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Biomedical subjects

D G Hunter

Publications and source records attributed to D G Hunter.

At least 19 recordsLinked to original sources
PubMed2001

Redefining papillorenal syndrome: an underdiagnosed cause of ocular and renal morbidity.

PURPOSE: To report ocular and renal findings specific to the inheritable entity called papillorenal (also known as renal-coloboma) syndrome and relate these to a common cause. DESIGN: Observational case series and genetic study. PARTICIPANTS: Two unrelated probands presenting with absent central retinal vessels and 11 available family members. TESTING: Doppler ultrasonographic imaging of the optic nerves and kidneys, fluorescein angiography, and genetic testing for PAX2 mutations were performed. In selected cases, indocyanine green angiography, scanning laser ophthalmoscope perimetry, Retinal Thickness Analyzer measurements, visual evoked potentials, and magnetic resonance imaging were also performed. MAIN OUTCOME MEASURES: Better defined characteristics of the papillorenal syndrome. RESULTS: Numerous cilioretinal vessels were present with rudimentary or absent central retinal vessels. Superonasal visual field defects, typical for papillorenal syndrome, corresponded to inferotemporal areas of anomalous retinal and choroidal perfusion and hypoplastic retina. Renal hypoplasia was discovered in two affected members of one family (with previously unsuspected renal failure in one case), and recurrent pyelonephritis was discovered in four affected members of the other family. No PAX2 mutations were detected. CONCLUSIONS: In the papillorenal syndrome, the hereditary absence of central retinal vessels may be missed, leading to confusion with isolated coloboma, low-tension glaucoma, and morning glory anomaly. Greater awareness of this syndrome will avoid unneeded glaucoma therapy, allow earlier recognition of renal diseases, and allow genetic counseling. We propose that the papillorenal syndrome is a primary dysgenesis that causes vascular abnormalities predominantly affecting the eye, kidney, and urinary tract, leading to hypoplasia of these structures. The absence of defects in the PAX2 gene in these families suggests that mutations in other genes may also be responsible for this syndrome.

Adult↗
PubMed2001

An adjustable superior oblique tendon spacer with the use of nonabsorbable suture.

PURPOSE: Philip Knapp described a method, sometimes referred to as the "chicken suture,"of securing a loose nonabsorbable suture to the cut ends of the superior oblique tendon to facilitate future reversal. The purpose of this study is to describe a modification of Knapp's technique to achieve partial, reversible, and intraoperatively adjustable superior oblique weakening. METHODS: The superior oblique tendon was exposed, 2 polyester nonabsorbable sutures were placed 4 mm apart, and the tendon was cut. With the use of a slip knot, the cut ends of the tendon were separated by 2 to 8 mm. Tendon separation was adjusted intraoperatively according to the exaggerated traction test and, in some cases, fundus torsion. Medical records of all patients who underwent surgery with this technique were reviewed and the outcomes tabulated. RESULTS: Twelve patients (16 eyes) were treated for superior oblique overaction and 3 patients (3 eyes) for Brown syndrome. Follow-up was 2 to 46 months (mean, 17 months). Mean superior oblique overaction improved from +1.3 before surgery to +0.3 after surgery, mean A pattern improved from 20 PD to 2 PD, and fundus intorsion improved from +1.2 to +0.3. In Brown syndrome, the mean elevation in adduction improved from -3.8 to -1.0. One patient from each group developed an overcorrection. None of the patients developed recurrence. The patients with Brown syndrome continued to improve over a 1-year period. CONCLUSIONS: The superior oblique tendon suture spacer is effective, intraoperatively adjustable, and technically easier to perform than a silicone expander procedure. This technique should be considered as an alternative for patients requiring superior oblique weakening.

Adolescent↗
PubMed2001

Superior oblique overaction from local anesthesia for cataract surgery.

