Search PubMed⌕ Search

Biomedical subjects

A C Bird

Publications and source records attributed to A C Bird.

At least 127 records · Page 7Linked to original sources
PubMed1997

Relationship between napping and melatonin in the blind.

Daytime sleepiness is a common complaint in blind subjects. Abnormally timed melatonin has been invoked as a possible cause of both daytime sleepiness and nighttime awakening. In free-running blind individuals, there is an opportunity to assess the relationship between endogenous melatonin rhythms and subjective sleepiness and naps. The aim of this study was to characterize melatonin rhythms and simultaneously to evaluate subjective napping. A total of 15 subjects with no conscious light perception (NPL) were studied for 1 month. Prior to the study, sleep disorders were assessed using the Pittsburgh Sleep Quality Index. Cosinor and regression analysis revealed that 9 of the 15 NPL subjects had free-running 6-sulphatoxymelatonin (aMT6s) rhythms (period [tau] range = 24.34 to 24.79 h), 3 were entrained with an abnormal phase, and 3 were normally entrained. Most of the subjects (13 of 15) had daytime naps; the 2 individuals who did not made conscious efforts not to do so. Subjects with abnormal aMT6s rhythms had more naps of a longer duration than did those with normal rhythms. Free-running nap rhythms occurred only in subjects with free-running aMT6s rhythms. The 2 abnormally entrained subjects who napped did so at times that coincided with high levels of aMT6s (mean aMT6s acrophase [phi] +/- SD = 14.30 +/- 1.08 h, 20.30 +/- 0.62 h; mean nap time +/- SD = 14.01 +/- 3.60 h, 18.23 +/- 3.20 h, respectively). Regardless of aMT6s rhythm abnormality, significantly more naps occurred with a 4-h period before and after the estimated aMT6s acrophase. In 4 free-running subjects, aMT6s acrophase (phi) passed through an entire 24-h period. When aMT6s was in a normal phase position (24:00 to 06:00 h), night-sleep duration tended to increase with a significant reduction in the number and duration of naps. Sleep onset and offset times tended to advance and delay as the aMT6s rhythms advanced and delayed. Our results show a striking relationship between the timing of daytime production of melatonin and the timing of daytime naps. This suggests that abnormally timed endogenous melatonin may induce sleepiness in blind subjects.

Adult↗
PubMed1997

Relationship between melatonin rhythms and visual loss in the blind.

Melatonin rhythms were assessed in 49 registered blind individuals by measurement of the urinary metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s). Subjects had different causes of visual loss and were classified as having light perception or better (LP; n = 19) or having no perception of light (NPL; n = 30). Subjects collected four-hourly urine samples (eight-hourly overnight) for 48 h at weekly intervals for 3-5 weeks. The majority of LP subjects (14 of 19) had normally entrained aMT6s rhythms (mean acrophase range, 2.4-6.2 h), 4 were abnormally entrained to 24 h (mean acrophase range, 8.9-1.0 h), and 1 was unclassified. Conversely, most NPL subjects had abnormal rhythms (23 of 30), the incidence of which was greater in uni- and bilaterally enucleated subjects. The majority of NPL subjects (17 of 30) had free-running aMT6s rhythms period range, 24.13-24.79 h), 5 were abnormally entrained to 24 h (acrophase range, 7.2-20.6 h), and 1 was unclassified. Output (micrograms of aMT6s per 24 h) and amplitude (micrograms per h) of aMT6s production did not vary between LP and NPL subjects (mean 24-h output +/- SD, 12.7 +/- 7.5 and 9.4 +/- 6.4 micrograms aMT6s/24 h, respectively; mean amplitude +/- SD, 0.6 +/- 0.4 and 0.5 +/- 0.3 microgram/h, respectively). These results indicate that a higher proportion of NPL subjects have abnormal melatonin rhythms compared to those with LP.

Adult↗
PubMed1997

Fundus autofluorescence in age-related macular disease imaged with a laser scanning ophthalmoscope.

