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Biomedical subjects

A C Bird

Publications and source records attributed to A C Bird.

At least 199 records · Page 11Linked to original sources
PubMed1992

Abnormal dark adaptation kinetics in autosomal dominant sector retinitis pigmentosa due to rod opsin mutation.

The time course of dark adaptation was measured in 10 subjects from three families with autosomal dominant sector retinitis pigmentosa (RP) due to mutations in the first exon of the rod opsin gene. In each subject cone adaptation and the early part of the recovery of rod sensitivity followed the normal time course, but the later phase of rod adaptation was markedly prolonged. The recovery of rod sensitivity is much slower than that reported in any other outer retinal dystrophy. Using a model based upon primate data of rod outer segment length and turnover, we have calculated that the delayed phase of the recovery of rod sensitivity in the RP patients tested following strong light adaptation could be due in part to formation of new disc membrane with its normal concentration of rhodopsin rather than in situ regeneration of photopigment.

Adolescent↗
PubMed1992

Confocal imaging of the fundus using a scanning laser ophthalmoscope.

A confocal scanning laser ophthalmoscope (cSLO) was used to examine the effects of confocal optics on the image of the human fundus in vivo. Patients from a retinal clinic and a glaucoma clinic were examined using the cSLO in the confocal mode. A degree of optical sectioning could be achieved, and the results agree with a best axial resolution of 300 microns measured in a model eye. The main advantage of using a confocal system was found to be the improved contrast of the images. This improved the resolution of structures such as the lamina cribrosa and optic disc drusen which are seen in low contrast in conventional images. The improved contrast of the confocal images is partly achieved by excluding light which has been scattered within the plane of focus. Structures which multiply scatter light will become less visible with confocal optics and hard exudates were found to be an example of such a structure. The cSLO and the fundus camera are seen as complementary instruments rather than as alternatives for imaging the fundus. It is envisaged that confocal imaging will enable details of the fundus to be revealed which are at present not seen in conventional images.

Fundus Oculi↗
PubMed1992

Nine generations of a family with autosomal dominant retinitis pigmentosa and evidence of variable expressivity from census records.

We present a nine generation family with autosomal dominant retinitis pigmentosa (ADRP). Evidence of blindness in the early generations, as obtained from census returns and clinical records, and examination of current patients show variable expressivity with a spectrum which ranges from asymptomatic in late life to blindness in the third decade of life. The family is not linked to any of the chromosomal locations so far described in ADRP and further illustrates the heterogeneity of the disorder.

Adolescent↗
PubMed1992

Macular disease in an elderly population.

In order to obtain more accurate information concerning the prevalence of macular diseases in an elderly population, a clinical study was undertaken on a sample of 430 members of the general population over the age of 65 years in London. Degenerative age-related macular changes were clinically visible in about 25%, and 2.8% had a lesion causing loss of visual acuity due to macular disease. Age was the only risk factor identified for age-related changes. No correlation was identified with the prevalence of hypertension, smoking, or diabetes mellitus between groups. In addition, symmetry was shown in the number of drusen, as well as their size, density and fluorescence in the central and peripheral areas between the eyes of affected subjects. The prevalence data from this study represent a baseline for the interpretation of hospital-based data and for the planning of health care.

Aged↗
PubMed1992

Recombination between rhodopsin and locus D3S47 (C17) in rhodopsin retinitis pigmentosa families.

Autosomal dominant retinitis pigmentosa (adRP) has shown linkage to the chromosome 3q marker C17 (D3S47) in two large adRP pedigrees known as TCDM1 and adRP3. On the basis of this evidence the rhodopsin gene, which also maps to 3q, was screened for mutations which segregated with the disease in adRP patients, and several have now been identified. However, we report that, as yet, no rhodopsin mutation has been found in the families first linked to C17. Since no highly informative marker system is available in the rhodopsin gene, it has not been possible to measure the genetic distance between rhodopsin and D3S47 accurately. We now present a linkage analysis between D3S47 and the rhodopsin locus (RHO) in five proven rhodopsin-retinitis pigmentosa (rhodopsin-RP) families, using the causative mutations as highly informative polymorphic markers. The distance, between RHO and D3S47, obtained by this analysis is theta = .12, with a lod score of 4.5. This contrast with peak lod scores between D3S47 and adRP of 6.1 at theta = .05 and 16.5 at theta = 0 in families adRP3 and TCDM1, respectively. These data would be consistent with the hypothesis that TCDM1 and ADRP3 represent a second adRP locus on chromosome 3q, closer to D3S47 than is the rhodopsin locus. This result shows that care must be taken when interpreting adRP exclusion data generated with probe C17 and that it is probably not a suitable marker for predictive genetic testing in all chromosome 3q-linked adRP families.