Traumatic superior oblique dysfunction from cataract surgery appears to be rare, with only 3 reported cases of postoperative Brown syndrome and 1 reported case of postoperative superior oblique weakness. We are not aware of any prior reports of superior oblique overaction occurring after cataract surgery. We describe a patient with acquired superior oblique overaction as a cause of vertical strabismus after cataract surgery. Ocular torsion analysis was essential in localizing the malfunction to the superior oblique muscle. The most likely etiology is myotoxicity from inadvertent intramuscular injection of local anesthetic before cataract surgery.

Anesthesia, Local↗
PubMed2001

Diplopia after limited macular translocation surgery.

PURPOSE: Full macular translocation surgery relocates the fovea away from choroidal neovascularization, inducing significant postoperative torsional diplopia. In "limited macular translocation," a saline-induced retinal detachment is followed by scleral imbrication with mattress sutures and spontaneous retinal reattachment. In this study, diplopia was characterized in patients treated with limited macular translocation. METHODS: Two surgeons performed retinal translocation surgery on 250 patients over an 18-month time span. The extent and direction of the retinal translocation, and the amount and location of scleral imbrication, were recorded. All patients complaining of diplopia were referred for ocular motility evaluation and treatment. RESULTS: Thirteen (5.2%) patients complained of occasional or constant diplopia. Imbricating sutures were placed supero-temporally in all cases. Inferior foveal translocation ranged from 200 to 2115 microm (median, 1750 microm). Visual acuity ranged from 20/40 to 20/400 in the operated eye. Prism-and-cover testing underestimated the strabismus when compared with subjective testing. In 3 patients, there was no shift on alternate-cover testing despite binocular diplopia. Excyclotorsion ranged from 0 degrees to 16 degrees. Diplopia resolved in 10 cases with prism; 3 required an occlusive filter for distortion or aniseikonia. One patient underwent successful strabismus surgery to eliminate dependence on prism glasses. CONCLUSIONS: Limited macular translocation only rarely produces symptomatic diplopia. Suprisingly, traditional prism-and-cover testing does not reliably quantify the misalignment. This may result from the combination of a persistent macular scotoma and a repositioned fovea relative to the peripheral retina. Prism therapy is generally satisfactory in the absence of retinal distortion or aniseikonia.

Aged↗
PubMed2001

Long-term outcome of uncomplicated infantile exotropia.

PURPOSE: The term congenital exotropia (XT) is typically reserved for patients presenting in the first year with a large, constant angle, however, no published study provides a rationale for this restrictive definition. In this study, the present classification system for XT was evaluated and differences between infants with constant versus intermittent XT at presentation were characterized. METHODS: Medical records of all patients diagnosed with XT before 12 months of age between 1980 and 1994 were identified by computer search. Exclusion criteria included previous eye muscle surgery, resolution of the XT by 3 months of age, and concomitant systemic or ocular disease. Patients were separated into intermittent XT and constant XT groups. The clinical characteristics and outcomes of these two groups were compared. RESULTS: Of 2018 patients examined on our service during the first year of life for all causes, 23 (1.1 %) met the inclusion criteria. Follow-up data of more than 1 year was available for 13 patients, and of these, 46% had constant XT. The 2 groups had similar clinical features at presentation except for a larger initial angle in the constant XT group (P =.02). Average follow-up was 58 months (range: 13-158 months). Twelve patients (92%) required surgery. The reoperation rate was 27%, and 82% had final horizontal deviations of less than 10 PD. The incidence of A/V-patterns (38%), dissociated vertical deviation (46%), and binocularity (70%) was similar between groups. CONCLUSION: Half of infantile XT patients may present with intermittent XT, with similar clinical outcomes regardless of presentation. Surgical intervention resulted in successful alignment in most cases. More than half the patients developed measurable stereopsis, but none achieved bifixation.

Depth Perception↗
PubMed2000

Investigation into the relationship between the passive flexibility and active stiffness of the ankle plantar-flexor muscles.

