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Biomedical subjects

L E Leguire

Publications and source records attributed to L E Leguire.

At least 19 recordsLinked to original sources
PubMed1995

Flash visual evoked response binocular summation in normal subjects and in patients with early-onset esotropia before and after surgery.

Flash visual evoked responses were recorded and visual evoked response binocular summation was assessed in normal children between the ages of 1 and 58 months, in normal adults and in children with early-onset esotropia before and longitudinally for 1 year after surgical binocular alignment. Normal flash visual evoked response binocular summation started in the range of facilitation (> 2.0) at 1 month of age and decreased to adult levels by 3.7 months of age. The shape of the flash visual evoked response binocular summation function obtained from the patients with early-onset esotropia, appeared similar to that of normal subjects; however, the rapid decrease in flash visual evoked response binocular summation from facilitation to normal adult levels occurred after surgical binocular alignment. In normal adults, flash visual evoked response binocular summation was significantly reduced by a 40-diopter base-in prism, suggesting that binocular misalignment was not the reason for the facilitation in flash visual evoked response binocular summation in either childhood population. It is proposed that this facilitation may reflect a process that leads to binocularity and that develops rapidly with binocular alignment.

Adolescent↗
PubMed1993

Fundus pigmentation and the electroretinographic luminance-response function.

Dark-adapted and light-adapted electroretinographic luminance-response functions were recorded from subjects with light or dark fundus pigmentation based on digitized fundus photographs. For dark- and light-adapted electroretinograms, subjects with dark fundi had smaller b-wave amplitudes at all luminance levels. There was no significant difference in b-wave implicit time for the dark-adapted electroretinogram, but there was a significant difference for the light-adapted ERG between the two groups. The results suggest that fundus pigmentation should be considered in the interpretation of electroretinogram results. A possible mechanism for the influence of fundus pigmentation on b-wave amplitude is based on increased resistance associated with melanin.

Adult↗
PubMed1993

Persistently altered T cell immunity in high school students with the congenital rubella syndrome and profound hearing loss.

Because there are frequent progressive and autoimmune complications in children born with the congenital rubella syndrome, we evaluated immunoregulation in eight profoundly deaf adolescents with congenital rubella syndrome who lived in a state school. Serum antiviral antibodies, expressions of peripheral lymphocyte epitopes and serum soluble interleukin 2 receptor (IL-2R) content were compared with those of 16 classmates with profound hearing loss of unknown cause and of 24 age-matched, hearing students from this area. Both deaf groups showed activated but impaired T lymphocyte function compared with normals. Rubella virus alteration of T cell function was suggested in congenital rubella syndrome students by elevated numbers of both CD4+ helper and CD25+ IL-2R cells with unusually low released soluble IL-2R content. In contrast in deaf classmates elevated CD25+ and CD16+ natural killer cell groups and soluble IL-2R content with low numbers of CD4+ helper cells and CD4+ populations were of unknown etiology. Defective immunoregulation of the congenitally deaf to pathogens inherent in their environment may lead to autoimmune and other complications.

Adolescent↗
PubMed1993

Effect of light filters on contrast sensitivity function in normal and retinal degeneration subjects.

Contrast sensitivity functions were measured with five light filters and without a filter, in the presence of a glare source, in 12 retinal degeneration subjects and 9 normal subjects. The light filters included yellow-tinted, CPF 527, NoIR 111, 0.6 neutral density and sunglasses with a 95% UV filter. Retinal degeneration subjects showed a mild improvement in contrast sensitivity at the higher spatial frequencies and maintained mean log contrast sensitivity with light filters which reduced photopic light transmission up to 75%. Normal subjects exhibited a systematic decrease of contrast sensitivity at higher spatial frequencies with all light filters and overall mean log contrast sensitivity was significantly correlated (r = 0.86, P < 0.025) with photopic light transmission of the filters. It is concluded that, when in the presence of a glare source, the benefits of certain light filters to retinal degeneration subjects is related to the reduction of overall photopic luminance.

Adolescent↗
PubMed1993

Levodopa/carbidopa for childhood amblyopia.

PURPOSE: To evaluate the efficacy and tolerance of two low doses of levodopa/carbidopa (25/6.25 mg, 50/12.5 mg) and placebo (Tums) in 20 children with amblyopia between the ages of 4 and 14 years. METHODS: A double-masked placebo-controlled randomized 8-hour study was performed during which subjects received one of two doses of levodopa/carbidopa or placebo, combined with occlusion of the dominant eye. Visual acuity was measured at baseline and at 1 and 5 hours after capsule ingestion. Tolerance was assessed by questionnaire and physical examination. RESULTS: Visual acuity significantly improved by one line, from an overall average of 20/121 to 20/96, in the amblyopic eyes of both groups that received levodopa/carbidopa. Visual acuity did not significantly change in the placebo group. Tolerance was similar among all three groups. CONCLUSION: Average dose levels of 0.95/0.24 mg/kg and 1.94/0.49 mg/kg of levodopa/carbidopa were found to be well tolerated and efficacious at temporarily improving visual acuity in amblyopic eyes of children.

