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S J Crews

Publications and source records attributed to S J Crews.

At least 19 recordsLinked to original sources
PubMed1996

ERG and EOG abnormalities in carriers of X-linked retinitis pigmentosa.

The diagnosis of X-linked retinitis pigmentosa (XL-RP) relies on the identification of the female carriers, in whom fundal abnormalities are often minimal and variable. The electroretinogram (ERG) has been reported as abnormal in 54-96% of heterozygote females. This study examines the combined use of electro-oculogram (EOG) and standardised ERG in 31 obligate and 33 non-obligate carriers of XL-RP. In the obligate carrier group, the EOG was abnormal in 13 carriers (41%), the ERG abnormal in 21 carriers (68%) and a combined EOG and ERG abnormality occurred in 24 carriers (77%). An EOG abnormality alone occurred in 2 carriers (6.5%). Fourteen obligate carriers (45%) showed a peak to peak delay of the ERG scotopic b wave, this being a previously unreported phenomenon. Similarly, in the non-obligate carrier group, the EOG was abnormal in 11 carriers (44%) and the ERG abnormal in 19 carriers (73%). The results of this study suggest that the use of both tests, including measurement of the scotopic b wave latency, may increase the carrier detection rate.

Adolescent↗
PubMed1990

The influence of forward light scatter on the visual field indices in glaucoma.

Light scatter was induced in 15 glaucoma patients, exhibiting clear media and moderate field loss, using cells containing varying concentrations of 0.5 microns diameter latex beads in distilled water. The right eye was examined with program G1 on the Octopus 201, and with a 45 degrees threshold profile on the Dicon AP3000, with and without a given cell. Forward light scatter due to the cell was assessed by measuring the depression of contrast sensitivity, with the Nicolet CS2000, under glare conditions. Perimetric mean sensitivity decreased linearly and loss variance decreased curvilinearly with increase in forward scatter. Threshold values for 26 glaucoma patients, determined in the absence of induced scatter, were then corrected for the effects of naturally occurring intraocular light scatter. The recalculated mean defect decreased linearly while loss variance remained essentially unchanged. Forward light scatter therefore predominantly exaggerates diffuse loss; the apparent underestimation of focal defects caused by induced scatter is partly a computational artefact resulting from inapplicable age-matched normal reference data.

Aged↗
PubMed1989

Alterations in the shape of the automated perimetric profile arising from cataract.

The attenuation of the perimetric response arising from cataract was investigated and related to the degree of cataract quantified by glare sensitivity. Visual fields were measured with the Octopus and Dicon automated perimeters out to an eccentricity of 30 degrees. Nuclear and non-nuclear cataracts differed in their effect on the perimetric profile. Non-nuclear cataracts exhibited the same qualitative characteristics as a model developed in previous studies, whereby the overall pattern of perimetric attenuation was dependent upon target configuration. For these subjects, perimetric sensitivity was depressed to a greater extent at an eccentricity of 30 degrees compared with fixation when measured with the large projected stimuli, whereas the reverse was true when sensitivity was measured with the small LED stimuli. Conversely, nuclear cataracts depressed perimetric sensitivity to a greater extent at the fovea compared with more peripheral regions for both the large projected and small LED stimuli.

Aged↗
PubMed1989

The influence of the learning effect on automated perimetry in patients with suspected glaucoma.

The influence of the learning effect on the outcome of automated perimetry was studied as a function of eccentricity. The same comprised 20 patients with suspected glaucoma who were all naive to automated perimetry. Visual field examination of the right eye followed by that of the left eye was undertaken on each of three successive days and after a further interval of 12 days using a customized full-field program of the Humphrey Field Analyser 630 (stimulus size III). The program comprised 60 points out to an eccentricity of 60 degrees with an interstimulus grid of 12 degrees. Global, central, peripheral, superior and inferior mean sensitivity each significantly increased (P less than or equal to 0.01) from the first to the second right eye examinations and from the third to the fourth left eye examinations (P less than or equal to 0.01). The global short-term fluctuation, central mean defect and number of stimulus presentations decreased from the first to the second right eye examination (P 0.01). The order of examination between eyes and the interval between examination sessions influences the response recorded by automated perimetry.

Clinical Competence↗
PubMed1989

Value of the ERG in congenital nystagmus.