OBJECTIVE: The purpose of the study was to investigate the relationship between measurements of passive flexibility and active stiffness of the ankle plantar-flexor muscles. DESIGN: The study was a correlation design. BACKGROUND: Flexibility has passive and active components. Little information is available regarding the relationship of these measurements in terms of the information that they yield on the state of the muscle-tendon unit. METHODS: Free oscillation data representing active stiffness was obtained using applied masses equivalent to 30%, 60% and 90% of the subject's maximal voluntary contraction. The angle of dorsiflexion, representing passive flexibility, was measured in standing using computer digitisation to obtain the angle.Results. Mean active stiffness values were 14280 N/m (30% maximal voluntary contraction), 22260 N/m (60% maximal voluntary contraction) and 28010 N/m (90% maximal voluntary contraction). Dorsiflexion measurement gave a mean of 34.3 degrees (S.D. 4.8). Correlation's obtained for the association between range of motion and active stiffness were r=0.01 (30% maximal voluntary contraction), r=0.09 (60% maximal voluntary contraction) and r=0.04 (90% maximal voluntary contraction). Moderate reliability coefficients of 0.71 (30% maximal voluntary contraction), 0.78 (60% maximal voluntary contraction) and 0.68 (90% maximal voluntary contraction) were obtained. CONCLUSIONS: The results imply that measurements of passive flexibility and active stiffness of the lower leg musculature are independent measures of components of muscle-tendon unit flexibility. RELEVANCE: Flexibility is a construct with different components of measurement. Etiological studies typically relate static flexibility measurements to injury with conflicting outcomes. This study suggests that static and active flexibility measures yield different information about the muscle tendon unit of the ankle plantar flexors, and that researchers should consider this point in the design of etiological studies.

Adult↗
PubMed1999

Endogenous retroviruses provide the primary polyadenylation signal for two new human genes (HHLA2 and HHLA3).

By screening the expressed sequence tag (EST) database, we identified transcripts of two new human genes that are polyadenylated within a long terminal repeat (LTR) of the HERV-H endogenous retrovirus family. The first gene, termed HHLA2, is represented by two EST clones and one cDNA clone, all of which have a polyadenylated LTR as their 3' end. The gene has an open reading frame (ORF) of 414 amino acids with three immunoglobulin-like domains and is expressed primarily in intestinal tissues, kidney, and lung. Seven small EST clones from several different tissues were found for the second gene, termed HHLA3. As with HHLA2, all HHLA3 ESTs utilized a HERV-H LTR as the polyadenylation signal. Three types of alternatively spliced HHLA3 transcripts that could encode proteins of 76, 121, or 153 amino acids were detected. Interestingly, the ORF for two of these transcripts continues into the LTR. For both HHLA2 and 3, no major human transcripts that utilized a non-LTR polyadenylation signal were detected. Analysis of RNA from baboon, which lacks the LTRs at these genomic loci, showed that the baboon HHLA2 and 3 genes use other polyadenylation signals. This study demonstrates that ancient retroviral insertions have assumed gene regulatory functions during the course of human evolution.

Amino Acid Sequence↗
PubMed1999

Prevalence of systemic and ocular disease in infantile exotropia: comparison with infantile esotropia.

