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Biomedical subjects

A C Bird

Publications and source records attributed to A C Bird.

At least 235 records · Page 13Linked to original sources
PubMed1989

Leber's hereditary optic atrophy.

Leber described a particular type of hereditary optic atrophy in 1871. The clinical features of all cases since reported are reviewed. There is characteristically acute visual loss, circumpapillary teleangiectatic micropathy, tortuosity of the retinal vessels and oedema in the retinal nerve fibres. 85% of those affected are male, but affected fathers do not transmit the condition to their children. The exact mode of inheritance is still obscure but it is suggested that inheritance may be mitochondrial; enlarged subsarcolemmal mitochondria in LOA patients have been described. Colour vision defects are observed not only in patients, but also in presumed carriers. Electrophysiological investigations demonstrate optic nerve damage, but are not indicative of any particular pathology. It has been reported that in many cases of LOA the severity of the disease is related to tobacco smoking. Increased cyanocobalamin blood levels in patients and increased cyanide blood levels support this hypothesis.

Electroretinography↗
PubMed1989

Ophthalmological results from a placebo controlled comparative 3-dose ivermectin study in the treatment of onchocerciasis.

One hundred and ninety eight patients with moderate to heavy infection with Onchocerca volvulus and with eye involvement in most, were allocated randomly to treatment with 100, 150 or 200 mcg/kg body weight of ivermectin or placebo given as a single oral dose in a double-blind dose finding study. The patients were drawn from an area under over ten years of vector control in Northern Ghana by the Onchocerciasis Control Programme, OCP. They underwent detailed clinical, laboratory and ophthalmological examination before treatment and in the review period of one year in hospital. Ivermectin given in a dose of 100, 150 or 200 mcg/kg eliminated microfilariae similarly slowly over 3-6 months and was associated with inflammatory reaction in the anterior segment which resolved without treatment. No changes in the fundus of the eye was detected by fluorescein angiography and no no-table other adverse eye reaction was observed. The ceiling of therapeutic activity of ivermectin in the eye is therefore put at 100 mcg/kg which is lower than the level fo 150 mcg/kg found in the skin. The apparent discrepancy may be due to different dose requirements on account of different mechanisms of action of ivermectin at the two sites. In the skin there is active killing while in the eye it is presumed there is a passive elimination of microfilariae.

Adolescent↗
PubMed1989

Degenerative changes in a retina affected with autosomal dominant retinitis pigmentosa.

The eyes of a 17-year-old male donor who was affected with autosomal dominant retinitis pigmentosa with variable expressivity have recently become available for study. Initial macroscopic examination of the fundus revealed bone spicules located in 180 degrees of the postequatorial fundus centered on the inferonasal quadrant. Light microscopic examination of the retina showed degeneration within each quadrant characterized by an absence of rods and cones in the equatorial areas, and the presence of photoreceptors in the more peripheral and central retina. Ultrastructural examination disclosed photoreceptors that were abnormal in all regions when compared to a control eye from a 26-year-old donor. Intact rods were restricted to the peripheral quadrants, and intact cones were identified in the fovea and far periphery. In areas of intermediate degeneration, many outer segments were either shortened and disorganized or absent. Regions of severe degeneration were characterized by the complete loss of the photoreceptors and apposition of the external limiting membrane to the retinal pigment epithelium. The density of rods and cones was found to be substantially lower than normal in all regions. In areas of relatively intact photoreceptor outer segments, we found ultrastructural evidence of recent phagocytic activity, and fluorescence microscopy revealed no unusual accumulation of lipofuscin within the pigment epithelium or subepithelial debris. The choroid and inner retina were normal throughout the eye. The normal condition of the choroid, retinal pigment epithelium, and inner retina implies that the primary disorder resides within the photoreceptor cell.

Adolescent↗
PubMed1988

Ocular fundus lesions in divers.

Retinal fluorescein angiography was used to examine the ocular fundi of 84 divers. The retinal capillary density at the fovea was low and microaneurysms and small areas of capillary nonperfusion were seen. The divers had significantly more abnormalities of the retinal pigment epithelium than a comparison group of non-divers. Furthermore, the prevalence of fundus abnormality was related to length of diving history. All observed changes were consistent with the obstruction of the retinal and choroidal circulations. Such obstruction could be due either to intravascular bubble formation during decompression, or to altered behaviour of blood constituents and blood vessels in hyperbaric conditions.

Adolescent↗
PubMed1988

Electrophysiologic studies in birdshot chorioretinopathy.

We investigated retinal function in 16 patients with birdshot chorioretinopathy. Consistent abnormalities of dark adaptation, color vision, visual field, electro-oculography, electroretinography, and visual-evoked cortical potentials were found. They included raised thresholds of dark adaptation, acquired dyschromatopsia, mainly of the blue-yellow type, an electroretinogram with reduced amplitude, increased latency of the b-wave and absent oscillatory potentials, an abnormal electro-oculogram, and in many a marked disturbance in the pattern reversal visual-evoked cortical potential. The a-wave of the electroretinogram, the fast oscillations of the standing potential, and the flash visual-evoked cortical potential were well preserved. The nature of the abnormalities suggests that dysfunction was caused by inner retinal disease. Little evidence indicated outer retinal dysfunction resulting from choroidal inflammation.

