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D Keating

Publications and source records attributed to D Keating.

At least 19 recordsLinked to original sources
PubMed2005

Retinal toxicity during pegylated alpha-interferon therapy for chronic hepatitis C: a multifocal electroretinogram investigation.

BACKGROUND: Ocular side-effects in the form of retinal ischaemia and haemorrhages have been reported in patients undergoing standard alpha-interferon therapy. AIM: To assess the ocular impact of therapy with sustained release pegylated alpha-2a interferon (Pegasys) for chronic hepatitis C. METHODS: Ten patients receiving Pegasys and ribavirin and 10 healthy volunteers were recruited. Patients underwent full ophthalmic investigations and multifocal electroretinogram testing at baseline, at regular intervals during treatment and post-treatment. The multifocal electroretinogram maps retinal function. Responses were compared with sequential recordings from healthy volunteers. RESULTS: All patients had normal clinical ophthalmic investigations at baseline. During therapy a single patient experienced central visual disturbance lasting 24 h with no prolonged ill effect. No other patient was aware of any change in vision. Fundal abnormalities appeared in five patients during treatment. The multifocal electroretinogram showed reductions in retinal function in five patients. Nine of 10 patients exhibited abnormalities on at least one multifocal electroretinogram or fundoscopic investigation. CONCLUSIONS: Subclinical retinal toxicity during anti-viral therapy with pegylated alpha-interferon and ribavirin was frequent in this study and it suggests that patients should be warned of this risk and monitored during therapy.

Adult↗
PubMed2004

The effects of pupil size on the multifocal electroretinogram.

This is an investigation of the effect of changing the pupil diameter on the P1 amplitude and latency of the multifocal electroretinogram (mfERG). MfERGs were recorded using a custom built wide field electrophysiological system. An array of 61 empirically scaled hexagons was used to stimulate the visual field. The duration of overall recording period was 8 min, segmented into 16 intervals each lasting 30 s. A combination of mydriatics and miotics were used to pharmacologically alter the pupil size and diameters between 1 and 10 mm were measured. There was a reduction in mfERG P1 amplitude in some cases greater than 50% (mfERG P1 amplitude 53 nV at 8 mm to 25 nV at 1 mm), with a change in pupil diameter of 7 mm. The mfERG P1 latency increased in some cases by as much as 8 ms in the central 40 degrees (mfERG P1 latency 39 ms at 8 mm to 47 ms at 1 mm). These results suggest that pupil size has significant effects on mfERG P1 amplitude and latency.

Electroretinography↗
PubMed2004

Secondary retinal changes associated with choroidal naevi and melanomas documented by optical coherence tomography.

AIMS: To establish the characteristics of secondary retinal changes associated with the presence of choroidal melanomas and choroidal naevi as documented by optical coherence tomography (OCT). METHODS: Twenty patients with untreated choroidal melanoma and 40 patients with presumed choroidal naevi managed by regular observation were included in the study. OCT scans across the surface of the tumour and surrounding tissue were acquired for all participants. The appearance of retinal tissue on the OCT scans was considered to be abnormal if it did not display the well defined band structure characteristic of normal tissue on OCT scans. RESULTS: Serous retinal detachments were observed in all patients with choroidal melanoma and 18 out of 20 also had abnormal retinal structure or intra-retinal splitting in the tissue overlying the tumour. Out of the 40 patients with presumed choroidal naevi, 12 had serous detachments and three had either abnormal retinal structure or intra-retinal splitting overlying the lesion. CONCLUSIONS: Secondary retinal changes associated with choroidal lesions can be documented by OCT. These changes were observed in most patients with choroidal melanoma included in the study group but were far less prevalent in the patients with presumed choroidal naevi. OCT is also able to identify the presence of small serous detachments before they become clinically visible. Follow up of these patients is required to determine whether the OCT results may be of use in the differential diagnosis of small choroidal lesions.

Adult↗
PubMed2003

Peripheral retinal dysfunction in patients taking vigabatrin.

OBJECTIVE: To assess the wide-field multifocal electroretinogram (WF-mfERG) for assessment of retinal function in vigabatrin-treated patients. METHODS: Thirty-two adults who had taken vigabatrin for at least 3 years for localization-related epilepsy underwent WF-mfERG, ERG, logMar visual acuity and color vision evaluation, Humphrey visual field analysis (static perimetry), and funduscopy. The group was matched with a cohort of patients who had never received vigabatrin. Results were compared with a normative data set (120 drug-free controls) with respect to potential bilateral abnormalities in response timing. RESULTS: There were no significant differences between groups in visual acuity or color vision testing. Of the vigabatrin patients, 19 (59%) had bilateral visual field defects compared to none of the controls. Using WF-mfERG, all patients on vigabatrin with visual field defects showed abnormalities (100% sensitivity) and only 2 of the 13 patients without a field defect showed retinal abnormalities (86% specificity). CONCLUSIONS: WF-mfERG may be useful for detecting retinal pathology in patients taking vigabatrin. The majority of previous reports based on subjective testing may have underestimated the prevalence of peripheral retinal toxicity related to the drug.