PURPOSE: To image and quantify the spatial distribution of fundus autofluorescence in normal subjects, to determine its age dependence, and to document the deviation from normal in patients with age-related macular disease. METHODS: Using a confocal laser scanning ophthalmoscope (cLSO), the intensity and spatial distribution of fundus autofluorescence was studied in 33 normal subjects, 97 eyes with drusen only, and 111 eyes with visual loss caused by age-related macular disease. RESULTS: Fundus autofluorescence intensity in normal subjects was highest at the posterior pole and dipped at the fovea. Autofluorescence increased with age at the posterior pole. Fundus in eyes with age-related maculopathy showed localized high autofluorescence that did not correspond with drusen. Linear pigmentation at the level of the retinal pigment epithelium (RPE), whether detached or flat, fluoresced brightly, whereas plaques of melanin did not. Areas of low and high levels of autofluorescence were seen in lesions containing choroidal new vessels. In areas of geographic atrophy, autofluorescence was low. CONCLUSIONS: The spatial distribution of background fundus autofluorescence and the correlation of autofluorescence with age in normal subjects imply that autofluorescence is derived from lipofuscin at the level of the RPE. Focal accumulation of autofluorescent material occurs at the level of the RPE in patients with drusen, but the drusen do not show marked increases in autofluorescence. It is likely that melanolipofuscin accounts for the high levels of autofluorescence, corresponding to linear pigmentation at the level of the RPE. Low-intensity autofluorescence occurs in the presence of retinal photoreceptor loss, and variable levels over disciform lesions probably relate to variations in metabolic activity of the RPE.

Adolescent↗
PubMed1997

Localization of CSNBX (CSNB4) between the retinitis pigmentosa loci RP2 and RP3 on proximal Xp.

PURPOSE: Proximal Xp harbors many inherited retinal disorders, including retinitis pigmentosa (RP) and congenital stationary night blindness, both of which display genetic heterogeneity. X-linked congenital stationary night blindness (CSNBX) is a nonprogressive disease causing night blindness and reduced visual acuity. Distinct genetic loci have been reported for CSNBX at Xp21.1, which is potentially allelic with the RP3 gene, and at Xp11.23, which is potentially allelic with the RP2 gene. The study to identify the RP2 gene led to an extended study of families with potentially allelic diseases that include CSNBX. METHODS: Haplotype analysis of a family diagnosed with CSNBX was performed with 17 polymorphic markers on proximal Xp covering previously identified loci for CSNBX and XLRP. Two-point and multipoint lod scores were calculated. RESULTS: Informative recombinations in this family define a locus for CSNBX (CSNB4) with flanking markers DXS556 and DXS8080 on Xp11.4 to Xp11.3, an interval spanning approximately 5 to 6 cM. A maximum lod score of 3.2 was calculated for the locus order DXS556-1 cM-(CSNB4-DXS993)-2 cM-DXS1201. CONCLUSIONS: The results describe a new localization for CSNBX (CSNB4) between the RP2 and RP3 loci on proximal Xp. CSNB4 is not allelic with any previously reported XLRP loci; however, the interval overlaps the locus reported to contain the cone dystrophy (COD1) gene, and both diseases are nonrecombinant with DXS993. Because mutations in the RPGR gene to date account for disease in only a small proportion of RP3 families, the possibility that this new locus (CSNB4) also segregates with an as yet unidentified XLRP locus cannot be excluded.

Chromosome Mapping↗
PubMed1996

Partial laser ablation of massive peripapillary subretinal neovascularization.

