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Biomedical subjects

A G Robson

Publications and source records attributed to A G Robson.

16 recordsLinked to original sources
PubMed2006

Functional characterisation and serial imaging of abnormal fundus autofluorescence in patients with retinitis pigmentosa and normal visual acuity.

AIM: To characterise and monitor abnormal fundus autofluorescence (AF) in patients with retinitis pigmentosa (RP) who have good visual acuity. METHODS: 21 patients with a clinical diagnosis of RP were examined. All had rod-cone dystrophy (ISCEV standard electroretinograms (ERGs)), visual acuity of 6/9 or better, and manifested a parafoveal ring of high density fundus AF. Repeat AF imaging was performed after periods of between 2 years and 5 years in 12 patients. Pattern ERG (PERG) and multifocal ERG (mfERG) were performed in 20 cases. Visual fields (VF), photopic and scotopic fine matrix mapping and small field PERGs were performed in representative cases. RESULTS: The rings of high density AF varied in size between patients (from 4 degrees -16 degrees diameter). MfERGs showed relative preservation over the central macular area, correlating with the size of AF ring and with PERG and psychophysical data. Progressive constriction of the AF ring was demonstrated at follow up in three patients. Serial PERG, mfERG, and VFs, performed in one of these cases, showed evidence of deterioration concordant with ring constriction. CONCLUSIONS: High density rings of AF, seen in some patients with RP with good visual acuity, demarcate areas of preserved central photopic function. MfERGs correlate with the area encircled by high density AF and the PERG data. The size of the ring of AF can show progressive constriction accompanied by increasing macular dysfunction.

Adolescent↗
PubMed2005

Retinal dysfunction and refractive errors: an electrophysiological study of children.

AIMS: To evaluate the relation between refractive error and electrophysiological retinal abnormalities in children referred for investigation of reduced vision. METHODS: The study group comprised 123 consecutive patients referred over a 14 month period from the paediatric service of Moorfields Eye Hospital for electrophysiological investigation of reduced vision. Subjects were divided into five refractive categories according to their spectacle correction: high myopia (< or = -6D), low myopia (>-6D and < or = -0.75D), emmetropia (>-0.75 and <1.5D), low hyperopia (> or = 1.5 and <6D), and high hyperopia (> or = 6D). Patients with a specific diagnosis at the time of electrophysiological testing were excluded. Only the first member of any one family was included if more than one sibling had been tested. All tests were performed to incorporate ISCEV standards, using gold foil corneal electrodes where possible. In younger patients skin electrodes and an abbreviated protocol were employed. RESULTS: The mean age of patients was 7.1 years with an overall incidence of abnormal electrophysiological findings of 29.3%. The incidence of abnormality was higher in high ametropes (13/25, 52%) compared to the other groups (23/98, 23.5%). This difference was statistically significant (chi2 test, p = 0.005). There was also a significant association between high astigmatism (>1.5D) and ERG abnormalities (18/35 with high astigmatism v 20/88 without, chi2 test, p = 0.002). There was no significant variation in frequency of abnormalities between low myopes, emmetropes, and low hyperopes. The rate of abnormalities was very similar in both high myopes (8/15) and high hyperopes (5/10). CONCLUSIONS: High ametropia and astigmatism in children being investigated for poor vision are associated with a higher rate of retinal electrophysiological abnormalities. An increased rate of refractive errors in the presence of retinal pathology is consistent with the hypothesis that the retina is involved in the process of emmetropisation. Electrophysiological testing should be considered in cases of high ametropia in childhood to rule out associated retinal pathology.

Adolescent↗
PubMed2005

Electrophysiological characterisation and monitoring in the management of birdshot chorioretinopathy.

AIMS: To characterise patients with birdshot chorioretinopathy (BCR) clinically and electrophysiologically in order to monitor changes in retinal function before and after treatment with corticosteroids and/or immunosuppression. METHODS: 18 patients with BCR were characterised clinically and electrophysiologically. Serial studies were performed on 14 patients in order to monitor changes in retinal function before and after treatment with corticosteroids and/or immunosuppression. RESULTS: Most patients presented with characteristic subretinal pale spots, were HLA-A29 positive, and had diverse signs of ocular inflammation. Various electrophysiological abnormalities were present. Moderately severe bilateral pattern electroretinogram (PERG) abnormalities at presentation were common, reflecting macular dysfunction. Cone mediated 30 Hz flicker electroretinograms (ERGs) were consistently delayed before treatment, and were the most sensitive parameter of retinal dysfunction. Scotopic maximal ERG responses were abnormal in 13 patients; 10 had an electronegative maximal ERG or a reduced b:a ratio in one or both eyes. Single flash photopic ERGs were less often and less severely affected. Photopic ON and OFF ERG responses often revealed predominant ON response b-wave abnormalities with relative OFF response preservation. ERGs improved in treated cases, sometimes preceding clinical signs of recovery. Pattern ERG improvements occurred, possibly reflecting the resolution of macular oedema. CONCLUSIONS: The ERG data confirm that BCR frequently affects inner retinal function of cone and rod systems. Clinical features were not reliable indicators of functional deterioration or recovery. Objective electrophysiological assessment of retinal function demonstrated improvement following treatment and provides a reliable method of monitoring treatment efficacy, enabling management decisions to be taken with greater confidence and allowing early initiation or modification of treatment.