OBJECTIVE: Exotropia in infancy is believed to be associated with an increased prevalence of neurologic, ocular, and craniofacial abnormalities; however, the prevalence of coexisting ocular and systemic disease in these patients is unknown. In this study, the prevalence of ocular disease and systemic illness was determined in patients diagnosed with exotropia in infancy. DESIGN: Observational comparative case series. PARTICIPANTS: Medical records of 70 patients diagnosed with exotropia in the first year of life were reviewed and compared with records of 136 patients diagnosed with esotropia before 1 year of age. INTERVENTION: Patients with no disorders (other than latent nystagmus, dissociated vertical deviation, or oblique muscle overaction) were grouped as "simple" strabismus. Patients with systemic disorders (including prematurity, neurologic disease, and genetic disease) and patients with ocular disorders (including congenital nystagmus, other strabismus, ptosis, and any condition associated with loss of vision [except amblyopia]) were grouped as "complex" strabismus. MAIN OUTCOME MEASURES: Prevalence of coexisting systemic and ocular disorders. The demographics, strabismus measurements, and types of coexisting disease in the simple and complex groups were compared. RESULTS: A high percentage of both exotropia (67%) and esotropia (49%) patients had a coexisting ocular or systemic abnormality. Exotropia patients with a constant strabismus were more likely to have coexisting ocular or systemic disease than those with an intermittent strabismus. Smaller angles of exotropia or esotropia were associated with a higher likelihood of coexisting ocular or systemic diseases. Systemic disorders were found more frequently than ocular disorders in both the exotropia and esotropia groups. In 25% of all patients referred for evaluation of strabismus, an additional ocular or systemic abnormality was discovered by the ophthalmologist. CONCLUSION: Patients presenting to a university hospital-based practice in the first year of life with exotropia were more likely than those presenting with esotropia to have coexisting ocular and systemic disease. Both groups had a notably high prevalence of associated disorders. The percentages measured in this population may not be applicable to other practices because of referral bias. However, clinicians should consider that children presenting with infantile exotropia and esotropia appear to be at risk for coexisting ocular or systemic disease.

Baltimore↗
PubMed1999

A proposed simple method for measurement in the anterior chamber angle: biometric gonioscopy.

OBJECTIVE: To design a system of gonioscopy that will allow greater interobserver reliability and more clearly defined screening cutoffs for angle closure than current systems while being simple to teach and technologically appropriate for use in rural Asia, where the prevalence of angle-closure glaucoma is highest. DESIGN: Clinic-based validation and interobserver reliability trial. PARTICIPANTS: Study 1: 21 patients 18 years of age and older recruited from a university-based specialty glaucoma clinic; study 2: 32 patients 18 years of age and older recruited from the same clinic. INTERVENTION: In study 1, all participants underwent conventional gonioscopy by an experienced observer (GLS) using the Spaeth system and in the same eye also underwent Scheimpflug photography, ultrasonographic measurement of anterior chamber depth and axial length, automatic refraction, and biometric gonioscopy with measurement of the distance from iris insertion to Schwalbe's line using a reticule based in the slit-lamp ocular. In study 2, all participants underwent both conventional gonioscopy and biometric gonioscopy by an experienced gonioscopist (NGC) and a medical student with no previous training in gonioscopy (JK). MAIN OUTCOME MEASURES: Study 1: The association between biometric gonioscopy and conventional gonioscopy, Scheimpflug photography, and other factors known to correlate with the configuration of the angle. Study 2: Interobserver agreement using biometric gonioscopy compared to that obtained with conventional gonioscopy. RESULTS: In study 1, there was an independent, monotonic, statistically significant relationship between biometric gonioscopy and both Spaeth angle (P = 0.001, t test) and Spaeth insertion (P = 0.008, t test) grades. Biometric gonioscopy correctly identified six of six patients with occludable angles according to Spaeth criteria. Biometric gonioscopic grade was also significantly associated with the anterior chamber angle as measured by Scheimpflug photography (P = 0.005, t test). In study 2, the intraclass correlation coefficient between graders for biometric gonioscopy (0.97) was higher than for Spaeth angle grade (0.72) or Spaeth insertion grade (0.84). CONCLUSION: Biometric gonioscopy correlates well with other measures of the anterior chamber angle, shows a higher degree of interobserver reliability than conventional gonioscopy, and can readily be learned by an inexperienced observer.

Adult↗
PubMed1999

An example of intron junctional sliding in the gene families encoding squalene monooxygenase homologues in Arabidopsis thaliana and Brassica napus.

Sequences of three Arabidopsis thaliana and two Brassica napus cDNAs encoding squalene monooxygenase homologues (Sqp1 and Sqp2) are reported. Southern analysis confirmed that these cDNAs are derived from small gene families in both species. Expression analysis indicates that Sqp1 genes in B. napus are strongly expressed in leaves but not roots or developing seeds. Comparison of cDNA and genomic sequences indicate that the 3' splice site of an intron in these genes has undergone junctional sliding. The evolutionary significance of this phenomenon is discussed.