BACKGROUND: Although peripapillary subretinal neovascular membranes (PSRNs) are less common and often larger than neovascular complexes arising near the fovea, they may lead to severe visual loss. Very large (massive) PSRNs (MPSRNs) are 3.5 disc areas or greater in overall size, are even less common, and may contain a significant occult component, leading to slow and unpredictable growth. Such massive lesions may begin at the nasal margin of the disc and do not become symptomatic until they have extended around the disc toward the macula, threatening central vision. Although complete laser ablation has been used for symptomatic PSRNs with variable success, the optimal treatment of MPSRNs remains controversial. METHODS: The authors reviewed the clinical course of 12 eyes of seven patients with MPSRNs. Ten eyes received laser treatment, which was limited to the temporal portion of the subretinal neovascular complexes only and two received no treatment. RESULTS: Of the ten eyes receiving laser treatment, six showed stabilization of visual acuity, whereas in four the neovascular membrane progressed beneath the fovea with severe visual loss. In the two untreated eyes, the subretinal neovascular membrane progressed beneath the macula with the loss of central vision. CONCLUSIONS: In contrast to the small symptomatic PSRNs, which are usually treated by complete laser ablation, MPSRNs may stabilize with only partial laser treatment. However, both types of lesions may remain stable for long periods of time without any treatment and require treatment only if progression toward the fovea occurs.

Adult↗
PubMed1996

Clinical features of progressive bifocal chorioretinal atrophy: a retinal dystrophy linked to chromosome 6q.

PURPOSE: The gene for progressive bifocal chorioretinal atrophy (PBCRA) has been linked to chromosome 6q, near the genomic assignment for North Carolina macular dystrophy. A study was undertaken to define the clinical features of a large PBCRA pedigree and to determine whether PBCRA and North Carolina macular dystrophy are phenotypically distinct entities. METHODS: Fifteen affected individuals from 1 large family were examined clinically, which included angiography and electrophysiologic studies. RESULTS: The PBCRA is an autosomal dominant chorioretinal dystrophy of early onset characterized by large atrophic macular and nasal retinal lesions, nystagmus, myopia, poor vision, and slow progression. A large atrophic macular lesion and nasal subretinal deposits are evident soon after birth. An atrophic area nasal to the optic nerve head appears in the second decade, which enlarges progressively. Electro-oculographic and electroretinographic studies indicated marked, diffuse abnormalities of rod and cone function. Fluorescein and indocyanine green angiography showed a large circumscribed area of macular choroidal atrophy with staining of deposits in the peripheral retina. In addition to previously documented features, nasal retinal abnormalities from a few weeks of age, marked photopsia in a number of patients, and retinal detachments in three eyes are reported as new features of the disease. CONCLUSIONS: An extended description of PBCRA is presented highlighting that the phenotype is distinct from North Carolina macular dystrophy, although some phenotypic similarities exist between the two conditions. These disorders may be the result of different mutations on the same gene or nearby genes.

Adolescent↗
PubMed1996

Retinopathy in haemoglobin C trait.

Retinopathy associated with sickle-C and sickle cell disease is well described. Sickle trait and haemoglobin C trait are generally considered benign conditions, with infrequent systemic manifestations. Rare cases of retinopathy in sickle trait, in the presence of contributory factors, exist and we recently reported three such patients. The occurrence of retinopathy in haemoglobin C trait is even less well documented. Haemoglobin C does not cause red blood cell sickling but is known to decrease erythrocyte plasticity and increase blood viscosity. We report three cases in which haemoglobin C trait was associated with significant peripheral vascular occlusion and seafan formation (confirmed by fluorescein angiography) similar to that seen in sickle retinopathy. Two patients had coexistent systemic disease (hypertension and diabetes mellitus). Vitreous haemorrhage was the presenting feature in two patients. It is evident that haemoglobin C trait may be associated with sight-threatening complications.

Adult↗
PubMed1996

The gene responsible for autosomal dominant Doyne's honeycomb retinal dystrophy (DHRD) maps to chromosome 2p16.

Degeneration in the macula region of the retina is a feature of a heterogeneous group of inherited, progressive disorders, causing blinding visual impairment. Autosomal dominant Doyne's honeycomb retinal dystrophy (DHRD) is characterised by the presence of drusen deposits at the level of Bruch's membrane in the macula and around the edge of the optic nerve head. We have studied 63 members of a large, nine-generation British pedigree by linkage analysis. Two-point analysis showed significant linkage to nine markers on the short arm of chromosome 2, a region overlapping that recently reported to be linked to Malattia leventinese. A maximum lod score (Zmax) of 7.29 (theta = 0.0) was obtained at marker locus D2S2251. Haplotype analysis of recombination events localised the disease to a 5 cM region between marker loci D2S2316 and D2S378. Striking clinical similarities between DHRD and the more common condition age-related macular degeneration (ARMD) suggest that the disease gene at this locus could be considered as the most likely candidate in future studies on ARMD.

