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Biomedical subjects

K W Wright

Publications and source records attributed to K W Wright.

At least 55 records · Page 3Linked to original sources
PubMed1987

Congenital ocular motor apraxia in twins. Findings with magnetic resonance imaging.

A pair of identical twins, whose features met Cogan's classic description of congenital ocular motor apraxia, were examined. Each had an absence of willed horizontal saccades and demonstrated classic head thrusting. Magnetic resonance imaging revealed hypoplasia of the corpus callosum. Fourth ventricle enlargement and generalized cerebral hypoplasia were also present but were more pronounced in the sibling with the more delayed motor development. The significance of these findings is discussed in light of our understanding of the control mechanism of volitional eye movements.

Agenesis of Corpus Callosum↗
PubMed1986

Reliability of fixation preference testing in diagnosing amblyopia.

We evaluated the sensitivity and specificity of standard fixation preference testing and the 10-prism diopter (PD) fixation test in 427 patients. Standard fixation preference testing showed good sensitivity and specificity for than 10 PD. Patients with small angle tropias, however, had a high false-positive rate, with 40% of nonamblyopic patients inappropriately responding with strong fixation preference. The 10-PD fixation test reduced this high false-positive rate and showed only 1.5% false-positive results. Unfortunately, this shift to equal fixation preference was also seen in some patients with amblyopia, as five of 19 patients with three or more lines difference alternated fixation with the 10-PD fixation test. Retesting disclosed that, although these children would briefly alternate to the amblyopic eye while viewing a stationary target, they would not hold fixation with the amblyopic eye through smooth pursuit. Our conclusion is that standard fixation preference testing can be used to diagnose moderate to severe amblyopia in patients with tropias greater than 10 PD. Patients with small angle deviations or straight eyes should be examined with the 10-PD fixation test, with the criterion for equal vision being the ability to hold fixation well with either eye through smooth pursuit.

Amblyopia↗
PubMed1986

Recording pattern visual evoked potentials under chloral hydrate sedation.

Accurate assessment of visual function in infants and preverbal children is difficult because of the dependence on vision tests that require the patient's cooperation. In an attempt to resolve this problem, we evaluated pattern visual evoked potentials (PVEPs) obtained on infants under chloral hydrate sedation. Ten patients were studied--four with unilateral amblyopia, three with suspected amblyopia, and three without amblyopia. Patients with amblyopia showed robust and reproducible responses from the sound eye, while responses from the amblyopic eye were significantly diminished (amplitude ratio less than or equal to 0.63). The PVEP responses from patients without amblyopia were large in amplitude and symmetrical between fellow eyes (amplitude ratio greater than 0.9). In two eyes with normal vision, optically fogging the patterned stimulus image substantially reduced the PVEP response, establishing a sensitivity to pattern images rather than changes in the overall luminance. We have thus determined that the PVEP can be reliably obtained under chloral hydrate sedation and that these responses, like PVEP responses taken in the awake state, reflect the presence of amblyopia and image clarity. Use of the PVEP with chloral hydrate sedation may prove clinically useful for detecting amblyopia in uncooperative infants and children.

Amblyopia↗
PubMed1986

P100 amplitude variability of the pattern visual evoked potential.

This study quantifies the amplitude variability of the pattern visual evoked potential (P-VEP) and compares this variability between the two eyes and between individual runs recorded in the typical clinical laboratory. Cooperative adults were studied in order to obtain measurements under optimal conditions. Average P100 amplitudes of 10 runs for one eye were essentially equal to average P100 amplitudes of the other eye, as were the variances. Mean amplitude ratio (the smaller amplitude divided by the larger amplitude) was 0.91. With a group mean P100 amplitude of 10.06 microV, standard deviation for intrasubject data was 1.84, and for intersubject data was 3.75. Therefore, most of the amplitude variability between the two eyes is due to run-to-run variability. A minimum of 3 runs (100 stimuli each) and an optimum of 5 runs should be recorded before making an evaluation.

Adult↗
PubMed1986

The fat adherence syndrome and strabismus after retina surgery.

The etiology of persistent strabismus after retina surgery has been poorly understood. Seven patients with acquired restrictive strabismus after retina surgery were surgically explored for the cause of the strabismus. In each case, the fat adherence syndrome was identified as playing a significant role in causing the restriction. In four patients, restriction secondary to the fat adherence syndrome was the sole cause of the strabismus. Other contributing causes included a misplaced muscle in two patients and a sponge under a muscle in one patient. Our conclusion is that the fat adherence syndrome is an important cause of restrictive strabismus after retina surgery and that this complication can be minimized by avoiding surgical maneuvers that violate Tenon's capsule and expose extraconal fat.

Adipose Tissue↗
PubMed1985

Implant-induced trabecular damage in cadaveric femoral necks.

After insertion of Newman's pins, Smith-Petersen nails and compression hip screws into human cadaveric proximal femora, the area of trabecular damage was measured. The nail and hip screw caused four times the area of damage seen with Newman's pin. The Smith Petersen nail caused significant peripheral damage which was undetectable radiographically.

Bone Nails↗
PubMed1982

Acquired inflammatory superior oblique tendon sheath syndrome. A clinicopathologic study.

To our knowledge, this is the first reported clinicopathologic study of a patient with acquired inflammatory Brown's syndrome. The superior oblique tendon, trochlea, and anterior superior oblique muscle were surgically removed en bloc and studied by light microscopy. Surprisingly, the entire specimen was normal, without signs of inflammation or intrasheath scarring. The only abnormal finding was found during surgery, which consisted of perisheath adhesions anterior to the trochlea. These findings indicate that the cause of acquired inflammatory Brown's syndrome may, in many cases, be from scarring around the tendon sheath rather than an intrasheath pathologic condition, as proposed by recent literature.

