Search PubMed⌕ Search

Biomedical subjects

D G Hunter

Publications and source records attributed to D G Hunter.

34 records · Page 2Linked to original sources
PubMed1995

Inferior oblique muscle injury from local anesthesia for cataract surgery.

BACKGROUND: Vertical rectus muscle injury is commonly cited as a cause of strabismus after cataract surgery. Injury to the inferior oblique muscle or nerve as a complication of cataract surgery has not been described previously. METHODS: Four patients without pre-existing strabismus who had diplopia after cataract surgery were studied. Analysis included prism and cover testing, Lancaster red-green testing, and fundus torsion assessment. RESULTS: Three patients had a delayed-onset hypertropia with fundus extorsion in the eye that underwent surgery, which is consistent with inferior oblique muscle overaction secondary to presumed contracture. The fourth patient had an immediate-onset hypotropia with fundus intorsion in the eye that underwent surgery, which is consistent with inferior oblique muscle paresis. Damage to a vertical rectus muscle or "unmasking" of a pre-existing superior oblique muscle paresis could not explain the history and findings in this group of four patients. CONCLUSION: The inferior oblique muscle contracture observed in three patients may have been caused by local anesthetic myotoxicity, whereas the paresis observed in one patient may have been due to mechanical trauma or anesthetic toxicity directly to the nerve innervating the muscle. Inferior oblique muscle or nerve injury should be considered as another possible cause of postoperative strabismus, especially when significant fundus torsion accompanies a vertical deviation.

Aged↗
PubMed1993

Diode laser photocoagulation for threshold retinopathy of prematurity. A randomized study.

BACKGROUND: Although peripheral cryotherapy decreases the incidence of unfavorable anatomic outcomes in threshold retinopathy of prematurity (ROP), apnea, bradycardia, and lid edema can occur. Argon laser indirect ophthalmoscope photocoagulation has been used as an alternative to cryotherapy, with fewer adverse effects. Retinal lesions placed with diode lasers are deeper than similar argon laser lesions, and it is not known whether this difference could influence the response to ablative therapy. METHODS: Patients were enrolled under a prospective, randomized protocol. One eye of each patient with symmetric, threshold ROP was treated with an 814/815 nm diode laser, while the other eye was treated with cryotherapy. Patients with asymmetric diseases also were randomized for treatment in the threshold eye. RESULTS: Nineteen infants (33 eyes) were treated, ranging from 485 to 863 g birth weight (23 to 27 weeks gestational age); 18 patients (32 eyes) were followed for 3 months or longer. Four patients (8 eyes) had bilateral zone 1 disease. Postconceptional age was 36 to 45 weeks at the time of treatment. The diode laser treatment was better tolerated than cryotherapy, and the treatment apparatus was more easily transported. Apneic episodes requiring intubation resulted from two cryotherapy sessions but no diode laser sessions. Five cryotherapy-treated eyes required retreatment because of persistent disease with adjacent skip areas. In the group followed for 3 to 15 months, 1 cryotherapy-treated eye and 1 diode laser-treated eye progressed to stage 5 retinal detachment. CONCLUSION: Compared with cryotherapy, the diode laser was more convenient, technically easier to administer, and better tolerated by the patient. Although the number of patients was too small for meaningful statistical analysis of outcome, diode laser peripheral retinal ablation appeared to be as effective as cryotherapy for the treatment of threshold ROP.

Cryosurgery↗
PubMed1988

Abnormal axonemes in X-linked retinitis pigmentosa.

Sperm of patients with X-linked retinitis pigmentosa (RP) was studied to assess the state of the axoneme in this genetic subtype. Semen samples were collected from eight patients with X-linked RP and compared with a database of 31 controls. Semen was also collected from two patients with other retinal degenerations (choroideremia and fundus flavimaculatus) and patients with simplex RP. All controls and patients were studied under a masked protocol. There was a significant increase in the percentage of abnormal sperm tails at both the light and electron microscopic levels in patients with X-linked RP only. Thus, X-linked RP is associated with an alteration in sperm axoneme structure. Sperm cell analysis may serve as a useful model system for additional investigations into the pathogenesis of this disease.

