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To compare the modified signal-to-noise ratio (SNR*) of multifocal visual evoked potential (mfVEP) responses elicited by a cathode ray tube (CRT) and liquid crystal display (LCD) monitor in normal subjects. An LCD monitor and CRT monitor were luminance and contrast matched. Luminance stability and the effect of viewing angle on luminance and contrast was measured for both screens. The SNR* of mfVEP responses from 15 normal subjects was compared between the stimulators using repeated measures analysis of variance. The CRT monitor took 10 min from switch on to reach the desired luminance compared to 60 min for the LCD monitor. LCD luminance was sensitive to variations in ambient temperature, fluctuating by 10 cd/m−2 over approximately 20–27 °C, whereas CRT luminance was stable. Luminance variation from the centre to the edge of the CRT screen was 8 % when viewed perpendicularly and 28 % when viewed at an angle of 25°, compared to 24 and 46 %, respectively, for the LCD screen. Contrast was >94 % and varied by

The mfERG provides a topographic map of function of the retina and has been used in numerous studies to identify macular, paramacular and peripheral retinal dysfunction. This study investigates the changes in response due to the presentation rate of the stimulus. Twenty subjects gave informed consent to take part in the study, which had local regional ethical committee approval. Only a single hexagon of 8° diameter was presented to reduce ambiguity when identifying the higher-order kernels (HOK). Six rates were tested using a 60-Hz CRT monitor by introducing blank (black ~0 cd/m2) filler frames (FF). The rates tested were 0FF; 1FF; 2FF; 4FF; 7FF; and 14FF. The first-order kernel had largest responses to the slower stimuli (4FF and above). HOK had largest amplitudes at faster rates with the second-order kernel peaking at 1FF. At rates with 4FF and slower, the higher-order kernels were indiscernible above the noise.

The mfERG has proven to be a useful tool in determining central retinal and macular function. It is, however, reliant on good subject co-operation and fixation. This cannot always be guaranteed due to visual impairment or poor co-operation. Whilst a change in fixation is easy to identify with camera monitoring of the subject, a small eccentric fixation can be difficult to notice or quantify. Whilst the problem of fixation can be obviated by stimulating the retina directly with SLO (Scanning Laser Ophthalmoscope), this is expensive and a certain amount of expertize in optics is required to properly stimulate the retina. In this study, peak latency of response was investigated to see whether it changed across the retina and whether this measure could be used to help assess fixation. Eighteen normal eyes were stimulated using a 60 Hz CRT monitor with only 2 hexagons, one central and one peripheral. These hexagons were presented at three stimulation rates, fast (no filler frames between steps of the m-sequence) and slow (4 and 7 black filler frames between each step of the m-sequence), under all conditions significantly increased central hexagon latencies were noted. In a smaller experiment with 19 hexagons and only 4 subjects, it was noted a significant delay in latency was observed in ring 1 compared to ring 2 and 3 with central fixation, but not when the subjects fixed mid-peripheral and in the periphery to slow stimulation, showing that the central hexagon response was only delayed in the central hexagon when there was adequate fixation. This study suggests that latency could provide a clue to fixation particular at slow rates thereby improving the quality and confidence of recordings made clinically.