Chromosome Mapping↗
PubMed1996

Sorsby's fundus dystrophy in the British Isles: demonstration of a striking founder effect by microsatellite-generated haplotypes.

Sorsby's fundus dystrophy (SFD) has been mapped to a genetic interval of 8 cM between loci D22S275 and D22S278. A total of 15 families, unrelated on the basis of genealogy and expressing the SFD phenotype were identified from a large data base of genetic eye disease families originating from diverse parts of the British Isles. The identification of the same Ser181Cys mutation cosegregating with disease in each family led us to consider the hypothesis of a founder effect being present. In all families studied, the same relatively infrequent allele (occurring in just 11% of the control group) was associated with disease at marker locus D22S280. A highly significant disease-associated haplotype, spanning across 3 cM of the SFD locus, was conserved in 11 of the 15 families (68% of all affected chromosomes); a further extended haplotype spanning up to 7 cM, was identified in 5 families (27% of SFD-associated chromosomes) and possibly represents the ancestral haplotype. This haplotype analysis has refined the TIMP3 gene localization to a 1- to 3-cM interval between marker loci D22S273 and D22S281 and provides strong evidence for a single mutational event being responsible for the majority of SFD identified in the British Isles.

Alleles↗
PubMed1996

A randomised prospective study of outpatient haemodilution for central retinal vein obstruction.

PURPOSE: Central retinal vein obstruction (CRVO) has significant visual morbidity. We prospectively evaluated an outpatient haemodilution (HD) regimen for CRVO. METHODS: We recruited 59 patients with CRVO of less than three months' duration and visual acuity (VA) worse than or equal to 6/9.5. Thirty patients underwent HD (packed cell volume of <0.35, 12 weeks); there were 29 controls and follow-up was for six months. RESULTS: Incidence rates for VA improvement (P = 0.708) and rubeosis iridis (P = 0.619) between the two groups were not different. The incidence rate of VA deterioration was 5.315 times higher with HD (P = 0.035, Cox Proportional analysis). CONCLUSION: This data does not support the previous studies on haemodilution.

Adult↗
PubMed1996

The venous closing pressure in central retinal vein obstruction.

OBJECTIVE: To assess the rate of change in the central retinal venous closing pressure in central retinal vein obstruction over time, and its relationship to visual acuity improvement and the development of rubeosis iridis. METHODS: Fifty patients presenting with central retinal vein obstruction of less than three months' duration, between the ages of 40 and 80 years, were reviewed prospectively. The central retinal venous closing pressure was measured by digital ocular compression. Patients were discharged from the study after the six-month visit. RESULTS: All patients had elevated venous closing pressure at presentation, whereas at six months only 24 patients had persistent elevation. Of 16 patients with lowering of the venous closing pressure within four months of onset of central retinal vein obstruction, 11 (69%) had two or more lines of visual acuity improvement. Only two of 10 patients (20%) developing lowering of the venous closing pressure thereafter had visual improvement. No patient developed rubeosis iridis after the venous closing pressure lowered. CONCLUSION: The central retinal venous closing pressure is raised in central retinal vein obstruction to about central retinal arterial diastolic pressure, and is its pathognomonic sign. This sign is easily elicited via digital pressure on the eyelid, and has prognostic significance for visual acuity improvement and the development of rubeosis iridis.

Adult↗
PubMed1996

A new family linked to the RP13 locus for autosomal dominant retinitis pigmentosa on distal 17p.