A group of 64 children with poor vision and early onset nystagmus were investigated retrospectively by the electroretinogram (ERG). Fifty-eight of these children also underwent analysis of the visual evoked potential (VEP), and 40 underwent colour vision analysis. Seventeen children were found to have complete congenital achromatopsia (rod monochromatism), being identified by their total colour blindness, reduced visual acuity, and reduced or absent photopic and flicker (30 Hz) ERGs. Two children with incomplete X-linked congenital achromatopsia were also found. This study identified the need to investigate children with nystagmus by means of the ERG and suggested that the ERG was useful where the diagnosis was uncertain, particularly at early school age. The incidence of congenital achromatopsia in a group of otherwise undiagnosed children with early onset nystagmus was high (29%), with 40% being classified as having congenital idiopathic nystagmus.

Adolescent↗
PubMed1989

Ten years experience of a genetic eye clinic: 1978-1987.

Over a ten year period of running a joint ophthalmological/genetic clinic, 387 index patients were advised, and a further 260 individuals (relatives of the above) were examined and counselled. Determination of the precise diagnoses and modes of inheritance in the index patients necessitated retinal function tests in 267 (69%) and examination of 84 of their parents and 23 sisters and daughters. Finally, 41% of index patients and 39% of their relatives were given high risks for transmitting an autosomal dominant or X-linked disorder to their children. It is noteworthy that 16% of these high-risk index patients and 66% of these high-risk relatives had no visual symptoms; ophthalmological expertise was required to assess the significance of their minor signs. It was concluded that an active Register is required for contacting relatives outside the nuclear family, and for future recall of children currently too young for carrier tests or genetic counselling.

England↗
PubMed1988

Peripheral refractive correction and automated perimetric profiles.

The effect of peripheral refractive error correction on the automated perimetric sensitivity profile was investigated on a sample of 10 clinically normal, experienced observers. Peripheral refractive error was determined at eccentricities of 0 degree, 20 degrees and 40 degrees along the temporal meridian of the right eye using the Canon Autoref R-1, an infra-red automated refractor, under the parametric conditions of the Octopus automated perimeter. Perimetric sensitivity was then undertaken at these eccentricities (stimulus sizes 0 and III) with and without the appropriate peripheral refractive correction using the Octopus 201 automated perimeter. Within the measurement limits of the experimental procedures employed, perimetric sensitivity was not influenced by peripheral refractive correction.

Adult↗
PubMed1987

Some concepts on the use of three-dimensional isometric plots for the representation of differential sensitivity.

An increasing use is being made of three-dimensional isometric plotting to represent the topography of the visual field. The format of such plots, however, can be manipulated depending upon the parameters of the plotting routine. Problems associated with generating these plots such as resolution of the plotting grid, scaling of sensitivity and orientation of the plot are discussed with reference to both normal and abnormal fields derived by the Octopus 201 automated perimeter (stimulus size III). Recommendations for this type of perimetric representation are suggested.

Diagnosis, Computer-Assisted↗
PubMed1987

Induced intraocular light scatter and the sensitivity gradient of the normal visual field.

The influence of intraocular light scatter on the perimetric sensitivity profile of the normal eye was investigated using a series of light-scattering cells containing 0.01%, 0.02% and 0.025% concentrations of 500 nm diameter latex beads. The degree of induced intraocular light scatter was quantified by measuring contrast sensitivity using the Nicolet CS2000 system in the presence and absence of both wide- and narrow-angle glare light. Perimetric sensitivity out to an eccentricity of 30 degrees was assessed, using the Octopus 201 and the Dicon AP3000 automated perimeters, with the three light-scatter cells and in the cell-free control condition. The results for both functions were expressed as the difference between the control response and that recorded under the particular experimental condition. Perimetric attenuation increased with increase in intraocular light scatter; the extent of the attenuation varied with stimulus type, bowl luminance and eccentricity.

Adult↗
PubMed1987

Serial examination of the normal visual field using Octopus automated projection perimetry. Evidence for a learning effect.