Adult↗
PubMed2005

Unilateral electronegative ERG of non-vascular aetiology.

BACKGROUND: Full field and pattern electroretinograms (ERG, PERG) are performed to assess generalised retinal function and macular function, respectively. An (electro) negative full field ERG usually describes an ISCEV standard maximal response in which the b-wave is smaller than a normal or minimally reduced a-wave and indicates dysfunction that is post-phototransduction. The most common cause of a unilateral negative ERG is central retinal artery occlusion (CRAO) or birdshot chorioretinopathy (BCR). This study examines the clinical and electrophysiological features of patients with unilateral negative ERG who do not have CRAO or BCR. METHODS: 12 patients were ascertained with a unilateral negative ERG in whom a vascular aetiology and BCR were excluded. Most presented with symptoms of central retinal dysfunction. In 11 of the 12 patients additional long duration photopic stimuli were used to test cone system ON and OFF responses. RESULTS: All 12 patients had unilateral electronegative bright flash full field ERGs indicating total or relative preservation of rod photoreceptor function, but dysfunction post-phototransduction. Seven of these patients had non-specific inflammatory changes in the eye with the negative ERG. Six patients, including five with inflammatory signs, had involvement of the cone ON response with complete preservation of cone OFF responses. A further three patients showed evidence of cone ON response abnormality with less severe OFF response involvement. CONCLUSION: The ERGs in this heterogeneous group of patients predominantly showed post-phototransduction involvement of the ON pathways. Sparing of the cone OFF response was often observed. The majority of patients had signs of previous inflammation and it is speculated that these highly unusual unilateral changes may be mediated via an autoimmune mechanism.

Adult↗
PubMed2004

Juvenile neuronal ceroid lipofuscinosis (Batten disease) CLN3 mutation (Chrom 16p11.2) with different phenotypes in a sibling pair and low intensity in vivo autofluorescence.

BACKGROUND: The neuronal ceroid lipofuscinoses (Batten disease) are a heterogeneous group of autosomal recessively inherited disorders causing progressive neurological failure, mental deterioration, seizures and visual loss secondary to retinal dystrophy. The juvenile type is of special interest to the ophthalmologist as visual loss is the earliest symptom of the disorder. HISTORY AND SIGNS: We present two siblings with severe retinal dystrophy due to juvenile Batten disease. Sibling A (age 10) presented with visual loss, photophobia and night blindness, starting at age 4. His vision was perception of light by the age of 10.5 years. Fundus examination revealed severe pigmentary retinopathy. Sibling B (age 7) presented with night vision difficulties. Fundus examination revealed a bull's eye maculopathy with minimal peripheral atrophic changes. In vivo autofluorescence level was found to be very low. Electroretinography (ERG) showed generalized retinal dysfunction involving both cone and rod systems, with an electronegative maximal response. In both siblings vacuolated lymphocytes were found on a peripheral blood film and on molecular genetic testing both were homozygous for the commonly reported 1.02-kb deletion of the CLN3 gene. THERAPY AND OUTCOME: Although there is no effective treatment, the early diagnosis allowed accurate genetic and social counseling. CONCLUSIONS: Juvenile Batten disease should be considered in children with a retinal dystrophy, especially where there is a bull's eye maculopathy and an abnormal full field ERG. The novel finding of very low in vivo autofluorescence is consistent with histopathological studies and may be secondary to photoreceptor cell loss.

Blindness↗
PubMed2002

Scalp VEPs and intra-cortical responses to chromatic and achromatic stimuli in primates.

We propose asimple method of monitoring separate visual pathways inlightly sedated monkeys using chromatic and achromatic gratings of low contrast, which are known to activate predominantly either parvo- or magno-systems. The scalp Visual Evoked Potentials (VEPs) are compared with simultaneously recorded intra-cortical VEPs which in turn are compared with multi-unit and single-unit responses. At isoluminance, the onset of low contrast, coarse chromatic square wave spatial profile gratings generates negative scalp VEPs which exhibit properties consistent with the activation of sustained, parvocellular-chromatic mechanisms (e.g. low-pass spatio-temporal characteristics). In monkeys, most components of chromatic onset VEPs have latencies comparable to neuronal activity within the supragranular layers of V1. Corresponding coarse achromatic gratings elicit positive VEPs which exhibit properties consistent with the activation of transient-type magnocellular mechanisms (e.g. temporal tuning to higher temporal frequencies) and which have a more complex morphology. Achromatic onset VEPs may contain early components of similar timing to activity recorded in monkey V1, but later components cannot be related to V1 generators; other sources are not known. Achromatic reversal VEPs are similar to achromatic onset, chromatic reversal and both chromatic and achromatic offset VEPs and all differ from chromatic onset VEPs. It is observed that early components of scalp-recorded chromatic-onset VEPs are related in time to some intra-cortical potentials. These VEPs are generated by low spatial frequencies and have low pass temporal characteristics. Other scalp potentials, apparently unrelated to V1 field potential activity must be generated by other sources such as extra-striate areas.

