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Biomedical subjects

C A McKeown

Publications and source records attributed to C A McKeown.

At least 19 recordsLinked to original sources
PubMed1998

Tonometry in adults and children. A manometric evaluation of pneumatonometry, applanation, and TonoPen in vitro and in vivo.

OBJECTIVE: The purpose of the study was to determine the accuracy of applanation tonometry, pneumatonometry, and TonoPen tonometry in adults and children and the effect of age on tonometer error. DESIGN: The design was divided into four parts: part 1 was prospective and cross-sectional, and parts 2 through 4 were prospective, cross-sectional, and masked. PARTICIPANTS: This study contained 72 patients representing 74 data points. INTERVENTION: Tonometry with simultaneous manometry was performed. MAIN OUTCOME MEASURES: Intraocular pressure (i.o.p.) and the tonometric estimate of IOP were obtained. RESULTS: The normal pediatric IOP follows the line Ta = 0.71 age(years) + 10 up to age 10. Applanation tonometry under anesthesia differs from pneumatonometry by an average of -8.6 mmHg and is age related by the equation Ta = Tpn + 2.6 log(age) - 10.3. The TonoPen was the most accurate instrument for enucleated eyes, and the pneumatonometer was the most accurate in anesthetized living eyes. CONCLUSIONS: Applanation tonometry markedly underestimated IOP in young eyes. TonoPen tonometry performed well with enucleated eyes but was not adequately accurate for clinical use. The pneumatonometer performed the best clinically and the best overall.

Adolescent↗
PubMed1997

Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles.

Congenital fibrosis of the extraocular muscles is an autosomal dominant congenital disorder characterized by bilateral ptosis, restrictive external ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position, and markedly limited and aberrant residual eye movements. It has been generally thought that these clinical abnormalities result from myopathic fibrosis of the extraocular muscles. We describe the intracranial and orbital pathology of 1 and the muscle pathology of 2 other affected members of a family with chromosome 12-linked congenital fibrosis of the extraocular muscles. There is an absence of the superior division of the oculomotor nerve and its corresponding alpha motor neurons, and abnormalities of the levator palpebrae superioris and rectus superior (the muscles innervated by the superior division of the oculomotor nerve). In addition, increased numbers of internal nuclei and central mitochondrial clumping are found in other extraocular muscles, suggesting that the muscle pathology extends beyond the muscles innervated by the superior division of cranial nerve III. This report presents evidence that congenital fibrosis of the extraocular muscles results from an abnormality in the development of the extraocular muscle lower motor neuron system.

Abnormalities, Multiple↗
PubMed1997

Accumulation of Diplostomum spp. (Digenea: Diplostomatidae) metacercariae in the eyes of 0+ and 1+ roach (Rutilus rutilus).

Unlike other long-term studies of Diplostomum spp. metacercariae in fish eyes, this study investigated accumulation of the parasites in the eyes of very young roach for 3 consecutive years. Fish were caught by electro-fishing in the summers of 1990, 1991 and 1992 and the numbers of parasites located in the hosts eyes were recorded. Two distinct peaks of parasite abundance were observed, 1 in late June and the other in mid-September each year. Significantly, parasite abundance decreased after each of the peaks. Results obtained in a parallel investigation of the accumulation of the same parasites in rainbow trout in an adjacent fish farm showed the same 2 periods of accumulation each year. However, in the fish farm, no decrease in parasite abundance was observed at any time. The decreases in parasite abundance in the wild population can be attributed to mortality of the most heavily parasitized fish. As this did not occur in the farmed fish, in which similar levels of parasitism existed, it is likely that mortality in the wild population was an indirect result of the parasites.

Animals↗
PubMed1995

The life cycle stages of three Diplostomum species maintained in the laboratory.

The taxonomy of Diplostomum species is in a highly confused state due to synonomy and descriptions based on only one life cycle stage. The objective of this study was to establish and maintain life cycles of several Diplostomum species in the laboratory so that accurate and detailed descriptions could be made. Metacercariae taken from the eyes of fresh water fish were identified using the key of Shigin (1986). Adopting the method of Field, McKeown & Irwin (1994) life cycles of Diplostomum spathaceum, Diplostomum parviventosum and Diplostomum volvens were established and each stage was described, measured and photographed or illustrated as required. The results of this work will provide standard descriptions for the life cycle stages of these Diplostomum species. It will relieve some of the identification difficulties experienced when only one stage in the life cycle is encountered.

Animals↗
PubMed1995

The use of propofol and mivacurium anesthetic technique for the immediate postoperative adjustment of sutures in strabismus surgery.