Adolescent↗
PubMed1992

The photopic hill: a new phenomenon of the light adapted electroretinogram.

Utilizing a high intensity photographic flash unit, electroretinograms were recorded from normal adults under fully light adapted conditions over a 5 log unit range of stimulus luminance (-1.35 to 3.34 log cd-s/m2). At lower luminance levels b-wave amplitude increased with increased luminance until it reached a maximum (Vmax of the Naka-Ruston equation) in agreement with previous work. At higher luminance levels, the b-wave amplitude decreased to 33% of Vmax and then plateaued. This previously unreported phenomenon has been named the photopic hill. There was no appreciable change in b-wave amplitude with increased interstimulus intervals from 15 sec to 5 min and luminance-response functions serially recorded for increasing and for decreasing stimulus luminance were very similar. These latter results indicate that the photopic hill is not due to light adaptation. The reason for the photopic hill and possible clinical implications are discussed.

Adaptation, Ocular↗
PubMed1992

Fundus pigmentation and the dark-adapted electroretinogram.

Dark-adapted electroretinograms were obtained over a 3.6-log range of stimulus intensities from 17 black and 15 white normal subjects. Subjects were grouped on the basis of light or dark fundus pigmentation, determined from digitized fundus photographs. B-wave amplitudes for each group were fitted by the Naka-Rushton equation, and the measures Vmax, log K, and n were determined. The luminance-response functions revealed that subjects with light fundi had larger b-wave amplitudes at all luminance levels. There was a significant difference between groups for Vmax and n but not for log K. A comparison of b-wave implicit times showed no significant difference between subjects with dark and light fundi. Ancillary tests and multiple regression analysis suggested that the relationship between Vmax and fundus pigmentation could not be attributed to age, gender, refractive error, axial length or intraocular pressure. The results have implications for the collection of normative electroretinographic data and for the interpretation of electroretinogram results.

Adolescent↗
PubMed1992

Systemic immunostimulation after retinal laser treatment in retinitis pigmentosa.

Systemic immunostimulation followed an experimental treatment trial of scatter argon laser photocoagulation directed to the retina of one eye of 10 patients with heredo-degenerative retinitis pigmentosa (RP). Significantly increased RP lymphocyte CD25, CD26, and CD4/CD26 activation epitope expressions over prelaser values and controls were found with a normalization of soluble interleukin-2 receptor secretion after laser treatment. Serum interferon-gamma was low both pre- and postlaser. Interestingly, when a panel of viral antibodies was tested, only those to rubella virus were elevated in the early postlaser period. The character of RP immunostimulation after laser-induced inflammation could be consistent with an antigenic stimulus from laser-released retinal proteins which might be of autoimmune or latent infectious origin. Enhanced immune responses may be a common but unrecognized sequellae of retinal laser.

Adolescent↗
PubMed1992

Electro-oculogram in vitamin A deficiency associated with cystic fibrosis. Short communication.

Electro-oculograms (EOGs) were recorded in a patient with cystic fibrosis and vitamin A deficiency before and during vitamin A supplementation (25,000 IU/day). Before vitamin A supplementation the EOG Arden light/dark ratio was 1.27. After seven months of vitamin A supplementation the Arden ratio increased to 3.0. These results reveal that vitamin A deficiency can cause an abnormal EOG.

Adolescent↗
PubMed1992

A prospective study of ocular abnormalities in hearing impaired and deaf students.

In a prospective study of 505 hearing impaired and deaf students conducted at Children's Hospital Eye Clinic, 48.7% were found to have significant ocular abnormalities. The prevalence of myopia, astigmatism, and pathological intraocular changes was found to be significantly increased over the general population. In addition, the prevalence of ocular abnormalities generally increased with the severity of the hearing loss. Of importance was the high prevalence of rubella-consistent abnormalities in the hearing impaired and deaf student populations. Rubella syndrome may be responsible for a major portion of high refractive errors and ocular pathological changes. It is recommended that ENT specialists and pediatricians be aware of the nearly 50% chance of ocular abnormality in hearing impaired and deaf students, and that ophthalmologic examination may be valuable for identification or confirmation of the etiology of hearing impairment.

Adolescent↗
PubMed1992

Antibody response to rubella virus antigen and structural proteins in retinitis pigmentosa.

Elevated serum ELISA IgG antibodies to rubella virus (RV) were found by three independent determinations in 41 (72%) of 57 adults with the retinal degeneration retinitis pigmentosa, while antibody responses to five other common neurotropic viruses were normal. However, these patients lacked clinical signs of active RV infection or known recent RV exposure, and 56 lacked IgM anti-RV antibody. Unusual relative percentages of IgG antibody to RV structural proteins compared with those of controls were found in patients' sera by radioimmunoprecipitation assay. For retinitis pigmentosa patients, percentage of RV envelope glycoprotein E1 antibody was similar to, of RV envelope glycoprotein E2 antibody was greater than, and of antibody to RV nucleocapsid C protein was lower than control percentages. Abnormal immunity to RV was also suggested by a lack of increased proliferation of lymphocytes to RV antigen despite elevated anti-RV antibody in patients with retinitis pigmentosa. Not associated with age or particular genetic pattern, these divergences from normal immunity suggest an unusual association between RV proteins and retinitis pigmentosa.