Amino Acid Sequence↗
PubMed1999

Mathematical modeling of retinal birefringence scanning.

Retinal birefringence scanning (RBS) is a new technique that is used to detect the fixation of the eye remotely and noninvasively. The method is based on analysis of polarization changes induced by the retina. In this study, the principles of RBS were mathematically modeled to facilitate a better understanding of the origins of the signals obtained. Stokes vector analysis and Mueller matrix multiplication were augmented with Poincaré sphere representation. The cornea was modeled as a linear retarder. The foveal area was modeled as a radially symmetric birefringent medium. The model accurately predicted the frequency and phase of RBS signals obtained during central and paracentral fixation. The signal that indicates central fixation during RBS likely results from a combination of the radial birefringence of the Henle fibers and the overlying corneal birefringence.

Birefringence↗
PubMed1999

A randomized comparison study of drop versus spray topical cycloplegic application.

PURPOSE: To evaluate the acceptance of ocular spray administration. METHODS: A randomized, single-masked comparison in a cohort of children from 3 to 13 years. Assessment of patient pain was recorded on a visual analog scale. Cycloplegia was assessed by an ophthalmologist masked to the assignment. A questionnaire was used to assess patient acceptance. 126 patients participated. The average age was 7.7 years for spray, 7.1 for drops. RESULTS: Pain (higher number = more painful): means: 41/100 for spray; 35/100 for drops (P=0.28). No difference in cycloplegia noted (i.e., satisfactory in all subjects). Subjective acceptance: high in both patient groups, but a preference for spray was noted (P=0.06). No untoward drug reactions occurred with either method. CONCLUSIONS: Cycloplegic spray was as acceptable, or more acceptable than drops. Cycloplegia was comparable for the two methods. Spray application of cycloplegic drugs is a satisfactory route of topical administration for children.

Administration, Topical↗
PubMed1998

Vertical location of the corneal light reflex in strabismus photography.

OBJECTIVE: To improve the clinical documentation of strabismus by mathematically predicting and clinically verifying the location of a fixation target that produces a vertically centered corneal light reflex (first Purkinje image) in clinical photographs of the eye using a standard photographic flash unit. MATERIALS AND METHODS: Mathematical modeling of the corneal light reflex during clinical photography was based on the schematic eye. Clinical photographs were taken using a range of fixation targets located between the center of the camera lens and the center of the flash. Image quality was also assessed subjectively. RESULTS: Optimum vertical centration of the corneal light reflex was predicted and produced when the fixation target was located one fifth of the distance from the center of the flash to the center of the camera lens. Placement of the flash below, rather than above, the camera lens provided more uniform illumination of the patient's eyes and face. Decreasing the distance between the camera lens and the flash minimized the severity of these artifacts. CONCLUSIONS: A poorly positioned corneal light reflex makes it difficult to identify the fixing eye in photographs of patients with strabismus, especially when vertical strabismus is present. Adoption of the aforementioned protocol will reproduce the appearance of coaxially viewed corneal light reflexes and provide much-needed standardization for strabismus case presentation.

Blinking↗
PubMed1998

Effect of extrusion pressure and lipid properties on the size and polydispersity of lipid vesicles.

The production of vesicles, spherical shells formed from lipid bilayers, is an important aspect of their recent application to drug delivery technologies. One popular production method involves pushing a lipid suspension through cylindrical pores in polycarbonate membranes. However, the actual mechanism by which the polydisperse, multilamellar lipid suspension breaks up into a relatively monodisperse population of vesicles is not well understood. To learn about factors influencing this process, we have characterized vesicles produced under different extrusion parameters and from different lipids. We find that extruded vesicles are only produced above a certain threshold extrusion pressure and have sizes that depend on the extrusion pressure. The minimum pressure appears to be associated with the lysis tension of the lipid bilayer rather than any bending modulus of the system. The flow rate of equal concentration lipid solutions through the pores, after being corrected for the viscosity of water, is independent of lipid properties.

Biophysics↗