Adult↗
PubMed1986

Abnormal sperm and photoreceptor axonemes in Usher's syndrome.

Axonemes are organelles that are composed of microtubule doublets and singlets with a complex assembly of associated proteins. This study was designed to investigate the possibility that an abnormal axoneme is involved in the pathogenesis of Usher's syndrome. A masked structural and functional analysis of sperm was performed on samples from ten patients with Usher's syndrome and 33 controls, including duplicate samples from six patients and three controls. In the functional analyses, there was a significant decrease in patient sperm motility and velocity. Structurally, there was a significant increase in tail abnormalities at both the light and electron microscopic levels. Ejaculate volume and sperm concentration were normal in the patient population. The presence of abnormal axonemes was also confirmed in remnant photoreceptors of a whole eye donation from a patient with Usher's syndrome. The data suggest that defective connecting cilia axonemes may be involved in the irreversible, progressive loss of photoreceptors in Usher's syndrome.

Adult↗
PubMed1986

Abnormal axonemes in sperm of fertile men.

Sperm of 20 men aged 20-44 years was analyzed for motility and tail deformities in a Makler chamber and for axoneme abnormalities by transmission electron microscopy. In the quantitative analyses, 12.5 +/- 5.5% deformed tails at the light microscopic level and 24.4 +/- 7.7% abnormal axonemes in the principal piece. This high incidence of abnormalities in the sperm of fertile men indicated that micrographs of abnormal axonemes alone could not be used to imply the pathogenesis of infertility or sperm immotility without statistical comparison with a control group. Axoneme abnormalities were subdivided into three types. There was an asymmetry of abnormal axoneme types along the length of the sperm tail. Based on this asymmetry and on images of longitudinally sectioned sperm, the different types of abnormal axonemes most likely represented a single process of doublet microtubule detachment and foldback. Correlation of electron and light microscopy suggested that axoneme foldback progressed to focal tail defects and subsequent collapse. The presence of these abnormalities in fertile donors indicated that they were part of a normal process of axoneme instability in human sperm.

Adult↗
PubMed1969

Comparison of serological and bacteriological methods in the confirmation of plague infections.

A recent, defined outbreak of bubonic plague in a remote area of the central highlands of Viet-Nam provided an opportunity to undertake studies of antibody production during the course of infections with Pasteurella pestis (Yersinia pestis). The haemagglutination (HA) test of Chen & Meyer, modified to a microtechnique, was used in studies of patients with clinical plague, and in studies of unvaccinated, asymptomatic contacts of plague patients.HA antibody was demonstrated in the sera of nearly 45% of the unvaccinated, asymptomatic contacts of plague patients, and a large proportion of these exhibited 4-fold or greater rises in titre during the outbreak. In 6 of the 16 clinical plague cases, the diagnosis could not be confirmed by bacteriological methods; however, 5 of the 6 exhibited HA antibody in sera collected on admission or in second sera collected 9-14 days later or in both. Of the 5 with positive sera, 4 had very mild clinical illnesses (pestis minor). These findings were in sharp contrast to those among the 8 surviving, bacteriologically confirmed cases, most of whom had clinically very severe illnesses. Only 1 of the 8 had demonstrable plague HA antibody in acute and early convalescent sera; however, all of the latter on whom follow-up studies could be obtained exhibited HA antibody in sera collected 1-1(1/2) months later.These findings indicate that natural active immunization with P. pestis was occurring during the outbreak, and further, that developing immunity from earlier subclinical infections may have accounted for amelioration of clinical signs and symptoms, as well as for failure to isolate P. pestis in patients with pestis minor.HA tests may be particularly useful in confirming the diagnosis of plague if employed with sera collected 3-6 weeks after the onset of illness. The HA test would appear also to provide a highly reliable tool in surveys for plague in areas of unknown endemicity.

Follow-Up Studies↗
PubMedDate not supplied

Dynamic retinoscopy: the missing data.