Adult↗
PubMed1988

Detection of the carrier state of X-linked retinoschisis.

We determined the extent of suppressive rod-cone interaction in 11 obligate carriers and eight potential carriers of X-linked retinoschisis from eight families. Despite otherwise normal ophthalmoscopic and functional testing, all of the obligate heterozygous carriers demonstrated a complete absence of normal rod-cone interaction. Of the potential heterozygous carriers, three had normal rod-cone interactions, two had no detectable interaction, and two yielded technically unsatisfactory results. This lack of rod-cone interactions allows heterozygous individuals to be identified clinically and has implications concerning the origin of this inherited disorder.

Flicker Fusion↗
PubMed1988

The pathogenesis of tears of the retinal pigment epithelium.

We compared drusen in the fellow eye of patients with unilateral retinal pigment epithelial tears with those in an age- and sex-matched group of patients with unilateral primary neovascular disciform lesions. In the fellow eye of patients with tears, drusen were more confluent and manifested less fluorescence on angiography than in the comparison group. These observations are in accord with the concept that Bruch's membrane represents a significant barrier to fluid flow, and that fluid beneath detached pigment epithelium is derived in part or wholely from the pigment epithelium.

Aged↗
PubMed1988

Juxtapapillary choroidal neovascularization in older patients.

We studied retrospectively 55 eyes with juxtapapillary choroidal neovascularization in 42 patients over the age of 50 years. In all but four lesions, the choroidal neovascularization was undetected, causing the choroidal new vessel complexes to be ill defined, discontinuous, and show irregular dye leakage on fluorescein angiography. Growth of the lesion was unpredictable. Visual loss occurred in eight of 16 eyes during the first six months of follow-up. Recurrent neovascularization after photocoagulation originated in some patients from outside the pretreatment subretinal complex. Of the 15 patients with bilateral involvement, 13 had juxtapapillary lesions. Fellow eyes in patients with unilateral juxtapapillary lesions showed no predisposing abnormality at or near the nerve head. The prevalence, density, and fluorescein angiographic characteristics of drusen were different from those in age- and sex-matched patients with macular neovascularization.

Aged↗
PubMed1988

Treatment of chronic macular edema with acetazolamide.

In a prospective study, 41 patients with documented chronic macular edema of various causes were entered into a therapeutic trial of acetazolamide sodium, a carbonic anhydrase inhibitor. Each patient received a five-cycle cross-over regimen of treatment/no treatment with a further two cycles of cross-over with another diuretic, cyclopenthiazide, which does not inhibit carbonic anhydrase. At each cross-over patients were examined for evidence of macular edema. Sixteen of 41 patients showed a reproducible response to acetazolamide with partial or complete resolution of edema and improvement of visual acuity. The therapeutic effect occurred in more than half of the patients with inherited outer retinal disease or uveitis, but in none with primary retinal vascular disorders. There was no correlation between the response to treatment and the extent or duration of the edema. No influence of cyclopenthiazide on macular edema was detected.

Acetazolamide↗
PubMed1988

Repair after tears of the retinal pigment epithelium.

Sixty-three eyes (in 59 patients) with tears of detached retinal pigment epithelium have been studied for a period of up to 10 years after the acute event. In the majority of cases a plaque of fibrous tissue was laid down gradually in the bed of the tear. In a few eyes the inner surface of Bruch's membrane appeared to remain relatively unaltered for up to 2 years, and in four eyes it was recovered with pigmented tissue resembling normal retinal pigment epithelium. These and other changes progressively obscured the distinctive feature of the original lesion; the nature of the original lesion was evident at 6 months in all cases, by 1 year it was recognisable in 94 per cent, by 2 years in 77 per cent and by 6 years in none. Choroidal neovascularisation was detected or suspected in one third of cases in the acute stages and developed in others weeks to months after the acute event. Alteration of the morphology occurred more quickly, and there was greater scarring, in those with new vessels or significant blood in the subretinal space, when compared with those without such features. Visual acuity was surprisingly good in many patients immediately after the tear. However, loss of vision accompanied the reactive tissue remodelling, and no case had long term retention of good visual acuity.

Aged↗
PubMed1988

Sorsby's pseudoinflammatory macula dystrophy--Sorsby's fundus dystrophies.

The findings are presented on the updated Kempster pedigree with Sorsby's fundus dystrophy. The study confirms the features described in other families: autosomal dominant inheritance with complete penetrance, loss of central vision due to subfoveal ingrowth of new vessels, and progressive peripheral chorioretinal atrophy. By contrast to other reports the family in the current study have peripheral retinal dysfunction, a deposit of a subretinal yellow material throughout the fundus and a tritan colour defect, all prior to the loss of central vision; in some patients there was loss of central vision from atrophic disease, rather than from ingrowth of subretinal new vessels; and, there was a different temporal progression of the central subretinal neovascular complex. These features suggest the possibility of genetic heterogeneity.