Animals↗
PubMed2001

Short term variability of single breath carbon monoxide transfer factor.

BACKGROUND: When monitoring patients with chronic lung disease it is important to distinguish genuine changes in gas transfer over time from natural variability. This study aims to define the coefficient of repeatability for routine measurements of single breath transfer factor (TCO) and transfer coefficient (KCO). METHODS: Sixty eight subjects (32 with emphysema, 36 healthy volunteers) had TCO measured twice at a mean (SD) interval of 7.5 (1.3) days. On each occasion a standard protocol (conforming to BTS guidelines) was followed, comprising duplicate measurements satisfying standard technical criteria. The mean of these duplicates was recorded. For the pooled data changes in TCO and KCO between study days were expressed as coefficient of repeatability. RESULTS: The coefficient of repeatability was +/-1.60 mmol/min/kPa for TCO and +/-0.24 mmol/min/kPa/l for KCO. Correcting TCO and KCO for prevailing barometric pressure or carboxyhaemoglobin level made no significant difference to the results. CONCLUSIONS: The quoted limits for variability in gas transfer over time are valid for a wide range of clinically relevant values. Changes in TCO and KCO greater than these limits are unlikely to arise from natural variation.

Adult↗
PubMed2000

Laboratory assessment of fitness to fly in patients with lung disease: a practical approach.

To identify patients with respiratory disease, who may be at risk of developing respiratory distress during commercial air travel, a hypoxia inhalation test (HIT) can be performed. This paper reports our experience of using such a test combined with an interpretation algorithm in a routine respiratory function laboratory. Twenty-eight patients were studied. Baseline oxygen saturation (Sa,O2) was measured using a pulse oximeter. If Sa,O2 was < 90% no HIT was performed and the patient was assessed as unfit for air travel. If baseline Sa,O2 was > or = 90% an HIT was performed by the patient breathing through a 35% Venturi mask supplied with 100% nitrogen which reduced inspiratory oxygen fraction to 15.1+/-0.2%. Results were interpreted using a locally derived algorithm, and validation was attempted using a questionnaire to investigate subsequent symptoms during travel. All patients tolerated the assessment well. Twenty-two patients were assessed as "fit to fly" with a further two patients "fit to fly with supplemental O2". Four patients were considered unfit to fly. Hypoxic response could not be predicted from either forced expiratory volume in one second, or pretest saturation. Validation of such protocols is difficult, but the hypoxia inhalation test may be a useful tool for predicting hypoxia during air travel in patients with chronic respiratory disease.

Aerospace Medicine↗
PubMed1998

Macular pigment and the colour-specificity of visual evoked potentials.

A modified Moreland anomaloscope was used to examine two subjects, one with dense macular pigment, the other with relatively light pigmentation. Chromatic visual evoked potentials (VEPs) were elicited from these two subjects using coarse, isoluminant gratings of different sizes. Colour-specificity was verified by comparing chromatic onset VEPs (reflecting sustained activity) with chromatic reversal VEPs (reflecting mainly transient activity) and also by Fourier analysis (colour-specific responses are dominated by the fundamental, transient activity by the second harmonic). Achromatic (transient-type) intrusions, produced by large blue-green gratings could be related to the extent of subject-specific macular pigmentation.

Adult↗
PubMed1998

Objective specification of tritanopic confusion lines using visual evoked potentials.

The minimum distinct border (MDB) between different isoluminant hues of a bipartite field was set subjectively by adjustment and then according to a 3-point rating allowing determination of the S-cone specific (tritanopic) axis. This rating was compared with visual evoked potentials (VEPs) generated by coarse, isoluminant gratings, modulated along the same chromatic axes. Psychophysically determined tritanopic gratings elicited monophasic onset VEPs with the longest latency for each subject. Departure from this axis produced additional earlier negative components (reflecting additional response mechanisms). Colour-selective VEPs can, therefore, objectively specify tritanopic confusion lines with a comparable degree of accuracy to MDB judgements.

Color Perception↗
PubMed1997

Selective stimulation of colour mechanisms: an empirical perspective.