Dynamic retinoscopy is a well described but often overlooked technique that allows rapid assessment of accommodative ability. The key to the technique is the neutralization of the retinoscopic reflex that occurs when the patient accommodates on a target adjacent to the retinoscope. This clinical tool can provide critical data that can help solve treatment dilemmas, such as when a child presents with high hyperopia or when a patient presents at any age with possible accommodative insufficiency. In this review, performance of dynamic retinoscopy will be detailed, with the applicability of the technique demonstrated with use of case examples.

Accommodation, Ocular↗
PubMedDate not supplied

Vitamin E protects against retinopathy of prematurity through action on spindle cells.

In the premature infant, exposure of the incompletely vascularized retina to increased oxygen tension can result in the development of a blinding disease, retinopathy of prematurity (ROP). Despite the judicious curtailment of oxygen, the incidence of ROP is on the increase due to the technological advances that have improved the survival of the very young preterm infant. Six clinical trials have documented the efficacy of vitamin E supplementation in suppressing the development of severe ROP, but the mechanism of this protection has remained unknown. This report proposes that spindle cells, mesenchymal precursors of the inner retinal capillaries, are the primary inducers of the neovascularization associated with ROP. Exposure of spindle cells to elevated oxygen tension increases their gap junction area. This early morphologic event immediately halts the normal vasoformative process and eventually triggers the neovascularization that is observed clinically 8-12 weeks later. Vitamin E supplementation above the deficient plasma levels of these infants suppresses gap junction formation and clinically reduces the severity without altering the total incidence of ROP.

Humans↗
PubMedDate not supplied

Birefringence-based eye fixation monitor with no moving parts.

For the purpose of vision screening, we develop an eye fixation monitor that detects the fovea by its unique radial orientation of birefringent Henle fibers. Polarized near-infrared light is reflected from the foveal area in a bow-tie pattern of polarization states, similar to the Haidinger brush phenomenon. In contrast to previous devices that used scanning systems, this instrument uses no moving parts. It rather utilizes four spots of linearly polarized light-two aligned with the "bright" arms and two aligned with the "dark" arms-of the bow-tie pattern surrounding the fovea. The light reflected from the fundus is imaged onto a quadrant photodetector, whereby the circular polarization component of the polarization state of each reflected patch of light is measured. The signals from the four photodetectors are amplified, digitized, and analyzed. A normalized differential signal is computed to detect central fixation. The algorithm is tested on a computer model, and the apparatus is tested on human subjects. This work demonstrates the feasibility of a fixation monitor with no moving parts.

Adult↗
PubMedDate not supplied

Automated analysis of electromyographic (EMG) recordings during botulinum injections.

PURPOSE: Botulinum toxin is injected into extraocular muscles using electromyographic (EMG) guidance to confirm needle location prior to injection. The purpose of this study was to develop and test an automated, objective method of storing and grading EMG signal quality obtained during botulinum injection. A reliable, nonsubjective estimate of signal quality will enhance future studies of the complications or effectiveness of botulinum toxin injections into extraocular muscle. METHODS: Injections were administered using a standard procedure. The EMG was digitized, recorded, and analyzed using discrete Fourier transform and power spectrum analysis. Audible signal quality was also graded subjectively by the surgeon. Patients were followed to determine the clinical response to the injection. RESULTS: Eighteen patients (24 injections) were studied. Each sample was collected and analyzed in less than one second. The EMG contained signals over a range of frequencies from 50 to 500 Hz, with an average peak near 90 Hz. Substantial variability of the signal was observed between patients. Contracting muscle had a higher total power and peak frequency in most, but not all, cases. Total signal power correlated moderately with subjective estimates of signal quality. Neither subjective nor computer-derived signal quality estimates correlated with the response to injection or complications. CONCLUSIONS: Computerized signal analysis can automatically characterize EMG signal power and frequency distribution. Although this technique has the potential to identify needle location at the time of botulinum injection accurately, signal variability limited the clinical and research utility of the present protocol.

Botulinum Toxins↗