Adult↗
PubMed1988

Clinical investigation of retinitis pigmentosa.

The diagnostic features and future research directions of retinitis pigmentosa were documented in this update and review of the subject. An extensive and current bibliography is provided.

Cell Survival↗
PubMed1988

Sickle cell retinopathy in Jamaican children: further observations from a cohort study.

Serial retinal examinations were performed in children aged 5 years and older and fluorescein angiography/angioscopy in children 6 years and older participating in a cohort study of sickle cell disease. There were 1229 patient years of observation among 389 children aged 5-13 years. Peripheral retinal vessel closure was present in approximately 50% of children with SS and SC genotypes at age 6 years and increased to affect 90% of children by age 12 years. A matched pair analysis, comparing groups with minimal and complete closure, indicated that complete closure was associated with significantly lower total haemoglobin and fetal haemoglobin levels and significantly lower weight in SS disease, whereas in SC disease the risk factors appeared to be high mean cell volume and low platelet count. Proliferative retinopathy was rare, occurring only once in an 8-year-old boy with SC disease, despite 592 patient years of observation in children over this age.

Adolescent↗
PubMed1988

Bilaterality of tears of the retinal pigment epithelium.

Eyes with tears of detached retinal pigment epithelium have been studied for up to 10 years following the acute event. In a retrospective study it has been determined that such a lesion in one eye implies a high risk of a similar event occurring in the fellow eye. Patients with loss of vision in their second eye as a result of a pigment epithelial tear were also studied; in 10 of 22 patients a similar lesion could be identified in the first eye. These observations suggest that these patients have specific changes at the level of Bruch's membrane which predispose to this particular manifestation of age related macular disease.

Age Factors↗
PubMed1988

A diurnal rhythm in opsin content of Rana pipiens rod inner segments.

Quantitative electron microscope immunocytochemistry, employing an antibody specific to opsin, was used to evaluate the amount and location of opsin in Rana pipiens rod photoreceptors throughout a 24 hr light/dark cycle. We found a distinct diurnal rhythm in the density of anti-opsin labeling of the rough endoplasmic reticulum (RER) and Golgi apparatus in the myoid region of the rod inner segment. Opsin labeling of these organelles was lowest at light onset, increasing thereafter by three- to four-fold, and remained high until 2 hr into the dark phase. A fall in labeling density occurred within the following 4 hr, and remained low for the remainder of the dark phase. Our finding of a diurnal rhythm regulating inner segment opsin transport in Rana pipiens contrasts with published observations on outer segment membrane turnover, since it has been shown that the rates of disc formation and disc shedding are governed by environmental lighting alone in this species. These results imply that there is opsin pooling in the inner segment during the first 14 hr of a 24 hr light/dark cycle; thereafter the loss of inner segment opsin due to mobilization of this protein from the Golgi exceeds the rate of formation of new opsin. There was no evidence of accumulation of opsin-containing vesicles near the cilium or in the ellipsoid just prior to light onset. At light onset, prominent opsin labeling was identified at the proximal portion of the outer segment in regions separate from the disc stack. In two separate experiments, additional groups of frogs were killed around the time of light onset and were examined by conventional transmission electron microscopy. Disordered disc membranes were seen at the base of the outer segment which were not in register with the disc stack. These disordered membranes were observed as early as 2 hr before light onset, and were no longer observed by 1 hr after light onset. We suggest that these disordered membranes reflect a step in the biogenesis of new discs, serving as a pool of membrane that forms during the later part of the dark cycle. It appears that light onset triggers the ordering of neatly registered discs from this new membrane, rather than assembly of new membrane from pooled transport vesicles in the inner segment.

Animals↗
PubMed1988

The potential usefulness to research of retina obtained by biopsy.

Retinal biopsy has been performed on normal rabbits and dogs. It was shown that retinal samples could be obtained by internal and external routes in rabbits, but in dogs inability to achieve adequate vitrectomy precluded useful retinal biopsy by the internal route. A single external biopsy specimen of 3 mm diameter was more than adequate to undertake standard histopathological examination, immunocytochemical experiments and determination of cyclic nucleotide levels. The quality of the micrographs, immunocytochemical labelling of rhodopsin and phosphodiesterase, and cyclic nucleotide analyses were similar to those obtained with retinas from freshly enucleated eyes. The surgical exercise was well tolerated by most eyes and does not preclude serial biopsies being undertaken. It is concluded that retinal biopsy provides material of sufficient quantity and quality to satisfy many laboratory needs in retinal research.

Animals↗
PubMed1987

The dark choroid in posterior retinal dystrophies.

Fourteen families with genetically determined posterior retinal dystrophies were studied by fluorescein angiography. With one exception, the families could be segregated into two clearly defined categories, one in which every member had a dark choroid, and one where each had a light choroid. This implies that the fluorescein angiography provides a means of subdividing certain of these disorders into more specific disease groups.

Choroid↗