Multi-flash campimetry as an indicator of visual field loss in glaucoma.

Multi-flash campimetry is a computer-implemented technique used for the rapid assessment of temporal resolving power across the visual field. On the basis of previous reports that glaucoma patients exhibit impaired temporal sensitivity earlier than conventional perimetric field loss, the question of whether multi-flash campimetry might also be sensitive to the visual consequences of glaucoma was explored. Of the 27 patients that were tested, only one had normal temporal resolving power in both eyes, suggesting that multi-flash campimetry might be a useful aid in determining whether a patient should be diagnosed and treated as a glaucoma suspect or as a confirmed glaucoma patient.

Evaluating visual loss with multi-flash campimetry.

Multi-flash campimetry is a computer-implemented psychophysical technique that allows temporal resolution to be assessed in 120 points per eye in a half hour. It has previously been reported that the results can serve to distinguish between multiple sclerosis patients and control subjects. We have now used this technique to measure temporal resolution in patients with amblyopia, cataracts, optic neuritis or macular degeneration. Our results indicate that multi-flash campimetry is at least as sensitive to visual loss in patients with amblyopia or cataracts as visual acuity testing with the Snellen chart and kinetic visual field testing with the Goldmann perimeter. Further, multi-flash campimetry may be more sensitive than the other two techniques to subtle residual loss in patients who have had optic neuritis and to early loss in patients with macular degeneration.

Monitoring demyelination in multiple sclerosis with multi-flash campimetry.

Multi-flash campimetry is a computer-implemented psychophysical technique that allows a rapid and extensive assessment of visual flicker sensitivity. Multi-flash field maps generated from the data typically reveal the presence of 'islands' of degraded temporal resolution in multiple sclerosis (MS) patients, but not in normal control observers. These distinct 'islands' presumably reflect the influence of demyelination as well as a variety of other possible transient factors, such as edema and inflammation of the optic nerve. The question addressed in the present study concerned a means of distinguishing among such influences. The strategy employed was to test MS patients more than once over a period of several months. Under the assumption that there is little or no significant remyelination in the central nervous system, it was argued that 'islands' that remain present over time should be those that principally reflect demyelination. Transient changes that appear in the fields of MS patients probably reflect the influence of other mediating factors. Examples of multi-flash field maps are presented to illustrate this point and to serve as an initial assessment of the reliability of the technique. It is concluded that multi-flash campimetry may prove to be an effective aid in documenting the degree of progressive visual involvement in MS, and provide a means of monitoring the clinical course of demyelination in the visual system.

An anticipated threshold technique for measuring contrast sensitivity.

A new psychophysical procedure for assessing contrast sensitivity rapidly and reliably is reported. The technique consists of increasing the contrast of a conventional sine wave grating according to the parameters set in a computer implemented algorithm. During the first half of a trial, the contrast increases quickly to a point just below an expected threshold, and in the second stage the contrast increases slowly until a threshold is reached. Details and advantages of the algorithm are presented as well as a comparison of data generated by this and other techniques.

Multi-flash campimetry in multiple sclerosis.

Data are reported from the initial stage of development of a psychophysical technique that allows temporal resolution to be sampled in 120 retinal locations per eye in half an hour. This computer generated test consists of systematically increasing the off period of a small spot of light, temporally modulated at 5 Hz, until the light is perceived as flickering. Visual field plots based on the data from control observers reveal good temporal resolution in the central visual field with a fall-off in resolving power in peripheral regions. Data from multiple sclerosis patients are characterized by "islands" of poor temporal resolution that presumably reflect demyelination along the optic nerve.

Backward pattern masking can vary as a nonmonotonic function of target duration: on the influence of intratraget metacontrast.

The magnitude of backward masking is usually found to vary inversely with the amount of information about a target that is made available to the visual system. Contrary to these findings, we report a nonmonotonic relation between the magnitude of backward pattern masking and target duration. Specifically, masking decreased as target duration was increased to about 8 msec and, then, became more severe as target duration was further increased to a value of at least 40 msec. The occurrence of the nonmonotonic function depended on (a) the degree of definition of the target's edges, (b) the luminance levels within the target stimulus, and (c) the state of adaptation of the eye. It is hypothesized that the source of the nonmonotonic function was metacontrast interference that originated from within the target stimulus configuration. This hypothesis was supported by data that indicated that in the absence of any mask presentations, the apparent contrast between the target and its immediate background varied as a nonmonotonic function of target duration.

Sensory information and subjective contour.

The possibility that subjective contours are an artifact of brightness contrast was explored. In one experiment, inducing luminance was found to have different effects on the clarity of subjective contours and the magnitude of brightness contrast. The results of a second experiment indicated that differences of luminance in a stimulus display are necessary for subjective contours to be sustained, whereas chromatic differences are not. It is concluded that subjective contour and brightness contrast are distinct perceptual phenomena but share a dependency on the processing of edge information transmitted through the achromatic channels of the visual system.

The aftereffect of tracking eye movements.

When observers tracked moving stripes across a background either of stationary stripes, or of stripes moving in the opposite direction, they saw a clear motion aftereffect when the stripes stopped moving. The direction of this aftereffect was opposite to that of the previously tracked stripes, and was thus the same as the direction of the retinal movement of the non-tracked stripes. This aftereffect of tracking was shown not to depend upon slippage of the tracked contours on the retina during tracking, or upon the saccadic phase of optokinetic nystagmus. The effect showed storage over a period of time with the eyes shut. It appears that the effect is due to induced movement, and arises originally from stimulation of the retina by background contours in the tracking phase. This was shown by confining the view of the moving target to one eye, while permitting both eyes to be exposed to background stimulation during tracking. After such stimulation the magnitude of the aftereffect was equal in the two eyes.