Chromosome Mapping↗
PubMed1992

Abnormal dark adaptation and rhodopsin kinetics in Sorsby's fundus dystrophy.

Scotopic visual thresholds and time courses for dark adaptation were determined in eight patients with Sorsby's fundus dystrophy. Rhodopsin regeneration also was recorded in two. All patients had poor night vision and a visible yellow deposit at the level of Bruch's membrane that was confluent in the posterior pole. In retinal regions with the yellow deposit, scotopic thresholds were elevated, the rod-cone break was delayed or indistinct, the time courses for the rod portion of the dark adaptation curve was prolonged, and rhodopsin regeneration was slow in the one patient in whom measurements were made. In regions of ophthalmoscopically normal retina, dark adaptation was affected minimally, and in one patient, rhodopsin was regenerated at a normal rate. It was hypothesized that the abnormal dark adaptation and rhodopsin kinetics might be caused by reduced metabolic exchange across a thickened Bruch's membrane.

Adult↗
PubMed1992

[The Bruch membrane and choroid. Angiography and functional characteristics in age-related changes].

Age-related changes in the retinal pigment epithelium and Bruch's membrane are believed to play an important role in the pathogenesis of age-related macular degeneration. Ophthalmoscopically visible drusen in the macular area may precede the complications causing visual loss. In addition to these localized depositions of debris in Bruch's membrane, histological methods could demonstrate linear deposits in Bruch's membrane which may also profoundly influence the development of complicated macular aging changes. It is difficult to identify linear deposits clinically, but as an indirect criterion for diffuse thickening and linear deposits in Bruch's membrane regression of the choriocapillaris with consequent prolongation of the choroidal filling phase in fluorescein angiography is suggested. This feature was observed in 26% of elderly patient. In association with these areas of regressed choroidal capillaries, loss of visual function was found in fine matrix perimetry.

Aged↗
PubMed1992

Functional loss in age-related Bruch's membrane change with choroidal perfusion defect.

During a prospective study of age-related macular degeneration, evidence of diffuse Bruch's membrane disease was sought using fluorescein angiographic evidence of a prolonged choroidal filling phase. Dark-adapted static perimetry was done on eight eyes with this angiographic sign and on six eyes with a similar number of drusen but no manifest choroidal perfusion abnormality. Scotopic threshold was measured using the Humphrey automated perimeter and fine matrix mapping. In eyes without delayed choroidal perfusion, no discrete areas of increased threshold were found compared with the background sensitivity. By contrast, in seven of the eight eyes with fluorescein angiographic evidence of prolonged choroidal filling, discrete areas of scotopic threshold elevation (up to 3.4 log units) were recorded; these corresponded closely to regions of choroidal perfusion abnormality. It was postulated that diffuse deposits of abnormal material might account for both the perfusion abnormality and functional loss by acting as a diffusion barrier between the choriocapillaris and the retinal pigment epithelium.

Aged↗
PubMed1991

Autosomal dominant retinitis pigmentosa: four new mutations in rhodopsin, one of them in the retinal attachment site.

Several mutations in the rhodopsin gene in patients affected by autosomal dominant retinitis pigmentosa (ADRP) have recently been described. We report four new rhodopsin mutations in ADRP families, initially identified as hetero-duplexed PCR fragments on hydrolink gels. One is an in-frame 12-bp deletion of codons 68 to 71. The other three are point mutations involving codons 190, 211, and 296. Each alters the amino acid encoded. The codon 190 mutation has been detected in 2 from a panel of 34 ADRP families, while the remaining mutations were seen in single families. This suggests that, consistent with a dominant condition, no single mutation will account for a large fraction of ADRP cases. The base substitution in codon 296 alters the lysine residue that functions as the attachment site for 11-cis-retinal, mutating it to glutamic acid. This mutation occurs in a family with an unusually severe phenotype, resulting in early onset of disease and cataracts in the third or fourth decade of life. This result demonstrates a correlation between the location of the mutation and the severity of phenotype in rhodopsin RP.

Amino Acid Sequence↗
PubMed1991

Histopathology of incipient fundus flavimaculatus.