Female↗
PubMed1982

Wear studies on prosthetic materials using the pin-on-disc machine.

The wear of ultra high molecular weight polyethylene in combination with cobalt-chromium-molybdenum alloy was investigated by pin-on-disc experiments in which the alloy pin was loaded against the rotating polyethylene disc. In some experiments the pin was stationary, but in others it rotated about its axis. The effect of lubricant type, pin rotation, magnitude of the applied load, magnitude of the relative surface velocity, and disc storage in various environments was investigated. Wear of the polyethylene was assessed at 100 h intervals by both volumetric and gravimetric methods. Each experiment lasted 1000 h. It was concluded that of the lubricants tested bovine serum was the most suitable and that pin rotation produced more suitable polyethylene surfaces than did the stationary pin. The wear rate increased slightly with load (possibly owing to creep), was insensitive to speed, and was not affected by disc storage. The dynamic coefficient of friction increased with running tme. Results obtained by the two wear assessment methods were comparable and the reproducibility of the results was good.

Animals↗
PubMed1981

10-Diopter fixation test for amblyopia.

Fixation-preference testing has been useful in detecting amblyopia in children unable to give reliable visual acuities, except for children with small-angle tropias and those without manifest deviations. This study introduces a method of fixation testing that includes all children, regardless of the presence or size of the deviation. By placing a 10-diopter vertical prism over one eye, we induce a vertical deviation. Once the eyes are dissociated, fixation preference is evaluated and used to predict the presence of amblyopia. We prospectively studied fixation patterns in 98 children with either small-angle tropia or essentially straight eyes. All children with amblyopia of two lines or more showed abnormal fixation patterns, and those without amblyopia showed normal patterns. We were able to obtain fixation patterns on all children studied, including 13 infants less than 24 months of age. This test proved to be a reliable, objective method for detecting amblyopia in children with straight eyes or in children with microstrabismus of almost any age.

Adolescent↗
PubMed1980

Dependence of stem stress in total hip replacement on prosthesis and cement stiffness.

Two dimensional finite element analyses were used to determine the direct tensile stress distributions along the lateral edge of the stem of the femoral component of a total hip replacement. The efficacy of using two-dimensional analysis for three-dimensional composite structures was assessed, and the two-dimensional model was found to be suitable for parametic studies. Various combinations of stem and cement stiffnesses were investigated. In particular the influence of stem taper, cement stiffness, prosthesis stiffness and the effect of a plateau on the prosthesis stresses, were examined and compared. The most significant factor was found to be the modulus of elasticity of the stem material. The tensile stresses decrease with decreasing modulus. Cement stiffness and stem shape appeared to have far less effect on stem stress.

Bone Cements↗
PubMed1980

The Monk "soft top" endoprosthesis. Clinical, biomechanical and histopathological observations.

This paper presents a prospective trial carried out using the Monk "soft top" endoprosthesis in 33 patients. Two years after operation 70 per cent of the remaining patients had pain. A biomechanical and histopathological analysis of the endoprosthesis and the surrounding tissue, obtained from a further two patients at the time of revision, is presented. It is concluded that the prosthesis has inherent design faults which result in excessive wear of the polyethylene component. The wear debris produced stimulates a prolific fibrous tissue reaction which is associated with progressive clinical deterioration.

Aged↗
PubMed1979

Reactive force distributions for teeth when loaded singly and when used as fixed partial denture abutments.

1. A finite element model was devised to examine mechanical responses of the periodontium to loads applied to the model in vertical, oblique, and horizontal directions for an individual tooth having varied alveolar levels, splinted teeth, and a cantilever type of fixed partial denture. 2. Forces applied to the teeth are balanced by stresses generated within the periodontal membrane and alveolar bone. 3. It was substantiated that the teeth were evolved to carry axial types of loads, since stresses on the periodontium were smaller than those obtained for oblique or horizontal types of loads. Axial types of loads produce compressive stresses on the periodontium; oblique or horizontal types of loads produce zones of compressive and tensile stresses. 4. Mechanically, splinting teeth is a desirable procedure. 5. A cantilever type of fixed partial denture should have at least two abutments. It should not be used to replace more than one tooth.

Alveolar Process↗
PubMed1979

An analytical investigation into possible mechanical causes of bone remodelling.

Three-dimensional finite element analyses were carried out on idealisations of two situations where bone remodelling has been reported clinically viz. the malaligned femur and a maxillary central incisor under orthodontic loading. The mechanical responses, i.e. stress, strain and change of curvature, in various directions, are presented. They are compared with the biological response, either bone resorption or bone deposition. The results are discussed in relation to three current theories of bone remodelling.

Alveolar Process↗
PubMed1979

Biomechanics of the femoral component of total hip prostheses with particular reference to the stress in the bone-cement.

Two-dimensional finite element analyses were used to determine the normal and shear stress distributions at the prostheses-cement and cement-bone interfaces in the femoral component of a total hip replacement. Various combinations of stem, cement and bone stiffnesses were investigated. In particular the influences of stem taper, cement stiffness, prosthesis stiffness and the effect of a plateau, on the cement stresses were examined and compared. It was particulary noticeable that the normal direct stress across the cement in the proximal region of the stem, both literally and medially, as generally compressive. It was found that the more flexible the cement the more uniform were the stress distributions. Furthermore, these stresses increase as the stiffness of the stem decreases.

Biomechanical Phenomena↗