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Biomedical subjects

F A Billson

Publications and source records attributed to F A Billson.

At least 91 records · Page 5Linked to original sources
PubMed1987

The differential effect of optic nerve disease on pattern and focal electroretinograms.

We studied nine cases of retrobulbar neuritis with confirmed multiple sclerosis and six cases of optic atrophy from other causes. Pattern and focal electroretinograms (macular ERGs) were recorded with high (400 cd/m2) and low (40 cd/m2) intensity stimuli. Contrast sensitivity was also measured with a simple printed test. Luminance was not markedly important. High spatial frequency contrast sensitivity was significantly correlated with pattern ERG amplitude. Pattern and focal ERG amplitude ratio was usually reduced, but the effect was not correlated with contrast sensitivity or large enough to be useful clinically. In optic atrophy the pattern ERG (PERG) was clearly more severely reduced than the focal ERG (FERG). In retrobulbar neuritis both ERGs were equally and more severely reduced even though the visual losses were less. In unilateral cases the PERG increased then decreased after the initial attack, as previously described (Arden et al., 1982). The results suggest that retinal layers beyond the ganglion cells may be affected in retrobulbar neuritis, but proximally generated, pattern-specific ERG components are selectively lost in optic atrophy.

Electroretinography↗
PubMed1987

Age-related macular degeneration: ultrastructural studies of the relationship of leucocytes to angiogenesis.

We describe the ultrastructural features of subretinal neovascularisation associated with the pathogenesis of age-related macular degeneration (AMD). The choroidal origin of new vessels was confirmed, and ultrastructural details are presented. Serial sectioning of new vessels revealed a relationship between leucocytes and neovascular structures. The results are discussed in the context of the previously established role of leucocytes in angiogenesis. Our results provide circumstantial evidence, based on morphological observations, for the involvement of leucocytes in the promotion of neovascular proliferation and exudation from new vessels.

Aged↗
PubMed1986

Macular electroretinograms and contrast sensitivity as sensitive detectors of early maculopathy.

Eighteen patients with early maculopathies of various etiologies were tested with pattern and focal electroretinograms (macular ERGs), with high (400 cd/M2) and moderate (40 cd/M2) stimulus intensities and a four-alternative forced choice (4AFC) contrast sensitivity test in addition to intensive clinical examinations. High spatial frequency contrast sensitivity loss on the 4AFC test was the most striking and consistent feature of all cases. The only eyes not outside normal contrast sensitivity limits were three in which diagnosis was uncertain and the patients had not recognized any problem, including two marginal solar burns. Maculopathy also substantially reduced macular ERG amplitudes. Criterion scores on these tests separated patients from normals more effectively than other noninvasive procedures and only missed one eye detected by contrast sensitivity. Latencies were affected but the delays were of no clinical significance in the individual case. Stimulus intensity was not critical. The results indicate that contrast sensitivity testing and macular ERGs are very reliable indices of central visual dysfunction at a stage when visible macular changes are too subtle for confident diagnosis. Contrast sensitivity has appeal because of its reliability, objectivity, simplicity, and noninvasive nature. It is equally applicable to children and adults. Pattern and focal ERGs can establish that the visual deficit has a retinal origin and can provide the most reliable objective confirmation.

Electroretinography↗
PubMed1986

Corneal graft survival: a retrospective Australian study.

Four hundred and forty-eight consecutive corneal grafts are analysed and their survival calculated using the actuarial life-table method. Overall survival at two years is 81 +/- 4% and at five years is 65 +/- 5%. Within diagnostic subgroups keratoconus has the best prognosis. Previous graft failure and recipient corneal vascularization are shown to have a negative effect on graft survival. Sex of patient, urgency of operation and use of combined procedures do not affect survival and second regrafts fare no worse than first regrafts. The use of the actuarial life-table method of analysing graft survival is discussed and its importance emphasized.

Actuarial Analysis↗
PubMed1986

Optic nerve hypoplasia: changing perspectives.

Optic nerve hypoplasia, having once been regarded as exceedingly rare, is now regarded as one of the major causes of visual loss in infancy. Recognition of subtle forms and segmental forms of optic nerve hypoplasia are important in explaining the evaluation of subnormal vision, and have an added significance in the recognised associations of central nervous system anomalies including abnormalities of the endocrine system. These changing clinical perspectives are reviewed, together with a discussion of the pathogenesis of optic nerve hypoplasia in the light of cell death and nerve fibre degeneration seen in normal development of the neural visual system.

Anticonvulsants↗
PubMed1985

Human fetal optic nerve: overproduction and elimination of retinal axons during development.

We have estimated the number of axons in the optic nerves of human fetuses ranging in gestational age from approximately 10 to 33 weeks. At 10-12 weeks of gestation there were an estimated 1.9 million axons in the optic nerve. A peak count of 3.7 million axons was obtained from a specimen of 16-17 weeks gestation. The estimated number of axons then declined, stabilizing at an estimated 1.1 million axons by about week 29 of gestation. This figure is in close agreement with an estimate of 1.1-1.3 million optic axons in the human adult optic nerve. The results indicate that at least 70% of optic axons generated during development of the primary visual pathway are lost during fetal life. Part of this loss probably occurs as a result of the refinement of the terminal distribution of ganglion cell projections within their target nuclei. The significance of the relatively prolonged period of axonal loss is discussed.

Axons↗
PubMed1985

Development of the human retina: patterns of cell distribution and redistribution in the ganglion cell layer.