A form of autosomal dominant retinitis pigmentosa (ADRP) mapping to chromosome 17p has been reported in a single large South African family. We now report a new family with severe early onset ADRP which maps to 17p. Linkage and haplotype analysis in this family places the ADRP locus in the 5 cM interval between markers AFMc024za5 and D17S1845, confirming the data obtained in the South African family. The discovery of a second 17p linked family may imply that this is one of the more common loci for dominant RP. In addition, the confirmation of an RP diagnosis at this locus is of interest since loci for a dominant cone dystrophy and Leber's congenital amaurosis (LCA1) have recently been linked to the same markers. While the cone dystrophy locus may be allelic with RP, our data and that of Goliath et al show that distinct genes are responsible for dominant RP and Leber's congenital amaurosis on chromosome 17p.

Chromosomes, Human, Pair 17↗
PubMed1996

Autosomal dominant optic atrophy with asymptomatic peripheral neuropathy.

The association between hereditary motor and sensory neuropathy (HMSN) and optic atrophy has been termed HMSN type VI. The autosomal dominant inheritance of this syndrome is reported. Three generations were affected with optic atrophy, which differed in some respects from classic dominant optic atrophy, and an asymptomatic, mainly sensory, neuropathy.

Adult↗
PubMed1996

Retinal angiography in divers.

OBJECTIVE: In the light of previous reports, to examine the possibility that professional diving might cause abnormalities of the retina and choroid. METHODS: The retinal fluorescein angiograms of 55 Royal Naval divers and 24 non-diver servicemen were compared. RESULTS: No differences were found between divers and non-divers and the prevalence of abnormalities was not correlated with diving experience. CONCLUSION: In contrast to previous reports, there seem, at least in naval personnel, to be no ocular consequences of diving.

Adult↗
PubMed1995

Autosomal dominant macular dystrophy simulating North Carolina macular dystrophy.

OBJECTIVE: To characterize an autosomal dominant macular dystrophy with highly variable expression that does not fall clearly into a known disease entity. METHODS AND PATIENTS: Clinical, angiographic, and electrophysiologic data of five affected members in a family of Indian origin were evaluated. Molecular genetic analysis was undertaken to assess whether the gene responsible for the phenotype in this pedigree mapped to a region previously assigned to dominantly inherited macular dystrophies, including North Carolina macular dystrophy. RESULTS: The fundus appearance in the proband simulated stage 3 North Carolina macular dystrophy. Affected relatives had features in common with pattern dystrophy, fundus flavimaculatus with a dark choroid, and dominantly inherited drusen. Linkage to loci assigned to a number of retinal dystrophies principally affecting the posterior pole, including the North Carolina macular dystrophy locus, was excluded. CONCLUSION: The findings support the view that different genotypes are associated with similar phenotypes in autosomal dominant macular dystrophy.

Adult↗
PubMed1995

Chromosome 19q cone-rod retinal dystrophy. Ocular phenotype.

OBJECTIVE: To describe the phenotype in a family with dominantly inherited cone-rod dystrophy with chromosome assignment to a 19q locus, and to correlate this with current classifications of this retinal dystrophy. DESIGN: A detailed clinical examination including Goldmann perimetry was undertaken in all family members. Six members under the age of 30 years underwent dark-adapted electroretinography, color contrast-sensitivity measurement, dark-adapted static perimetry, and dark adaptometry. PATIENTS: The study included 34 affected and 22 unaffected patients in four generations of a pedigree that manifested autosomal dominant cone-rod retinal dystrophy linked to a chromosome 19q locus by genetic linkage analysis. RESULTS: Loss of visual acuity occurred in the first decade of life, onset of night blindness occurred after 20 years of age, and little visual function remained after the age of 50 years. Central and, later, peripheral retinal fundus changes were associated with central scotoma, pseudoaltitudinal field defects, and finally global loss of function. Psychophysical and electrophysiologic testing before the age of 26 years showed more marked loss of cone than rod function. CONCLUSIONS: The phenotype associated with this mutation does not fit well into previous subtypes of cone-rod dystrophy. Further studies will be needed to correlate specific genetic mutations in this group of conditions with the various clinical phenotypes.

Adolescent↗