The influence of prior perimetric experience on the magnitude of both differential sensitivity and the short and long term fluctuations remains unclear, and confounds accurate interpretation of visual field data obtained by computer-assisted perimetry. The purpose of the experiment was to identify and quantify any influence of training on the automated perimetric response. The full field of the right eye of 10 clinically normal, naive subjects was examined on 8 occasions with Octopus Program 21 (target size 3) on days 1-5 inclusive, 15, 16 and 44. Sensitivity increased with serial examination in 8 subjects. By dividing the field into zones, it was demonstrated that the learning effect was greatest in the superior field and for eccentricities beyond 30 degrees.

Adult↗
PubMed1986

Stimulus investigative range in the perimetry of retinitis pigmentosa: some preliminary findings.

The manipulation of perimetric stimulus parameters over a given dynamic range has been reported to provide diagnostic information additional to that of changes in differential sensitivity. Preliminary studies (Flanagan et al., 1984a) have indicated that the perimetric response in retinitis pigmentosa behaves atypically over a range of stimulus combinations and strategies. The current study investigated the perimetric response of 17 retinitis pigmentosa patients of various genetic types over a range of stimulus parameters (target size, presentation time and background luminance) and test strategies (kinetic and threshold static) using the Octopus automated perimeter, the Goldmann and Tubinger bowl perimeters and the Dicon Autoperimeter 3000. Statokinetic dissociation was found to be present with large target sizes at 10 asb and 31.5 asb bowl luminances. Some patients demonstrated enhanced sensitivity to shorter stimulus presentations.

Adult↗
PubMed1986

The interpretation of the differential threshold in the central visual field.

Computer assisted perimetry has revolutionised the investigation of the visual field. Experience of central field assessment with the Octopus Automated Perimeter shows that sensitivity recorded with target size 3 across all age groups can frequently be greater than the published normative values. Use of the latter values can therefore provide a serious underestimation of field loss. Inter-individual variation in sensitivity is found within and between age groups. The limitations associated with the use of the measurement error to define abnormality and the additional problems of hypernormal thresholds and resolution of the blind spot are discussed. It is suggested that methods should be developed to evaluate sensitivity on an intra-individual basis.

Adolescent↗
PubMed1986

Perimetric profiles and cortical representation.

The nature of the interaction between spatial summation and M-scaling was investigated by means of the Octopus automated perimeter. It was found that M-scaling of spatial stimulus parameters, alone, did not result in the expected isosensitivity profile. A clinically flat profile was, however, obtained within the central 30 degrees along the horizontal meridian using a large uniform size target (size 3; projected diameter 0.431 degrees). The eccentricities at which presentation of the standard Goldmann targets would result in an isosensitivity profile across the full extent of the visual field were calculated to further illustrate the over-compensation inherent in the current M-scaling equations.

Adult↗
PubMed1985

Manipulation of sensitivity in visual field investigation.

Sophistication of computer software and flexibility of stimulus and background luminance parameters in static perimeter design offer the opportunity for increased information in the assessment of the visual field. Relationships between dynamic ranges and resulting sensitivity gradients in a group of 10 normal 21 year old subjects using the Octopus automated perimeter, the Dicon Autoperimeter 2000 and the Friedmann VFA II are assessed. Inadequacies in the use of normative data to assess the visual field are noted. Implications for the use of dynamic range/sensitivity gradient relationships in visual field assessment without reliance on normative data are discussed.

Adult↗
PubMed1985

Retinal detachment in retinitis pigmentosa.

Three cases of retinal detachment occurring in patients with retinitis pigmentosa are presented and three previously reported cases reviewed. All the detachments were rhegmatogenous. One patient had a horseshoe tear, one had oral bay tears, two had dialyses, one a giant tear and in one case the break was not specified. Three patients were high myopes. All the patients were young males. The five operable cases all responded satisfactorily to conventional surgery. Histologically apparent adhesions between retinal pigment epithelium and neuroretina have been described in advanced cases of retinitis pigmentosa in older patients and may not be present in younger patients with less advanced disease. Until these adhesions occur patients with retinitis pigmentosa may have no additional protection against retinal detachment.

Adolescent↗
PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: I. Scoring system.

Previous methods for the qualitative evaluation of visual field instruments are subject to certain limitations. A system is proposed to overcome these deficiencies. It has been developed from experiences of a clinical study involving 5 different visual field instruments. The method uses 4 levels of analysis and permits separate appraisals of diagnostic potential and detailed inter-instrument comparative evaluation.

Computers↗