THE EFFECT OF REDUCED VIEWING TIME ON COLOUR VISION IN NORMAL SUBJECTS AND THOSE WITH ABNORMAL OCULAR CONDITIONS

The effect of restricting viewing time to 3.75 ms in normal subjects is to produce a tritan-like colour response on the City University colour vision test. This response pattern is consistent and is repeatable for standard illuminant C at 600 lx. Supplementary tests suggest that the effect is due to a defect of the blue/yellow opponent system rather than a true tritan defect. The same test when repeated on subjects with amblyopia or retinal pathology provides different results which may aid in the differential diagnosis of some visual disorders.     

THE HANDICAP OF ABNORMAL COLOUR VISION

The usefulness of colour coding in industry and the inherited defects of colour vision are briefly reviewed. Operations involving judgment of colour are categorised into four classes: those involving comparative judgment of colour; those involving connotative recognition of colour; those involving denotative recognition and those involving aesthetic judgment. Guidelines for the employment of people with defective colour vision are argued for each category.     

ORIGINS OF COLOUR VISION STANDARDS WITHIN THE TRANSPORT INDUSTRY

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 observers.     

THE EFFECT OF REDUCED VISUAL ACUITY UPON FARNSWORTH 100-HUE TEST PERFORMANCE

Abstract The effect of artificially reduced visual acuity upon performance in the Farnsworth—Munsell 100-hue test has been investigated in a population of 50 individuals with otherwise normal colour vision. Evidence for a significant impairment of performance at low levels of acuity has been obtained.     

EFFECT OF IMPOSED RETINAL IMAGE MOVEMENTS ON COLOUR VISION AT A HETEROCHROMATIC BOUNDARY IN A STABILIZED RETINAL IMAGE

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 ER was 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 than 5'.     

THE EFFECT OF COLOUR OUTPUT OF INTENSIFYING DEVICES ON ACUITY IN PIGMENTARY RETINAL DEGENERATION

Abstract Developments in phosphor technology have resulted in the possibility of producing intensifying devices with a variety of output colours. The present pilot study investigates the effect of phosphor colour on acuity performance in subjects suffering from pigmentary degeneration of the retina. The results of this study combined with previous data on dark adaptation and colour are used to provide recommendations regarding the most suitable intensifier output colour for such subjects.     

AN AVERAGING METHOD FOR THE INTERPRETATION OF THE FARNSWORTH-MUNSELL 100-HUE TEST—I. CONGENITAL COLOUR VISION DEFECTS

A method is described for identifying polarity in Farnsworth-Munsell 100-Hue test data. The method is facilitated by the use of a micro-computer and involves the plotting of "averaged" scores for each cap of the test. Results are presented for 30 protanopes, 30 deuteranopes, 1 tritanope and 2 typical rod monochromats. Analysis of the results shows that the proposed technique is compatible with standard methods of interpreting 100-Hue plots and is suitable to use when error scores are high and when polarity is difficult to interpret.     

THE COMMON VISUAL DISORDERS: THEIR EFFECT ON JOB PERFORMANCE

Common visual disorders are subdivided into two major groups — the ametropias and anomalies of binocular vision. Myopia, hypermetropia and astigmatism are discussed from Sorsby's aetiological standpoint of correlation and component mechanisms, and the incidence of these conditions and presbyopia is detailed with some figures on the necessity for correction. Binocular anomalies of heterophoria, strabismus and amblyopia are described, together with some data on the performance of the one-eyed person. The relationship between visual acuity and illumination is explained with particular reference to the common disorders of vision.     

AN AVERAGING METHOD FOR THE INTERPRETATION OF THE FARNSWORTH-MUNSELL 100-HUE TEST—II. COLOUR VISION DEFECTS ACQUIRED IN DIABETIC RETINOPATHY

The Farnsworth-Munsell 100-Hue test is frequently used to assess acquired colour vision defects. In diabetic retinopathy the acquired defect is a mild or severe type III (Tritan) defect which may be coupled with poor overall hue discrimination. In consequence, error scores are often high and the 100-Hue polar diagram is difficult to interpret. In this study the averaging method of analysis proposed by Dain and Birch is used to examine 120 100-Hue plots obtained by patients with proliferative diabetic retinopathy. These plots have either moderate (150-300) or high error scores (greater than 300). The method of analysis is found to be effective in determining whether a Tritan defect is present or not.