Adult↗
PubMed2002

Identification of appropriate primitive polynomials to avoid cross-contamination in multifocal electroretinogram responses.

Abstract-The basis of the multifocal/electroretinogram is the use of a decimated m-sequence for simultaneous and independent stimulation of many areas of the visual pathway. The purpose of this study was to investigate the effects of cross-contamination from higher orders of the response. A series of primitive polynomials were found by construction of finite fields. The first-order ERG response was formed by cross-correlation of m-sequence with the physiological response. A second-order response was formed by investigation of particular flash sequences of the stimulation sequence and cross-correlation of a second-order m-sequence with the physiological response. Zech logarithms were used to identify cross-contamination between the various first and second-order sequences. Tables of good and bad primitive polynomials were constructed for degrees 12-16, and the effects of window length and decimation length were examined. When the sequence was decimated into 128 areas, and a window of length 16 was examined, cross-contamination occurred in all sequences generated from primitive polynomials of degree less than or equal to 12, but in only 26% of degree 14, and 5.6% of degree 16. A photodiode (artificial eye) was used in an experiment to construct trace arrays showing responses from 61 individual areas. Additional waveforms were present on the trace array when the experiment was carried out with a bad primitive polynomial. The use of finite field theory to generate primitive polynomials and Zech logarithm analysis allowed prediction of which primitive polynomials were suitable for m-sequence generation for multifocal electroretinography. Practical investigations supported the theoretical analysis. This has important implications for developers of multifocal electrophysiology systems.

Artifacts↗
PubMed2001

A comparison of CRT and digital stimulus delivery methods in the multifocal ERG.

The purpose of this paper is to compare and evaluate the multifocal ERG response from raster based CRT and Digital Projection (LCD) stimulus delivery systems. A custom built p.c. based multifocal system was used to generate a 61 hexagonal element stimulus array. The stimulus was presented on a high luminance CRT display and on a back projected screen using a Digital polysilicon projection system. A fast response photodiode was used to analyse the stimulus pulse characteristics of both systems. A number of recordings were performed to assess the effect of stimulus delivery on a standard m-sequence response, inserted full-field filler response and on separation of onset and offset components. The pulse width for a CRT system is dependant on the type of phosphor and is typically 2 msec whereas the Digital Projection system produces a 13.3 msec pulse equivalent to the frame rate for the system. Slowing down the m-sequence by a factor of eight results in a pulse width of 106 msec which should enable the recovery of true offset responses. The CRT stimulus consists of a series of eight pulses of 2 msec duration each separated by 11.3 msec. First order responses are larger from the CRT system and second order responses larger from the Digital system. In conclusion, there are fundamental differences in the two delivery systems. The CRT system may have more potential in examining non-linear aspects of the multifocal response. Although both systems may be able to record offset responses, the Digital system will generate true offset responses whereas the CRT system may not allow true separation of these components.

Adult↗
PubMed2001

The impact of fixation on the multifocal electroretinogram.

There are a number of variables which can influence the quality of multifocal ERG waveforms. In common with visual field measurements, fixation quality may be an important parameter on the integrity of the acquired data. A low cost, fixation-monitoring device was used to assess fixation quality on a group of normal volunteers. Data was successfully acquired while five subjects viewed a fixation target for a period of time equal to that of a single multifocal recording segment. The target was presented on a stationary grey background and as the central fixation mark on a 61-element multifocal flicker stimulus. The results show no significant difference with or without the flickering pattern. The percentage of samples falling within 1.2 degrees of the point of fixation was 51%. This suggests that fixation quality is adequate for scaled stimuli where the central element subtends 2.4 degrees. High resolution stimuli of less than 2.4 degrees may be more susceptible to fixation fluctuations during the recording process.

Adult↗
PubMed2001

Childhood speech disorders: reported prevalence, comorbidity and socioeconomic profile.

OBJECTIVE: To describe the reported prevalence, comorbidity and socioeconomic status (SES) of children with speech disorders. METHODOLOGY: Data from the 1995 Australian Health Survey were used. Information relating to the health of 12 388 children aged 0-14 years was collected via face-to-face interviews with a responsible adult. Speech disorders were recorded if children had reported difficulty talking, producing speech sounds, or who stuttered. RESULTS: The prevalence of childhood speech disorders (CSD) was 1.7% (n = 209). Of this group, 25.8% (n = 54) had a developmental delay or intellectual impairment; when these were excluded, the prevalence of CSD was reduced to 1.3% (n = 155). Among males, the peak prevalence occurred at age 5 (6.5%), for females the highest rates were for 3-4-year-olds (1.8%). Children with a speech disorder had a greater number of additional health problems. No relationship was found between SES and CSD. CONCLUSIONS: Children with speech disorders often have complex health and developmental needs. Developing effective prevention programs with a view to improving the long-term health and social outcomes of these children will require a mix of individual (clinical) and population-based (public-health) strategies.

Adolescent↗
PubMed2000

Technical aspects of multifocal ERG recording.

There are a wide range of variables which can influence the quality of the multifocal response. It is possible to place these variables into one of four categories. First, the method of stimulus delivery will determine the field of view, interference levels and the duration of on-state stimulation. Second, data acquisition variables such as electrode type and placement, amplifier specifications and filter bandwidth settings will have a direct impact on waveform shape and on the topographic distribution of signal amplitudes. Third, patient variables such as fixation, pupil dilation and refractive error will also contribute to the multifocal response. Fourth, there are many measurements that can be taken from multifocal recordings. In addition to standard amplitude and implicit time measures (the implicit time measure in the multifocal response is becoming increasingly important particularly in early stages of disease processes), the scalar product measure provides information on waveform shape. The conventional impulse and higher order responses will be different for different modes of stimulation such as Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD) systems and latency shifts will be introduced if not corrected in software. Procedures which could lead to misleading interpretation include artefact rejection, averaging with neighbours and summing of responses. These procedures should be handled with caution.

Electroretinography↗
PubMed2000

Letters to the editor

The placement of MRSA carriers in private nursing homes: does information influence acceptance? Copyright 2000 The Hospital Infection Society.

Journal Article↗
PubMed1999

Three-dimensional electromagnetic model of the human eye: advances towards the optimisation of electroretinographic signal detection.

Classical electromagnetic theory is used to examine the topographical variation in electrical potentials over the corneal surface resulting from specific retinal stimuli. Results from a three-dimensional mathematical model show that over 97% of calculated electromagnetic field potentials lie within 3% of previous analytical model data for an axially symmetric case. Maps of corneal potentials are produced that are shown to be characteristic of specific retinal stimuli and location. The maximum variation in corneal potential for a full field global stimulus is found to be approximately 1%. This is considered encouraging, as current electrophysiology techniques measure ocular potentials from a single corneal or scleral site, the position of which is often difficult to localise and reproduce. The model is used to simulate both central and peripheral stimuli and scotoma conditions. A 20 degrees central scotoma simulation shows an overall reduction in central corneal potential of only 3%, whereas peripheral stimuli are found to cause up to 10% variations in this potential. There is therefore a possibility that a single recording site for multifocal retinal stimulation is not ideal. These data may be used to suggest more appropriate electrode recording positions for maximum signal recovery, not least in optimising signal detection for multi-focal electroretinography stimulation.

Electromagnetic Fields↗
PubMed1999

Ability of mammography to reveal nonpalpable breast cancer in women with palpable breast masses.

OBJECTIVE: Our goal was to determine the frequency with which mammography reveals nonpalpable malignancies in women with benign palpable masses and to compare these nonpalpable malignancies with the palpable malignancies and nonpalpable malignancies detected in asymptomatic women. SUBJECTS AND METHODS: This study of nominally asymptomatic women involved 85,399 consecutive mammographic examinations, of which 3459 (4.1%) examinations were performed on women who had palpable masses identified before or at the time of mammography. A medical outcomes audit identified mammographic examinations after which breast cancer was diagnosed and determined selected surrogate measures for mortality reduction for the mammographically detected malignancies. RESULTS: Of the 3459 examinations in women with palpable masses, 64 cases of cancer were revealed by mammography. Of these, 54 cases involved palpable malignancies (15.6/1000 examinations) and 10 involved nonpalpable malignancies (2.6/1000 examinations). Of the 81,940 examinations in asymptomatic women, 346 cases of nonpalpable cancer were detected (4.2/1000 examinations). Of the 10 cases of nonpalpable cancer detected in women with benign palpable masses, median tumor size was 13.8 mm, 10% had axillary node metastasis, and 10% were stage 2 or higher. The corresponding surrogate measures for cases of nonpalpable cancer detected in asymptomatic women were median tumor size, 13.6 mm; node metastasis, 7%; stage 2 or higher, 14%. The surrogate measures for the 54 palpable malignancies were median tumor size, 23.7 mm; node metastasis, 31%; stage 2 or higher, 63%. CONCLUSION: The surrogate measures for the nonpalpable malignancies in women with benign palpable lesions resemble those in asymptomatic women and are much more favorable than those of palpable malignancies. Therefore, in women with a palpable breast mass, it is important to use mammography to screen the remainder of both breasts for nonpalpable cancer.

Adult↗