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Biomedical subjects

K W Wright

Publications and source records attributed to K W Wright.

At least 19 recordsLinked to original sources
PubMed1992

Results of late surgery for presumed congenital cataracts.

We reviewed the results of cataract extraction and visual rehabilitation in 76 eyes of 47 infants and children with presumed congenital cataracts who were first seen after they were 10 months old. Eighteen patients underwent surgery for unilateral cataracts, including five patients with persistent hyperplastic vitreous, five with posterior lenticonus, one with a nuclear cataract, six with posterior subcapsular cataracts, and one with a lamellar cataract. Of these 18 patients, seven (39%) attained a visual acuity of 20/60 or better, one (6%) had a visual acuity of 20/100, and ten (60%) had a visual acuity of 20/200 or worse. Twenty-nine patients (62 eyes) underwent bilateral cataract extraction. The visual acuity could be measured in 22 patients (44 eyes). Visual acuity improved to 20/60 or better in 32 eyes (73%), was between 20/70 and 20/150 in 11 eyes (25%), and became worse than 20/200 in one eye (2%). Results were good in patients with persistent hyperplastic primary vitreous, posterior lenticonus, and bilateral cataracts.

Adolescent↗
PubMed1992

Binocular fusion and stereopsis associated with early surgery for monocular congenital cataracts.

Despite improved visual acuity results in infants undergoing early surgery for monocular congenital cataracts, virtually all reports indicate a lack of binocular vision and the presence of strabismus in these patients. We report herein the presence of motor fusion and stereopsis in patients who have undergone early surgery for monocular congenital cataracts. Of 13 patients with congenital cataracts who were operated on by age 9 weeks, five (38%) had essentially straight eyes and evidence of motor fusion with a minimum of 1 year of follow-up. Three (60%) of five patients demonstrated sensory fusion, two with Titmus testing and one with Randot Stereo Acuity (Stereo Optical Co Inc, Chicago, Ill) of 250 seconds of arc. We conclude that binocular fusion and stereo visual acuity are obtainable in patients with monocular congenital cataracts.

Cataract↗
PubMed1992

Third nerve palsy due to cerebral artery aneurysm in a child.

We report a case of cerebral aneurysm in a seven-year-old girl who presented with subacutely progressive third nerve palsy. To our knowledge this is the youngest reported patient with this condition. Confusion with myasthenia gravis occurred because of improvement in the patient's ptosis after intravenous edrophonium chloride. Cerebral CT revealed a hyperdense mass that was characterised on cerebral angiography as an aneurysm of the posterior communicating artery. Another occult aneurysm of the posterior cerebral artery was found at surgery. This case demonstrates that third nerve palsy due to cerebral aneurysm may affect patients at a younger age than has previously been recognised. Therefore we suggest that even young children should have aneurysm excluded by cerebral CT and angiography if they present with acquired third nerve palsy involving the pupil. In addition this case highlights the false-positive results that may occur with the edrophonium chloride test for myasthenia gravis.

Blepharoptosis↗
PubMed1991

Conjunctival retraction suture for fornix adjustable strabismus surgery.

The fornix approach to strabismus surgery is advantageous because the incision is made under the eyelid, there is no need for conjunctival sutures, it is comfortable for the patient, and there is minimal postoperative scarring. The major disadvantage of the fornix approach for the adjustable suture technique has been poor exposure to the muscle-suture apparatus and poor postoperative knot exposure. We describe herein the use of a subconjunctival retraction suture for adjustable suture surgery with the fornix approach. This suture retracts the conjunctiva, exposing the adjustable muscle-suture apparatus while simultaneously fixating the globe. A novel way of tying the noose around the pole sutures and preventing noose slippage is also presented. This technique provides excellent exposure, fixation of the globe, and complete coverage of the knot with conjunctiva after adjustment.

Conjunctiva↗
PubMed1991

Hereditary lymphedema and distichiasis.

Two patients with lymphedema-distichiasis syndrome illustrate that both Milroy's disease and late-onset hereditary lymphedema are sometimes associated with distichiasis. It is important for ophthalmologists to be aware of the lymphedema-distichiasis syndrome because of its ophthalmic manifestations and the associated systemic abnormalities that can be potentially life threatening.

Adolescent↗
PubMed1991

Effect of a modified rectus tuck on anterior ciliary artery perfusion.

Strabismus surgery results in the permanent interruption of anterior ciliary blood flow, predisposing the eye to anterior segment ischemia (ASI). A primate model was used to assess the effectiveness of a new muscle-scleral tuck for preserving anterior ciliary artery circulation. The model consisted of removing 3 rectus muscles from both eyes of 2 rhesus monkeys, then performing a tuck on the inferior rectus (IR) right eye while leaving the left IR as a control. Four weeks later, a modified tuck was performed on the virgin left IR. Fluorescein iris angiograms of both eyes were obtained, and preoperative angiograms at 5-15 sec. showed normal 360 degrees perfusion. Postoperative follow-up angiograms showed segmental superior temporal filling defects and preservation of perfusion in the distribution of the IR. Comparison of fellow eyes tucked vs control IR showed no difference in the filling pattern in both monkeys. Comparison of the same eye before and after tuck also showed essentially the same filling pattern in all 4 eyes with preservation of inferior circulation. Our conclusion is that the modified tuck preserves the anterior ciliary blood flow and may be useful as a muscle-strengthening procedure in patients predisposed to developing ASI.

Animals↗
PubMed1990

Automated perimeter for binocular suppression.

Scotomas associated with suppression amblyopia can appear or enlarge under binocular conditions. A device was designed to present an independent LED stimulus array to each eye while both eyes fixate together through beam splitters on a common background pattern. A computer-controlled field screening examination was designed to automatically plot suppression scotomas under binocular conditions.

Amblyopia↗
PubMed1989

Nucleotide-free kinesin hydrolyzes ATP with burst kinetics.

Bovine brain kinesin binds ADP tightly and contains a stoichiometric amount of ADP at its active site when isolated in the presence of free Mg2+ (Hackney, D. D. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 6314-6318). EDTA in excess of Mg2+ weakens ADP binding and nucleotide-free kinesin can be prepared by gel filtration with excess EDTA. On addition of ATP, this nucleotide-free enzyme catalyzes the rapid hydrolysis of a stoichiometric amount of ATP in a burst phase followed by much slower continued ATP hydrolysis limited by the release of ADP from the active site. This burst reaction is evident both by formation of [32P]Pi from [gamma-32P]ATP and by formation of [alpha-32P]ADP from [alpha-32P]ATP. At 1.1 nM kinesin active sites, the observed rate of the burst phase increases linearly with ATP over the 1-20 nM range yielding a bimolecular rate of net ATP binding and hydrolysis of 2.5 microM-1 s-1. The intercept at zero ATP is 0.008 s-1 which equals the ADP release rate at 0.008-0.009 s-1. This predicts a Km for ATP of approximately 3.5 nM and measurements of the dependence on ATP concentration of the steady state rate and amount of bound ADP are consistent with a Km of this magnitude.

Adenosine Triphosphatases↗
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↗
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↗