Adolescent↗
PubMed1991

Loss of contrast sensitivity in cystic fibrosis.

We measured the contrast sensitivity function in a 16-year-old boy with cystic fibrosis, before and during vitamin A supplementation. Before vitamin A supplementation, serum levels of vitamin A were abnormally low, the electroretinogram was reduced, and contrast sensitivity was abnormally low at all spatial frequencies. During vitamin A supplementation (25,000 IU/day), serum levels of vitamin A became low normal, the electroretinogram returned to normal, and the overall contrast sensitivity function improved by 94%. We propose that the contrast sensitivity function may be abnormal in patients with cystic fibrosis who have reduced retinal function secondary to vitamin A deficiency.

Adolescent↗
PubMed1991

Dark-adapted luminance-response functions with skin and corneal electrodes.

Normative dark-adapted electroretinograms were recorded simultaneously with a skin electrode and corneal electrode for varying stimulus intensities. The electroretinogram b-wave amplitudes for each electrode were fitted by the Naka-Rushton equation, and the parameters Vmax, K and n were evaluated. A comparison of parameters between the two electrodes showed a significant difference for Vmax and K but not for n. Vmax was approximately eight times smaller and K was 0.3 log unit smaller for the skin electrode than for the corneal electrode. B-wave amplitude and implicit time were also compared between the two electrodes. The b-wave amplitude ratio of the corneal electrode to that of the skin electrode increased with luminance and ranged from 1.83 to 7.68. Overall, b-wave implicit time for the skin electrode was approximately 10 ms shorter than that of the corneal electrode.

Adult↗
PubMed1991

Contrast sensitivity of optokinetic nystagmus.

To determine the threshold characteristics of optokinetic nystagmus (OKN), contrast thresholds for involuntary OKN were measured for gratings of different spatial frequency to yield an OKN-contrast sensitivity function (OKN-CSF). The OKN-CSF resembled an inverted U-shaped function with temporal-to-nasal and nasal-to-temporal movement yielding similar functions. In addition, when psychophysical CSFs were determined for separate form and movement thresholds, it was discovered that the OKN-CSF approximated the psychophysical-movement CSF rather than the psychophysical-form CSF.

Adult↗
PubMed1991

CSF interocular interactions in childhood ambylopia.

Contrast sensitivity functions (CSF's) were measured in the amblyopic and dominant eyes of 17 strabismic and 28 anisometropic children and in 19 similar age normal controls. A three-alternative forced-choice procedure was used to measure CSF's with the VCTS 6500. The results revealed reduced contrast sensitivity (CS) in both the amblyopic and dominant eyes of strabismic and anisometropic amblyopes compared to normal controls. Statistically significant intereye correlations of CS at each spatial frequency were found in all groups and in the presence of deep amblyopia, suggesting continued interocular interactions and binocularity. A separate longitudinal study of 7 of the amblyopes showed that, during the course of occlusion therapy, both the amblyopic and the dominant eyes improved in CSF. The results suggest that the amblyopic eye may influence CS in the dominant eye through interocular interactions. This process may serve to minimize CSF differences between the eyes and maximize binocular vision.

Amblyopia↗
PubMed1991

Visual-evoked response binocular summation in normal and strabismic infants. Defining the critical period.

Pattern visual-evoked response binocular summation (VERBS) was recorded in normal infants, between the ages of 1-58 months, and in similar-aged esotropic infants before and at various times after corrective surgery. The normal subjects had no significant VERBS at 1.5 months of age, developed a rapid acceleration of VERBS between 1.5-3 months, and then gradually declined in VERBS from 3-58 months. The peak of the VERBS by age function at 3 months was well in the facilitation range (greater than 2.0) and corresponded to the general age range for the onset of binocular eye alignment, fusion, and stereopsis. The results from the early-onset esotropic patients revealed a similar function to that found in normal subjects; however, the function was triggered by surgical eye alignment. The peak of the VERBS function for esotropic subjects was lower than normal, and the initial rise was less rapid. It is proposed that the VERBS function reflects the human critical period for the development of binocular vision. In this framework, data from both infant developmental studies and adult studies were clarified.

Adolescent↗
PubMed1990

Architecture and design of a computerised stereogram generator for vision test.

A new microcomputer-based stereogram generator was designed and implemented to generate various visual stimuli that are used for testing the binocular vision system. The system is capable of generating static and dynamic stereoscopic stereograms that can be varied in size, shape, speed and disparity. It can also be used to generate a luminous stimulus on a dark background which, except for the depth parameters, can be varied in a similar way to the stereoscopic stimulus. A 16/32-bit microprocessor has been employed for the overall control of the stereogram parameters, which provides flexibility, versatility, compactness and speed at reduced cost. We have applied this system to the measurement of eye movement and computer vision.

Diagnosis, Computer-Assisted↗