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Early perimetrists recognized that the threshold stimulus diameters for visibility and colour recognition differ markedly in peripheral vision. However, we observed that these diameters are identical at the fixation point. This means that these threshold diameters, when plotted against eccentric visual angle, have unequal slopes, perhaps related to recently reported data on estimated magnocellular and parvocellular neural sampling intervals. We therefore collected perimetric data on eleven normal observers, using red stimuli on the Zeiss Jena Type 1 Bowl Perimeter. It was found that the slopes were steeper than those for supposedly corresponding neural data. This could be explained by taking into consideration that (a) the slow rate of stimulus movement allowed parvocellular contribution to visibility; and (b) the possibility of an enhanced foveal representation in the cortical colour processing areas. The clinical significance of these findings is briefly discussed. [ABSTRACT FROM AUTHOR]

The Snellen test has been the most popular clinical measurement of spatial vision for over a century, but it does not fully express the visual ability of an individual. For more analytical purposes the information capacity of the visual system may be assessed by tests of contrast sensitivity and peripheral vision. The visual system selectively reduces the spatial information content of the visual field to avoid overloading the limited capacity for perception and decision making in the brain. The ways in which this reduction occurs and the processing of spatial information is of interest in many disciplines, and theoretical knowledge has been accelerated by the study of artificial intelligence. These processes may be investigated in human subjects by psychophysical and electrophysiological techniques. This provides additional information for diagnostic purposes and will form the basis of new systems of clinical investigation. [ABSTRACT FROM AUTHOR]

An improved method using DTL fibre for electroretinography is described. The DTL fibre is comfortable and easy to apply. Corneal anaesthesia is unnecessary. The DTL fibre does not interfere with the retinal image and has been used successfully to record both pattern and flash electroretinograms from subjects of all ages. [ABSTRACT FROM AUTHOR]

A schematic cortical projection of the human visual field is combined with the concept of dipole planar generators to provide a theoretical model of the scalp distribution of evoked potentials from visual field stimuli. The computations illustrate the importance of gyral surfaces as the principal generators of recorded evoked potentials. Taking several zones of the visual field projection on the striate area as an example, the model is used to produce horizontal profiles of evoked potential amplitude. This indicates the limitation and possibilities of mapping the cortical projections in man and relating these to perimetric findings. [ABSTRACT FROM AUTHOR]

Progress during the last 60 years has revealed numerous electrical signals arising from many parts of the visual system. These now play an essential part in the detection of many pathological conditions. Further progress in the acquisition and interpretation of these signals is necessary however before they could be justified as part of every routine eye examination. Such significant progress is only likely to occur if the electrophysiological origins of each signal can be more precisely identified and understood. Fundamental research on many aspects is therefore necessary. [ABSTRACT FROM AUTHOR]

The British number plate test and the Snellen test of visual acuity are compared. The observations of 60 subjects, 30 of whom have failed the official number plate test, are analysed statistically. It is found possible to estimate the probability of a subject having a specified Snellen acuity, reading a number plate of the 3⅛" (80 mm) symbol type, at 67 ft. (∼ 20.5m). It is considered, however, that the probability of passing the official number plate test is a different value and this is also shown to be estimated from the Snellen visual acuity. The calculations based on the sample of candidates who had failed the number plate test suggest that a driving test candidate with a Snellen decimal acuity of 0.55, or approximately 6/12[SUP+2] in clinical notation, has a 50% chance of passing the number plate test, but the level of visual acuity which would fail the same number of candidates as the number plate test is deduced from an approximate population model, to be 0.6, or 6/9[SUP-2]. Many other quantitative estimates relating the two tests are given in the text and accompanying tables and figures. [ABSTRACT FROM AUTHOR]

Three successive stages in the representations of the visual image are studied by computations from the best available data. The results are embodied in projections, drawn automatically. These projections are related to the assessment of visual disability and the dimensions of lesions in the retina and visual pathway. Fields can be assessed visually with the aid of graticules or directly during computerised perimetry. [ABSTRACT FROM PUBLISHER]