A 9-year-old boy was diagnosed with fundus flavimaculatus in his left eye. The boy's fellow eye was enucleated at 16 months of age for retinoblastoma. The authors reviewed the material submitted for histopathologic examination and found that the retinal pigment epithelial cells demonstrated increased autofluorescence and increased reactivity to periodic acid-Schiff staining. Many cells had their melanin granules displaced toward the cell apex. The retinal pigment epithelial changes are consistent with previous histopathologic findings in fundus flavimaculatus and imply that the structural changes are seen in early life.

Child↗
PubMed1991

Ophthalmological screening for von Hippel-Lindau disease.

Forty seven individuals (from 16 kindreds) without prior evidence of retinal haemangiomas underwent full ophthalmological assessment as part of a comprehensive screening programme for Von Hippel-Lindau disease. Ten were known to be affected on the basis of non-ocular involvement and 37 were at 50% risk of having the abnormal gene. Seventeen angiomas were detected in 14 individuals (six affected patients and eight at risk relatives). Regular detailed ophthalmological assessment is important for all patients with von Hippel-Lindau disease and for relatives at risk of inheriting the abnormal gene.

Adult↗
PubMed1991

Surgical management of essential blepharospasm.

We have reviewed the surgical management of essential blepharospasm over the last 15 years, comparing the results from facial nerve avulsion with those from orbicularis muscle stripping. After facial nerve avulsion 50% of patients remained free of troublesome spasm for 15 months after surgery, but only 25% remained so for more than two years. Following orbicularis oculi myectomy 50% of patients were free of troublesome spasms for 30 months after surgery and 55% of patients had relief from spasm for more than two years. Secondary effects of the two procedures are compared and are found to be fewer after orbicularis myectomy. There were no major complications after either form of surgery. Botulinum toxin is the treatment of first choice for this condition. If this becomes ineffective or inconvenient, surgical treatment is warranted and should not be deferred for fear of severe side effects of treatment, since these are rare. Protractor myectomy gives longer relief from blepharospasm than facial nerve avulsion and has fewer complications. However, it is technically difficult, time consuming, and has greater peroperative morbidity. Facial nerve avulsion may therefore still have a role in selected patients.

Adult↗
PubMed1991

Genetic localisation of the RP2 type of X linked retinitis pigmentosa in a large kindred.

Genetic linkage and deletion studies have led to the proposal that there are at least two loci on the X chromosome which are responsible for X linked retinitis pigmentosa (XLRP). One locus (RP3) has been closely defined by genetic linkage and deletion analyses and localised to the region between the ornithine transcarbamylase (OTC) and chronic granulomatous disease (CYBB) loci in Xp21.1-p11.4. The other locus (RP2) has been assigned by linkage analysis alone to region Xp11.4-p11.2, but its localisation is less well defined. The results of a multipoint linkage analysis of a single large XLRP kindred using eight informative loci provide further evidence on the localisation of RP2 to this region. The maximum likelihood location of this locus shows a multipoint lod score of 7.17 close to DXS255 (in Xp11.22) and TIMP (in Xp11.3-p11.23), neither of which show recombination with RP2, in an area extending from 2 cM proximal to DXS7 to 1 cM distal to DXS14 (approximate 95% confidence limits).

Bayes Theorem↗
PubMed1991

A 3-bp deletion in the rhodopsin gene in a family with autosomal dominant retinitis pigmentosa.

Autosomal dominant retinitis pigmentosa (ADRP) has recently been linked to locus D3S47 (probe C17), with no recombination, in a single large Irish family. Other ADRP pedigrees have shown linkage at zero recombination, linkage with recombination, and no linkage, demonstrating genetic heterogeneity. The gene encoding rhodopsin, the rod photoreceptor pigment, is closely linked to locus D3S47 on chromosome 3q. A point mutation changing a conserved proline to histidine in the 23d codon of the gene has been demonstrated in affected members of one ADRP family and in 17 of 148 unrelated ADRP patients. We have sequenced the rhodopsin gene in a C17-linked ADRP family and have identified in the 4th exon and in-frame 3-bp deletion which deletes one of the two isoleucine monomers at codons 255 and 256. This mutation was not found in 30 other unrelated ADRP families. The deletion has arisen in the sequence TCATCATCAT, deleting one of a run of three x 3-bp repeats. The mechanism by which this occurred may be similar to that which creates length variation in so-called mini- and microsatellites. Thus ADRP is an extremely heterogeneous disorder which can result from a range of defects in rhodopsin and which can have a locus or loci elsewhere in the genome.

Amino Acid Sequence↗