Anatomically distinct parvo and magno visual pathways show considerable functional overlap. However, specific stimulation of the most sensitive colour-opponent parvo-neurones is still possible, provided that colour stimuli are verified for selectivity. The authors have shown that gratings of low contrast, low spatial frequency and of restricted spatial content (6 or less spatial cycles) are optimal stimuli for distinguishing between colour-related (tritan and red/green) from achromatic or partly chromatic responses. This is particularly important when recording global responses, such as visual evoked potentials, VEPs. The crucial point is that at low presentation rates (< 2 Hz), colour-related onset VEPs are maximally different from contrast reversal VEPs, thereby reflecting the activity of sustained-type parvo mechanisms. Achromatic onset, offset and reversal VEPs are similar, reflecting mediation by transient-type magno mechanisms. A stringent test of colour-response specificity is to check whether the chromatic reversal VEP has a low-pass temporal tuning curve, since it becomes band-pass when substantial achromatic intrusions are present. Specification of chromatic isoluminant stimuli, e.g. along cardinal axes, does not guarantee their colour-selectivity, if chromatic aberration and variable macular pigmentation changes the chromatic content of the retinal image. It is shown here how chromatic stimuli, namely (1) red/green and (2) purple/green (tritanopic) gratings, can be optimized for selective stimulation of the colour system.

Color Perception↗
PubMed1996

Specificity and selectivity of chromatic visual evoked potentials.

A paper by Rabin et al. (1994) Vision Research, 34, 2657-2671, claimed that spatially extensive grating stimuli could be used to generate chromatic-specific visual evoked potentials from subjects assumed to have standard spectral sensitivity and tritanopic confusion lines. Here we demonstrate that such spatially extensive stimuli may generate responses which are contaminated by luminance-contrast intrusions. Such intrusions are mainly due to chromatic aberrations and are compounded by the abovementioned assumptions. Claims regarding the chromatic selectivity of VEPs must, therefore, be substantiated by establishing correlations with the known properties of the chromatic system.

Color Perception↗
PubMed1996

Topical corticosteroids potentiate mucin secretion in the normal nose.

The exact mode of action of topical nasal corticosteroids is still uncertain. The aim of this study was to determine their effects on microvascular permeability and cellular and glandular secretion by measuring the levels of total protein, albumin, lysozyme and mucin recovered in nasal lavage fluid before and after 3 weeks of treatment with a topical nasal corticosteroid in 12 normal non-atopic subjects. Six subjects applied 200 micrograms fluticasone propionate and six applied 200 micrograms beclomethasone dipropionate to one nostril in each 24 h: matched placebo was applied to the other nostril. There was a significant rise in the level of mucin recovered compared with baseline values following fluticasone administration (baseline 76.2 micrograms/ml (mean) +/- 5.5 (SEM), fluticasone 118.3 micrograms/ml +/- 11.6 P = 0.015) and beclomethasone administration (baseline 64.3 micrograms/ml +/- 6.6, beclomethasone 87.2 micrograms/ml +/- 4.8, P = 0.041). There was no significant change in the levels of total protein, albumin or lysozyme following either active medication or placebo treatment. Topical corticosteroids appear to potentiate mucin secretion and do not alter serous secretion or microvascular permeability in the unchallenged non-atopic nose.

Administration, Topical↗
PubMedDate not supplied

Chromatic VEP assessment of human macular pigment: comparison with minimum motion and minimum flicker profiles.

To assess the effects of macular pigment optical density (MPOD) on isoluminant stimuli and to quantify MPOD electrophysiologically, MPOD distribution profiles were obtained in normal subjects using minimum motion and minimum flicker photometry. Isoluminance of VEP stimuli was determined using minimum flicker and tritan confusion lines were determined using a minimum distinct border criterion. Onset-offset and reversal VEPs to isoluminant red/green, blue/green, and subject-specific tritan gratings of different diameters were recorded from the same 14 subjects tested psychophysically. VEPs were additionally recorded to annular gratings. Chromatic VEP selectivity was assessed by Fourier analysis and as an index; onset negativity/(onset negativity + onset positivity). Peak MPOD varied between 0.2-0.8. Chromatic onset VEPs to all isoluminant 3-deg fields were predominantly negative. Larger blue/green and tritan stimuli elicited VEPs with additional positive, achromatic components; for 9-deg gratings, peak MPOD showed negative correlation with the power of the VEP fundamental (r = -0.70) and with the selectivity index (r = -0.83). Annular gratings elicited chromatic-specific B/G VEPs but only when isoluminance was determined for the annulus. Chromatic selectivity loss in VEPs to large B/G or Tritan gratings can be used to estimate subject-specific MPOD. An important implication is that isoluminant Tritan stimuli with short-wavelength components must be restricted in size in order to optimize koniocellular selectivity.

Color↗