Neurogenesis in the ventricular layer and the development of cell topography in the ganglion cell layer have been studied in whole-mounts of human fetal retinae. At the end of the embryonic period mitotic figures were seen over the entire outer surface of the retina. By about 14 weeks gestation mitosis had ceased in central retina and differentiation of photoreceptor nuclei was evident within a well-defined area which constituted about 2% of total retina area. This area was approximately centered on the site of the putative fovea, identified by the exclusive development of cone nuclei at that location. The area of retina in which mitosis had ceased increased as gestation progressed. By mid-gestation mitosis in the ventricular layer occupied about 77% of the outer surface of the retina and by about 30 weeks gestation mitosis in the ventricular layer had ceased. Cell density distributions in the ganglion cell layer were nonuniform at all stages studied (14-40 weeks). Densities were highest at about 17 weeks gestation, and by mid-gestation the adult pattern of cell topography was present with maps showing elevated cell densities in posterior retina and along the horizontal meridian. Cell densities generally declined throughout the remainder of the gestation period, except in the posterior retina, where densities in the perifoveal ganglion cell layer remained high during the second half of gestation. There is a rapid decline in cell density in the foveal ganglion cell layer toward the end of gestation, and it is suggested that the persistence of high densities in the perifoveal region may be related to migration of cells away from the developing fovea. The total population of cells in the ganglion cell layer was highest (2.2-2.5 million cells) between about weeks 18 and 30 of gestation. After this the cell population declined rapidly to 1.5-1.7 million cells. It is suggested that naturally occurring neuronal death is largely responsible for this decline.

Cell Count↗
PubMed1985

Visual deprivation in infancy and childhood: clinical aspects.

The effects of visual deprivation in 15 patients (14 children and one adult) were studied. The age of onset of deprivation and the significance of final visual outcome are discussed. Results indicate that a critically sensitive period in visual development occurs between approximately four months and three years of age. A period of plasticity, when the effects of deprivation are more responsive to therapy, follows. Age of onset of deprivation was found to be most important, but in addition loss of accommodation in association with deprivation may be a significant factor in the development of amblyopia.

Adult↗
PubMed1984

Tyrosinaemia II.

Four cases of tyrosinaemia type II (Richner-Hanhart syndrome) are reported. This syndrome consists of corneal erosions, palmar and plantar hyperkeratoses, and sometimes mental retardation. Presentation with photophobia and dendritic corneal ulceration or circumscribed palmoplantar keratoderma should alert the physician to the possible diagnosis of tyrosinaemia II. Early diagnosis is important, as the clinical picture can be modified by dietary restriction.

Adult↗
PubMed1984

Dissociated vertical deviation: evidence of abnormal visual pathway projection.

Abnormalities in visually evoked responses have been used to demonstrate abnormal optic nerve fibre projections in human albinos, who have anomalous nystagmoid movements. Using visually evoked potentials we tested the hypothesis that patients with dissociated vertical deviation (another group with anomalous nystagmoid movements) may have abnormal visual evoked responses similar to those of albinos. Patients with dissociated vertical deviation (both unilateral and alternating), patients with congenital esotropia without dissociated vertical deviation, and normal subjects were investigated. The results showed a very high incidence of abnormal visual evoked responses in patients with dissociated vertical deviation, while recordings from the other groups were normal. As well as suggesting the possibility of abnormalities of optic nerve fibre projections, the visual evoked responses showed a marked increase in latency in all patients with dissociated vertical deviation. These results occurred regardless of the visual acuity or amblyopia of the eyes tested. The possible existence of abnormal pathway projection in the presence of dissociated vertical deviation is discussed.

Evoked Potentials, Visual↗
PubMed1984

Vitrectomy and photocoagulation in the management of serous detachment associated with optic nerve pits.

Two cases of serous detachment of the retina associated with congenital pits of the optic nerve were successfully treated with photocoagulation, vitrectomy and gas tamponade. The rationale of management and the results are discussed. It is suggested that this treatment deserves further study to see if early intervention will favourably affect the return of macular function, particularly in cases of optic nerve pits where the serous detachment is of short duration and fixed structural changes at the macula have not occurred.

Adolescent↗
PubMed1983

Microsurgery of choroidal melanoma--surgical techniques of local excision.

Six cases of malignant choroidal melanoma were treated by microsurgical excision under hypotensive anaesthesia with follow-up periods varying from four months to four years. This paper presents the case for local excision of malignant choroidal melanoma in the light of the current controversy surrounding the management and natural history of choroidal melanoma. The indications for surgery, techniques, and results are described. Vision was preserved best in tumours with diameters of less than 10 mm. No deaths and no evidence of extraocular recurrence occurred.

Aged↗
PubMed1983

Ganglion cell topography in human fetal retinae.

Whole-mounted human fetal retinae of gestational ages 14-40 weeks have been studied. These preparations clearly show the distribution of retinal ganglion cells or their precursors across the retina, and the pattern of the retinal vessels and vessel primordia. The ganglion cell layer is present at 14 weeks of gestation and distribution of cells in this layer (ganglion cell precursors) is at first uniform. Ganglion cell density gradients that foreshadow those seen in the adult retina become evident by about 20 weeks gestation. Both mature ganglion cells and precursor cells are present in retinae at about 24 weeks and precursor cells are still seen in the peripheral parts of the retina at about 30 weeks of gestation. The development of mature ganglion cells would appear to coincide with the establishment of retinal circulation, and proceeds in centrifugal sequence from central retinal.

Gestational Age↗
PubMed1981

Monocular axial myopia associated with neonatal eyelid closure in human infants.

We studied eight infants who developed unilateral axial myopia associated with neonatal eyelid closure. Clinical findings and ultrasonographic biometric measurements suggested that axial elongation of the eye may occur as a result of neonatal eyelid closure, a finding similar to that for experimental myopia produced in neonatal animals after eyelid fusion. Early treatment of eyelid occlusion in the neonate may prevent axial myopia and subsequent anisometropic amblyopia.

Blepharoptosis↗