ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00629.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The smallest, continuous target displacement which is sufficient to cause a sensation of movement was measured under conditions of chromatic adaptation. The experiments were carried out for test target and background field wavelengths which selectively isolate the activity of the colour mechanisms of the human eye. The results show that, when target detection is largely mediated by the red or green colour mechanism, a target displacement of 2–3′ in the foveal region is sufficient to cause a reliable sensation of movement. These displacement thresholds show only a small change as a function of target contrast or background retinal illuminance level. Similar results were obtained when the colour of the test target was the same as that of the background field (e.g. green, yellow or red), when no attempt was made to isolate a single colour mechanism. Test target and background wavelengths which isolate the activity of the blue colour mechanism yield displacement thresholds in the range 5–7′ and show a stronger dependence on target contrast and background retinal illuminance level. The experiments were repeated at several eccentricities and the results show that, for a test target and background field of the same colour and under conditions which isolate the green or red spectral response mechanism, the minimum target displacement required for motion detection appears to increase in a manner similar to the centre‐width receptive‐field size of broad‐band, centre‐surround transient neurons in the rhesus monkey retina [De Monasterio and Gouras (1975)J. Physiol., Lond.251, 167–195]. In contrast, displacement thresholds obtained under conditions which isolate the blue colour mechanism do not show significant variation for target presentation locations up to 25° of visual angle. These data relate well to other psychophysical results which reveal the spatial properties of motion‐detecting mechanisms in human vision [Barbur and Ruddock (1980b)Biol.

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00630.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The critical fusion frequency (CFF) was measured across the central visual field. Stimulus parameters were adjusted to ensure an increase in CFF at the fovea. Comparison was made between the foveal and extra‐foveal CFF values. The study showed that, while the CFF may be highest at the fovea when the CFF values are generally low, stimulus parameter changes that increase the CFF result in a greater increase extra‐foveally. Ultimately, then, the CFF maximum shifts from the fovea to an extra‐foveal area. Under the experimental conditions used in the study, the maximum occurred approximately 10° from

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—An objective variation of Howland and Howland's subjective crossed‐cylinder aberroscope method of estimating ocular aberration is described. An ophthalmoscopic arrangement allows the distorted retinal image of the aberroscope grid to be directly photographed for later analysis. Results for 10 subjects show that the ocular wavefront aberration near the visual axis is rarely symmetrical about the pupil centre and that, as a result, the phase transfer function is generally non‐zero. Calculated modulation transfer functions at various pupil diameters broadly agree with those of earlier authors but suggest that marked differences occur between individual eyes when the pupil diameter exceeds about

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00632.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—A split‐laser technique employing red and blue lasers was used for direct measurement of longitudinal chromatic aberration of excised lenses from a spectrum of vertebrates (fish, amphibians, birds and mammals). The chromatic aberration (442–633 nm) of lenses of most species amounts to a relatively constant 4.6% of equivalent focal length. Dog lenses show somewhat larger amounts (5.7%) while duck and rock bass lenses show less wavelength variation in focal length (3.42–2.70%). In general, chromatic aberration varies little with lens eccentricity, although this point requires further study with more attention to paraxial measu

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00633.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Previous investigations have demonstrated an ethanol‐induced increase in distance esophoria and an increase in near exophoria, together with a decrease in negative fusional ability, the AC/A ratio and near point of convergence. The present study (N= 10) was designed to test the hypothesis that these effects are due to a biasing of vergence towards its tonic resting state when under conditions of oculomotor stress. Measurements of the parameters before and 1 hr after imbibition of a moderate dose of ethanol supported the previous findings. Darkroom measures of tonic vergence (vernier alignment) and tonic accommodation (laser optometry) were unaffected by ethanol. The study indicates that the changes in oculomotor function induced by the central inhibitory action of ethanol represent a shift towards the tonic vergence posit

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00634.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—This study compares, under controlled conditions and by rigorous statistical analysis, the contrast sensitivity function (CSF) measured with soft‐lens and spectacle correction, attempting to resolve the conflicting reports in the literature. Ten non‐astigmatic ametropic subjects had the CSF measured at eight spatial frequencies with the two types of visual correction. Analysis of variance revealed statistically significant effects for subjects, stimuli and type of visual correction, statistically superior performance being obtained with soft lenses. However, the actual difference in the CSF for the two forms of correction was small (0.14 log units) and not clinically significant. Comparison of the average CSF for the three highest and lowest spatial frequencies tested revealed a significant advantage in using higher spatial frequencies in the determination of statistical differences in the CSF obtained with different types of visual corre

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00635.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Fresnel prisms placed on the spectacle lenses of a patient with optic atrophy resulting from an accident eliminated constant diplopia in the remaining visual field. A reduction in vision due to Fresnel prisms was found to be more tolerable than diplopi

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00636.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—As conventionally recorded, visual acuity data constitute an ordinal scale of measurement. An investigation of four different clinical samples shows that visual acuity is not normally distributed amongst these populations. Furthermore, acuity is often measured on charts which, by the inherent restriction of the stimulus size, have the effect of truncating the upper limit of the scale producing, in statistical terms, an incomplete distribution. The distribution of acuity for each sample is found to be adequately described in terms of the equation:F(x) =Axα(T‐x)β, whereF(x) is the cumulative distribution of the statistical population,Tis the truncation level (known),xis the Snellen decimal acuity (known) andA, α and β are parameters. Alternative analytical procedures based upon this model, which overcome these limitations, are di

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00637.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Initial results are reported of a major study undertaken to determine factors which could be used to predict employment success of partially‐sighted school leavers. The sample involved 355 individuals from 13 schools for the partially sighted taken from three successive final academic years and followed up 1 year after leaving school. Questionnaire techniques were used, the response rate being 85.6%. Analysis revealed that 55.6% sought or experienced employment and 44.4% undertook further education. Eighty‐seven per cent of those seeking employment obtained jobs alongside the normally sighted. Only 12 leavers remained totally unemployed. Forty‐seven per cent were still in their initial emp

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1985.tb00638.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY