ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01154.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Colour vision standards should reflect changes in our understanding of the nature of these defects as well as technological advances that place less importance upon the visual senses of the human operator. Therefore it is suggested that visual standards be subject to routine reviews in order to assess their suitability for modern. work environments. This paper gives a chronological account of the introduction of colour vision standards by several national transport authorities and identifies historical reasons that led to their implementation. It is concluded that the same factors that gave rise to the adoption of early colour vision standards are still relevant for modern transport systems. However the recent deployment of automatic or semi‐automatic control or navigational systems has substantially altered man's role from being the primary source of information input to one of a monitoring process. This has generated a good deal of debate and uncertainty regarding the level of responsibility that a human operator has for the control of modern transport vehicles. Nevertheless, it is argued that in the absence of complete automation some type of visual standard is needed whenever visual judgements must be made by human observ

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01155.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—A stabilized image, including a straight‐line boundary between two areas of different colour was displayed. Movements normal to itself were imposed on this boundary while other boundaries remained stabilized. Broad band filters giving red, yellow, green and blue were used in various pairs. Step movements, pulse movements and oscillatory movements (including sinusoidal, triangular and square wave forms) were applied in turn. Threshold movements to give perception of hue were measured for steps and pulses and signal/photon‐noise ratios were calculated for a red/blue boundary. The ratio was found to be constant at a value of about 20 when the retinal illuminance (ER) varied between 5 td and 60 td. When ERwas increased (up to 2000 td) the ratio increased rapidly. None of the colour appearances produced by moving the boundary exactly matched the corresponding appearances in an unstabilized image, though the nearest matches were obtained with oscillatory movements of frequency 2 Hz and displacement greater t

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01156.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Two sample groups of domestic cats were assessed for (a) central corneal thickness (17 eyes), using optical pachymetry, and (b) horizontal and vertical corneal diameter, using a photographic method (20 eyes). The average corneal thickness was 0.755 _+ 0.33 mm. The mean horizontal diameter was 16.5 ‐/+ 0.60 mm and the mean vertical diameter was 16.2 2‐/+ 0.61 mm. The horizontal corneal diameter was significantly greater than the vertical corneal diameter (p<0.001, paired t

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01157.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—In previous studies the ability of the oculomotor system to adapt to prism‐induced heterophoria has been shown. The phoria that occurs immediately after a prism has been placed before one eye gradually reduces and returns to its original baseline value as the subject is allowed binocular experience while wearing the prism. Little work has been carried out to determine when the adaptation is complete. In this study we report on the results of two experiments designed to determine when adaptation is complete. In the first, the rate of decay of adaptation, i.e. loss of slow fusional vergence, is measured after varying periods of forced vergence. In the second experiment the rate of adaptation to an additional disparity is measured: this should be the same as that before the induced effect if adaptation is complete. The results of this study indicate that although adaptation may appear complete by the criterion that the phoria has returned to its baseline value, the adaptation is unlikely to be truly complete for a much longer period of time has pas

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01158.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—A new fixation disparity measuring device, the Wesson Fixation Disparity Card, is compared with the modified Sheedy Disparometer. Twenty‐eight subjects were divided into normal and abnormal categories of binocular status determined by clascical clinical techniques rather than on patients' subjective symptomatology. Fixation disparity curves were generated on all subjects using both instruments. There were significant differences between the two instruments. Neither instrument was able to distinguish between normal and abnormal subjects but, over a five day period, each instrument produced repeatable results. The validity of fixation disparity measurements using either instrument on naive observers, especially children, is questio

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01159.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Some stimuli, if scaled in proportion to the reciprocal of inter ganglion cell receptive field separation (M‐scaled) exhibit an isosensitivity profile. Perimetric profiles which are isosensitive across the extent of the normal visual field facilitate multiple stimulus perimetry and provide a convenient method for the detection of abnormality. The purpose of the investigation was to establish whether the stimulus diameters necessary to produce an isosensitive perimetric profile were scaled in proportion to M. Sensitivity profiles for a sample of 15 age‐matched observers were obtained with the Friedmann VFA Mk II. The stimulus aperture diameters were then measured under 100 x magnification. The observed elliptical apertures, corrected for obliquity of viewing, plate thickness and distance from the eye were represented as diameters of circles possessing an equivalent area to that of the ellipse. The apparent diameters were then M‐scaled relative to stimulus pattern h using the equations of Rovamo and Virsu (1979). An overestimation of the M‐scaled diameters relative to the apparent diameters was noted which increased with eccentricity for all four cardinal meridians by a factor of up to 3.5 times. It is suggested that the over compensation indicates that the cortical representation of perimetric spot targets at low photopic adaptation levels depends not only upon retinal ganglion cell density but also upon the variation of ganglion cell characteristics with eccentricity. The implications of this finding for perimetric instrument design are

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01160.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—A new photographic‐based system has been developed for the measurement of contrast sensitivity in human vision. The system has several advantages over other photographic methods and is relatively easy and inexpensive to produce. This paper describes the design of the new system and the methods used in the production of the photographic prints. Preliminary tests show that full contrast sensitivity curves can be obtained with a small number of photographic prints and that these curves are very similar to those obtained using a carefully calibrated electronic pattern genera

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01161.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—Fresnel prisms are often used in orthoptics for binocular anomalies and in low vision for visual field defects. These prisms are made of optical polyvinyl chloride (PVC) and this material increases chromatic dispersion and produces a loss of contrast. In this study, the effect of chromatic dispersion on contrast sensitivity is determined. Contrast thresholds over a wide range of spatial frequencies are obtained on a number of subjects with the use of Fresnel prisms ranging from 5 to 30 prism dioptres. As predicted there is a decrease in visual acuity and cut‐off spatial frequency threshold as prism power increases. Similarly, a decrease in contrast sensitivity at high and medium spatial frequencies is recor

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01162.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract—A paraxial computing scheme is described for tracing an axial pencil of rays through any system containing astigmatic surfaces with their axes at random. In conjunction with a scheme for tracing oblique rays (Bennett, 1986) it is applied to a problem in visual optics posed by Keating (1982). This involves determining the spectacle magnification for a schematic eye with three strongly astigmatic surfaces, corrected by a spectacle lens of bi‐toroidal form, the axes of all five surfaces being mutually oblique. It is shown that the suggested computing schemes yield very similar results to those found by the matrix methods of Keating. Although only two rays are needed to determine the principal dimensions of the basic retinal image of a circle, further insight into its true shape is obtained from a multiple trace, using a computerized version of the ray tracing sch

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1986.tb01163.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY