PubMed1988

Intraocular pressure reduction prior to retrobulbar injection of anesthetic.

Following the retrobulbar injection of anesthetic, the application of a mechanical device to lower the intraocular pressure will produce a rise in intraocular pressure that may be sufficient to compromise ocular perfusion. To increase the margin of safety for ischemic damage, a mechanical means of intraocular pressure reduction (Superpinkie) was applied prior to, rather than following, the retrobulbar injection of anesthetic. The study group consisting of 20 patients receiving the compression-injection sequence had a mean preoperative pressure of 4.70 mm Hg, while a control group of 20 patients receiving the injection-compression sequence had a mean preoperative pressure of 2.25 mm Hg. The proposed compression-injection method was well tolerated by the patients and attained surgically adequate anesthesia, akinesia, and ocular opening pressures. In selective cases, the compression-injection technique for the delivery of retrobulbar anesthesia may offer a means of better maintaining ocular perfusion and thereby lessening the risk of vascular compromise.

Anesthesia, Local↗