PURPOSE: Adjustable suture techniques have become increasingly popular over the last decade and may reduce the re-operation rate after strabismus surgery. The adjustment usually is made in the hospital or office 5 to 24 hours after surgery, when the patient has fully recovered from general anesthesia. The ability to perform suture adjustment in the operating room, immediately after completion of surgery, would be an attractive alternative with respect to patient monitoring, sterility, comfort, and timing. The purpose of this study is to compare the alignment of patients in the operating room adjusted immediately after surgery with their alignment the morning after surgery. METHODS: Patients with strabismus who have good vision in each eye and who were judged to be appropriate candidates for adjustable sutures were invited to enroll in a study using propofol and mivacurium total intravenous anesthetic technique. Patients underwent strabismus surgery in which one or more muscles were placed on adjustable sutures. Immediately after extubation, these patients were awakened in the operating room, assisted in sitting upright, and asked to fixate on a 20/400 Snellen E target on the operating room wall. Sutures were adjusted, when necessary, to obtain the desired postoperative alignment. Prism and alternate cover measurements, taken after the sutures were permanently tied, were compared with measurements taken the morning after surgery. RESULTS: Twenty-nine patients qualified for inclusion. Measurements of horizontal and vertical alignment in the operating room were all within 12 prism diopters (PD) of the measurements taken 18 to 24 hours after surgery (mean variation, 4 PD horizontally and 2 PD diopters vertically). The measured deviation changed less than or equal to 6 PD horizontally in 78% of patients and less than or equal to 3 PD vertically in 70% of patients. CONCLUSION: For some adult patients with strabismus, a total intravenous general anesthesia technique using an infusion of propofol and mivacurium may provide the opportunity for accurate suture adjustment in the operating room, immediately after completion of surgery.

Adolescent↗
PubMed1993

Effect of severing the check ligaments and intermuscular membranes on medial rectus recessions in infantile esotropia.

BACKGROUND: The effect of severing the check ligaments and intermuscular membranes on the dose-response curve for medial rectus recessions in patients with infantile esotropia has not been previously studied by randomized assignment techniques using contemporary control and experimental groups and masked precautions. METHODS: A prospective study of 101 patients was performed over an 8-year period. Patients were randomly assigned to either augmented or nonaugmented groups. In the former group, the medial check ligaments and intermuscular membranes were severed; in the latter group, no surgery was performed on the medial check ligaments or intermuscular membranes. Patients were postoperatively evaluated by an observer masked to group assignment. RESULTS: No difference in response to surgery was observed between the two groups at the time of evaluation, which took place, on average, 6 to 7 months after surgery. CONCLUSION: Severing the check ligaments and intermuscular membranes on patients with infantile esotropia undergoing medial rectus recessions does not appear to affect the dose-response curve.

Adolescent↗
PubMed1992

Amblyopia.

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Amblyopia↗
PubMed1992

Duane's syndrome.

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Age Factors↗
PubMed1992

Brown's syndrome.

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Cranial Nerve Diseases↗
PubMed1989

Preservation of the anterior ciliary vessels during extraocular muscle surgery.

Conventional, full-tendon, rectus muscle surgery disrupts the anterior ciliary vessels. This may lead to anterior segment ischemia when the number of interrupted vessels is sufficient to significantly compromise anterior segment blood flow. Clinical observations and histologic studies provide new anatomic information concerning the course of the anterior ciliary vessels in the sub-Tenon's region. These studies demonstrate the feasibility of dissection and preservation of the anterior ciliary vessels during rectus muscle surgery. Dissection and preservation of 35 clinically apparent anterior ciliary vessel groups were attempted on 15 rectus muscles during strabismus surgery. The unplanned vessel destruction rate was 9.5%. Procedures included 12 recessions, 1 resection, and 2 full-tendon transpositions. The possible role of this procedure in the prevention of anterior segment ischemia is discussed.

Adolescent↗
PubMed1985

Trilateral retinoblastoma: ocular and pineal retinoblastomas.

Trilateral retinoblastomas, the syndrome of bilateral retinoblastoma associated with ectopic retinoblastoma in the pineal gland, is rare but well recognized. In contrast to bilateral retinoblastomas alone, the ocular retinoblastomas in trilateral retinoblastoma develop before the age of 6 months, and a family history positive for retinoblastoma is usually obtained. The retinal tumors are often quiescent at the time that the pineal tumor is discovered, and show no evidence of metastatic spread after enucleation of the globes. Pathologically, the pineal tumor is indistinguishable from the ocular retinoblastoma. The pathophysiology of this syndrome is not well understood, but a germinal mutation is thought to target photoreceptor tissue for further postzygotic mutation. Eventual expression depends on the inherited host resistance to the carcinogenic manifestation of these genes. The low host resistance of trilateral retinoblastoma is evident by the early age of presentation, the multicentric occurrence of the tumor, and the high early mortality rate despite aggressive management.

Brain Neoplasms↗
PubMed1982

Juvenile xanthogranuloma of the optic nerve, disc, retina, and choroid.

A 20-month-old infant found to have a blind eye with neovascular glaucoma was thought to have a neoplasm of the optic nerve for which enucleation was performed with resection of a long segment of optic nerve. Microscopic examination revealed the enlarged optic nerve and optic papilla to be infiltrated densely by histiocytic cells, including Touton giant cells, all containing large amounts of neutral fat. The histologic picture was indistinguishable from that of juvenile xanthogranuloma. Occlusion of the central retinal vessels had led to hemorrhagic infarction of the retina and neovascular glaucoma. Thorough clinical and laboratory investigations repeated over a period of more than 2 1/2 years failed to disclose any evidence of a systemic disease, and the child has remained in good health. This is believed to be a unique case of juvenile xanthogranuloma of the optic nerve and disc.

Child, Preschool↗
PubMed1981

Tamoxifen retinopathy.

A 63-year-old female on long-term, high-dose tamoxifen treatment for metastatic breast cancer developed bilateral intraretinal refractile opacities, lesions at the level of the retinal pigment epithelium, and cystoid macular oedema.

Breast Neoplasms↗